Masters Degrees (Animal Sciences)

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Carcass traits in relation to genotype in sheep
(Stellenbosch : Stellenbosch University, 2002-04) Cloete, Jasper Johannes Erasmus; Hoffman, Louwrens C.; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
ENGLISH ABSTRACT: Experiment 1: Two studies were conducted to research the effect of divergent selection for multiple rearing ability on carcass weight, mutton production, meat quality and carcass characteristics of similar-aged Merino sheep. Data of 114 19-month-old Merino sheep, 40 ewes and 74 rams were used in this study. The study was done in two parts over 2 years. Only rams (52) were slaughtered over a two-week period in study A. Twenty-two rams and 40 ewes were slaughtered over a three-week period in study B. The sheep were descended from two selection lines that have been divergently selected for maternal multiple rearing ability since 1986. In brief, ewe and ram progeny of ewes rearing more than one lamb per joining (i.e. that reared twins at least once) were preferred as replacements in the high (H) line. Descendants of ewes that reared fewer than one lamb per joining (i.e. that were barren or lost all lambs born at least once) were preferred as replacements in the low (L) line. In study A the mean (±SE) slaughter weight of H line rams . were 12% heavier (P0.05). The difference between the weight of the loin retail cut remained significant (P0.05). Hindquarter weight still remained significantly (P
A comparison of Merino and Dormer rams in terms of mating dexterity and sperm subpopulations characteristics
(Stellenbosch : Stellenbosch University, 2016-12) Langeveldt, Juanita; Lambrechts, Helet; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Assisted reproductive techniques (ART’s) play an increasingly important role in sheep farming systems to ensure the viability and cost-efficiency of production. Sperm quality is a major determinant of the successful application of ART’s, and therefore it is important to understand the factors that affect the viability and fertilizing ability of sperm. This study aimed to determine the influence of breed and genetic selection for reproduction potential on mating dexterity, sperm morphometric subpopulation characteristics and fertilizing ability. The technique used to collect semen samples can influence the quality of the sample, with the artificial vagina (AV) method yielding better samples than those collected by means of electro-ejaculation (EE). The use of the AV method requires the prior training of rams, and to date no standard operational procedure (SOP) has been formulated for the training of rams to use the AV. During the training of rams to use the AV, both inexperienced and experienced Dormer rams found mature Dormer ewes more attractive than yearling Dormers ewes, and in the training sessions the Dormer rams did not discriminate between Dormer and Merino ewes (in oestrus), that were used as teaser ewes to stimulate a sexual response in the rams. In contrast, Merino rams in this study were less discriminatory in their choice for either mature or yearling Merino ewes, with experienced Merino rams exhibiting a definite preference for a Merino teaser ewe. There was no conclusive evidence of a breed preference in inexperienced Merino rams. Breed and degree of sexual experience did not influence ease of habituation of a ram to the presence of the semen collector and/or assisting staff. Rams could be habituated within approximately 4 weeks and during a minimum of 8 training sessions when trained by experienced personnel. A higher frequency of training, i.e. 18 training sessions during this 4-week period will result in a more established baseline behaviour that will indicate whether a ram could be successfully trained to use the AV. There was no conclusive evidence that experienced Merino or Dormer rams ejaculated into the AV more readily, when compared to the Dormer and Merino inexperienced rams. It has to be noted that only 50% of the experienced Dormer rams could be successfully trained to use the AV, compared to 90% of the experienced Merino rams. Of the inexperienced rams only 40% of both the Merino and Dormer breeds could be trained to use the AV. Four distinct sperm morphometric subpopulations were identified in semen samples obtained from Dormer and Merino [High reproduction potential line (HL) and Low reproduction potential line (LL)] rams in this study. No significant differences were reported between the breeds in terms of ejaculate sperm subpopulation structure. The sperm subpopulation analysis of the HL and LL ejaculates indicated minor but non-significant differences between certain subpopulations. Breed or genetic selection had no influence on most post-thaw sperm parameters, except for post-thaw sperm viability that differed between HL and LL rams. A significant difference was observed between the sperm binding capacity of Dormer and Merino sperm. Sperm obtained from HL rams tended to have a better binding capacity than sperm obtained from the LL rams. No conclusive evidence of a correlation between sperm binding capacity and any sperm morphometric subpopulation was obtained. In conclusion, the factors contributing to the difficulty of training experienced Dormer rams, as well as inexperienced Dormer and Merino rams, to use the AV warrants further investigation. Future studies should further investigate the influence of breed and genetic selection on sperm subpopulation traits. Additional research to clarify the relationship between sperm subpopulations traits and the potential role of sperm competition in the determining the fertilizing potential of sperm, is warranted.
Development of a model for crossbred lamb production
(Stellenbosch : Stellenbosch University, 2021-12) Theron, Pietert Gert; Brand, T. S.; Cloete, Schalk W. P.; Van Zyl, Johan Hendrik Combrink ; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Historically the sheep industry has played an important role in the South African agricultural landscape, but due to changing circumstances and growing challenges it may find its continued survival under threat. Producers will therefore need to find ways of improving production output and efficiency to meet these challenges. This study therefore aimed to collect production data of crossbred sheep in order to construct predictive models that could be used as part of a precision livestock farming (PLF) system by producers. Two common wool producing breeds, the Dohne Merino and Merino, were selected as dam lines for this experiment. A mixed flock of these ewes were divided into breed specific groups of 20 and each group then mated to rams of their own breeds or with Dorper, Dormer or Ile de France rams as the most important meat and terminal sire breeds. This resulted in two purebred control lines (Dohne Merino and Merino) and six crossbred trial lines (Dohne x Dorper, Dohne x Dormer, Dohne x Ile de France, Merino x Dorper, Merino x Dormer and Merino x Ile de France) being produced. Four rams and four ewes of each genotype were reared under optimal growth conditions until one year of age. During this time growth, fat deposition and intake data were collected. The data thus generated were assessed with various regression models to predict growth and fat deposition as well as feed intake. The Gompertz growth model provided the best fit for the growth data while a linear regression of age on fat depth was the most accurate in predicting fat deposition rate. An accurate model for cumulative feed intake over the growth period was also constructed. At the end of this period the lambs were shorn and wool traits of economic importance assessed. The remaining lambs were weaned at ~31 kg and reared on pastures with no supplementary feed being provided until they were deemed slaughter ready at 4 mm of backfat depth (A2 carcass classification). The growth of these lambs was also monitored and subsequently modelled, where the Logistic model provided the best fit. Upon achieving slaughter readiness, the lambs were slaughtered and selected slaughter and carcass traits recorded. Overall it was found that rams outperformed ewes for the production traits studied. This is due to sexual dimorphism benefiting rams for these traits. Crossbred lambs also had a significant advantage over their purebred contemporaries for all the traits except feed efficiency and wool quality. This was attributable to a combination of heterosis for these traits as well as breed dimorphism between the smaller dam and larger sire lines. The increased degree of breed dimorphism between Merinos and the sire breeds meant that the improvement in the performance of crossbred Merino lambs relative to the dam line was greater than the corresponding performance improvement in Dohne Merinos. It is concluded that crossbreeding offers a viable method of improving commercial production efficiency in South African Dohne Merino and Merino flocks. Producers who wish to implement a PLF system for a terminal crossbreeding enterprise can now do so using guidelines from this study. It is advised that further work be done on various crossbreeding options to expand the current local knowledge. More crosses could be included in future research while more complete models for pasture-rearing systems would also be of benefit to the industry.
The effect of agricultural production system on the meat quality of Dorper lambs
(Stellenbosch : Stellenbosch University, 2008-03) Claasen, Claasen; Hoffman, Louwrens C.; Cloete, Schalk W. P.; Cloete, J. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The aim of this study was to investigate the effect of South African production system (feedlot {FL-} or free-range {FR-}) and gender (ewes, rams or castrates) on growth and carcass characteristics of Dorper sheep. Male lambs (castrates and rams) grew twice as fast as ewes (P<0.05) under FL-conditions while much smaller differences were observed between gender groups in FR-lambs. FL-lambs produced heavier carcasses (P=0.0003) with higher dressing percentages (P<0.05) and greater carcass fatness levels (P<0.052) than FR- lambs. No differences attributable to production system were found on meat tenderness (as indicated by Warner Bratzler shear force strength) and on the intramuscular lipid concentration. In contrast, sensory evaluation results suggested that meat from FL-lambs was juicier and more tender than meat from FR-lambs. The sensory panel could not distinguish between FL and FR meat as far as the attributes of aroma and flavour were concerned. Cholesterol results indicated that for intermuscular fat, higher cholesterol levels were observed for FL-lambs than for FR-lambs. The level of palmitic acid (C16:0) was significantly higher (P=0.0375) in the Longissimus dorsi (LD) muscles of FL-lambs. For intramuscular fat from the Biceps femoris (BF) muscle, g-linolenic acid (C18:3n-6) was higher (P<0.0001) in FL- lambs. Results for intramuscular BF further indicated that ram lambs had the highest (P=0.0019) palmitic acid (C16:0) and sum of TUFA (P=0.0014), castrates had the highest (P=0.0260) α-linolenic acid (C18:3n-3) and g-linolenic acid (C18:3n-6), while ewe lambs had the highest (P=0.0014) SFA concentrations. Linoleic acid (C18:2n-6c) was significantly higher (P=0.0067) in the subcutaneous fat of FL-lambs while FR-lambs had more linolenic acid (C18:3n-3). For the kidney fat, FR-feeding increased (P < 0.05) stearic (C18:0), linolelaidic (C18:2n-6t), α-linolenic (C18:3n-3) and homo-g-linolenic acid (C20:3n-6) percentages. Conversely, linoleic acid (C18:2n-6c) was increased (P=0.0372) by FL-feeding. For the intermuscular fat, FR-lambs had higher linolenic acid (C18:3n-3) and SFA (P=0.0113 and P=0.0341) compared to FL-lambs. On the other hand, the sum of TUFA for the intermuscular fat was higher (P=0.0341) in FL-lambs compared to FR-lambs. Results from the study imply that the consumer may not necessarily be able to discern between meat from FR- or FL-lambs, although they may possibly discriminate against the increase in visible fatness of FL-lambs. No clear advantage of production system in terms of human health could be demonstrated as far as the proximate chemical composition and the fatty acid composition of the meat was concerned. The faster growth and the associated shorter production cycle of FL-lambs could be an advantage under certain production systems. However, it needs to be weighed against the cost of concentrate feeding and the preference consumers are likely to develop for lamb produced in natural environments.
Enhancing the breed analysis of the Dohne Merino by accounting for heterogeneous variances and phantom parents
(Stellenbosch : Stellenbosch University, 2013-12) Jordaan, Wilmari; Cloete, Schalk W. P.; Dzama, Kennedy; Olivier, J. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Genetic (co)variances for body weight, clean fleece weight and fibre diameter were estimated for the South African Dohne Merino using data transformed as proportions of contemporary group means. The data analysed included body weight, clean fleece weight and fibre diameter records for 282 513 animals, evaluated between 1992 and 2011. There were 5 698 sires, 105 886 dams and 6 291 contemporary groups in the data. A three-trait animal model was fitted, where the random variables were the direct additive genetic effects, as well as the sire-flock-season (SFS) interaction, while the fixed effects included contemporary groups (FYSSM) (6 291 classes), birth status (single, twins or triplets), age of dam (1 to 3 years), which was plotted as a linear regression as well as age at performance measurement, which was fitted as a polynomial. The direct heritability estimates (SE) for body weight, clean fleece weight and fibre diameter were 0.265 (0.005), 0.210 (0.004) and 0.437 (0.005), respectively. Genetic correlations for body weight with clean fleece weight and fibre diameter were 0.035 (0.015) and 0.139 (0.011), respectively, while the genetic correlation between clean fleece weight and fibre diameter was 0.169 (0.012). Body weight had phenotypic correlations of 0.327 (0.002) and 0.150 (0.002), respectively, with clean fleece weight and fibre diameter, which had a phenotypic correlation of 0.190 (0.002) with clean fleece weight. The moderate to high heritability estimates suggests that there is substantial genetic variation, which may result in genetic improvement if selection is applied on these traits. Genetic correlations were generally low, suggesting that progress in all these traits was possible in a scientific selection program. Genetic trends derived during the study supported the contention that genetic progress in all traits was attainable in a well-constructed breeding programme. Transformation of the data to percentages of contemporary groups resulted in adjustments to breeding values. The breeding values for sires originating from flocks maintained in limiting environments (Low group; 180 sires) were adjusted upwards, while those of sires originating from a non-limiting production environment (High group; 146 sires) were adjusted downwards. These effects were markedly obvious for the quantitative traits (body weight and clean fleece weight), but to a much lesser extent for fibre diameter. This transformation resulted in the genetic trends for the Low groups being adjusted to be comparable to those in the High group for body weight and Fibre diameter. It was concluded that sire breeding values derived from transformed data would be more robust across the typical diverse environments supporting local Dohne Merino production. The genetic value of animals entering the recorded population from a commercial base (F4 animals) was below the fully recorded part of the population. The inclusion of phantom parent groups in the genetic analysis rendered genetic trends in F4 animals comparable to that of the pedigreed portion of animals in the analyses. It was concluded that animals from a commercial base (which are alleged to have advantages in terms of fitness and robustness) were more likely to perform satisfactorily for selection with the inclusion of phantom groups than without it. It was recommended that data in the national Dohne Merino analysis be transformed proportion of contemporary group means to account for heterogeneous contemporary group variances. Phantom parent groups should also be applied to the analysis to increase the probability of those animals entering the breeding flock from a commercial base being selected.
Estimation of genetic distances and heterosis in three ostrich (Struthio camelus) breeds for the improvement of productivity
(Stellenbosch : University of Stellenbosch, 2011-03) Davids, Annelin Henriehetta; Cloete, Schalk W. P.; Dzama, Kennedy; University of Stellenbosch. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: A study was conducted to characterize the three ostrich breeds available as genetic resource in South Africa, namely the South African Black (SAB), Zimbabwean Blue (ZB) and the Kenyan Redneck (KR), and their respective crosses. Growth, slaughter traits and reproduction of these ostriches were recorded at Oudtshoorn Research Farm in the Western Cape of South Africa. Individual non-linear regressions (Gompertz) were fitted to the data of 390 purebred and 41 crossbred ostriches, using the SAS NLIN function. Heterosis was estimated for each parameter of the Gompertz model. The estimated adult weight (Aparameter) of the ZB (147 kg) and the KR breeds (148 kg) were higher than that of the SAB breed (129 kg). The overall growth rate (B-parameter) of the ZB breed (0.0075) and the SAB breed (0.0080) was lower than that of the KR (0.0150). The age at maximum weight gain (C-parameter) was higher for the ZB breed (226 days) compared to the SAB (198 days) and the KR (194 days). Heterosis for the A-parameter was estimated at -6.2% and at -12% for the C-parameter. The slaughter traits studied were slaughter weight (SLW), carcass weight (CW), dressing percentage (DP), fan fillet weight (FFW), pH0, pH24, drip loss % (DL%), cooking loss % (CL%), tenderness and meat colour traits. Differences were observed between the means for SLW of the SAB (86.5 kg) and ZB (93.9 kg). Mean DP of the KR breed (52.5%) was increased relative to the low DP of their SAB contemporaries (48.8%). The sire lines (ZB and KR) and crosses were heavier than the SAB (dam line), whereas the crosses resembled the dam line for meat quality traits. Means for pH24 also differed, with higher values for the sire lines (ZB – 6.36; KR – 6.4) relative to the SAB (5.85). The instrumental b* colour value also differed between the SAB (9.4) and KR (6.9). Records used for assessing the reproduction and body measurements of purebred and crossbred dams were 428 in total. Traits analyzed were, total egg production (TEP), the number of fertile eggs, number dead in shell chicks, hatchability and chick production (CP), the time to lay, live weight, front chest circumferences as well as tail circumference. The ZB and KR were heavier in live weight and of larger body measurements than the SAB, whereas the SAB exhibited superior reproduction performance in comparison with the ZB and KR breeds. Derived heterosis estimates amounted to 2.2% for tail circumference, 12% for TEP, 12% for hatchability and 19% for CP. Genetic variation between and within the breeds were determined utilizing 19 microsatellite markers. Significant molecular genetic differences were observed between the three breeds. The SAB and ZB (Fst = 0.10 and Nei = 0.49) were genetically most similar, whereas the genetic distance between the KR and ZB breeds were furthest (Fst = 0.13 and Nei = 0.61). The SAB breed exhibited the highest heterozygosity within its population and the ZB the lowest heterozygosity. These results contribute to a better understanding of the utilization of the distinct ostrich breeds for commercial production.
Genetic analyses of South African terminal sire sheep breeds
(Stellenbosch : University of Stellenbosch, 2009-03) Zishiri, Oliver Tendayi; Cloete, Schalk W. P.; Dzama, Kennedy; Olivier, J. J.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Fluctuations and a general decline in the ratio between wool and meat prices resulted in marked changes in the South African sheep industry. Commercial producers now exploit other mechanisms such as terminal crossbreeding of Merino-type with meat type breeds or dual-purpose breeds to attain short-term benefits resulting from price fluctuations between wool and mutton without compromising the wool-producing capacities of ewe flocks. Most components of lamb production have low heritability. However, heterosis can be achieved by mating wool-type breeds with specialist meat breed rams. Genetic improvement of livestock depends on defining breeding objectives, estimation of genetic parameters and accurately identifying the right animals to be used for future breeding. Genetic parameters for traits of economic importance in terminal sire sheep breeds that could be used on Merino-type ewes in commercial operations in South Africa had not been published for the national flock apart from a preliminary study having been conducted by Olivier et al. (2004). Selection objectives were poorly defined due to lack of parameter estimates for variance and covariance components. Against this background, this study obtained pedigree information and live weight data from the National Small Stock Improvement Scheme for the Dormer, Ile de France and Merino Landsheep and estimated non-genetic factors and genetic parameters influencing early growth traits. Genetic and phenotypic trends for early growth traits were constructed for the three breeds to monitor genetic progress. Non-genetic factors influencing early growth traits in the Dormer, Ile de France and Merino Landsheep were estimated using data obtained from the National Small Stock Improvement Scheme of South Africa. The original data sets for the Dormer, Ile de France and Merino Landsheep consisted of the following number of records respectively: 52 202, 35 553 and 7 772. However, pre-weaning weights were available for the Ile de France and Merino Landsheep breeds only and post-weaning weights were available only for the Dormer breed. The data sets were complicated to such an extent that smaller data sets had to be generated to analyse for fixed effects. The traits that were analysed were birth weight, pre-weaning weight, weaning weight and post-weaning weight. The fixed effects, identified as having a significant effect (P < 0.01) on early growth traits were sex of lamb, birth type, age of dam, contemporary groups, age at which the trait was recorded and month of birth and year of birth in the Merino Landsheep breed. Although some significant interactions were found, they were subsequently ignored owing to their very small effects. In all three breeds, male lambs were significantly (P < 0.001) heavier than female lambs and single-borne lambs were significantly heavier at birth than multiple borne lambs. The age of dam had a significant curvilinear regression on all early growth traits in all three terminal sire sheep breeds. It was concluded from the study that the influence of non-genetic factors on early growth traits should be adjusted for or eliminated statistically in genetic evaluations to get accurate genetic parameter estimations. (Co)variance estimates for birth weight, weaning weight and post-weaning weight were obtained for the Dormer breed using restricted maximum likelihood procedures (REML). Direct heritabilities (h2) in single-trait analyses were 0.21 ± 0.03, 0.23 ± 0.02 and 0.29 ± 0.05 for birth weight, weaning weight and post-weaning weight, respectively. Direct heritabilities of 0.28 ± 0.04, 0.55 ± 0.06 and 0.32 ± 0.02 for birth weight, weaning weight and post-weaning weight respectively were obtained using three-trait analysis. Direct maternal genetic effects (m2) were excluded from the analyses because of the failure to partition maternal effects into maternal genetic and maternal permanent environmental effects (m2 and c2). This culminated as a consequence of poor data and population structures emanating from the loss of genetic links across flocks due to the random entrance and exit of flocks from the recording scheme. Maternal permanent environment was estimated at 0.15 ± 0.02, 0.13 ± 0.02 and 0.20 ± 0.03 for birth weight, weaning weight and post-weaning weight respectively using single-trait analysis. The correlation between direct effects and maternal effects (ram) was excluded from the analyses due the structure of the data. Genetic, phenotypic and environmental correlations between early growth traits were low to moderate. The medium to high heritability estimates for early growth traits obtained in the study led to the conclusion that Dormer sheep can successfully be used in terminal crossbreeding programs to improve meat production characteristics. Direct heritability estimates were 0.31 ± 0.14, 0.09 ± 0.02 and 0.14 ± 0.003 for birth weight, pre-weaning weight and weaning weight respectively using single-trait analysis for the Ile de France breed. Maternal effects were significant for all the traits studied despite the failure to properly partition them into their components due to the loss of genetic linkages across generations emanating from poor data structure. Genetic, phenotypic and environmental correlations were estimated using three-trait analysis and were found to be low to moderate for early growth traits. Direct genetic and maternal permanent environmental ratios were also computed and they did not differ much from the results obtained using single-trait analyses. The reasonable genetic parameter estimates obtained in the study led to the conclusion that the Ile de France can be selected to use as sires in crossbreeding programs. Genetic parameters were estimated for early growth traits in the Merino Landsheep breed. REML estimates of birth weight, pre-weaning weight and weaning weight were obtained using animal models in single-trait analyses. The direct heritability estimate for birth weight was 0.23 ± 0.13 using an animal model with additive direct genetic effects and dam permanent environmental effects as the only random factors. The dam permanent environmental effect for birth weight amounted to 0.10 ± 0.07. Direct heritability for pre-weaning weight was 0.36 ± 0.05 and the dam permanent environmental effect 0.56 ± 0.03. Weaning weight was estimated using an animal model that contained direct additive effects and dam permanent environmental effects. The direct heritability estimate for weaning weight was 0.17 ± 0.03. Maternal genetic effects were estimated to be 0.02 ± 0.01. Genetic and phenotypic trends were constructed for early growth traits in the Dormer, Ile de France and Merino Landsheep breeds. The traits that were considered were birth weight, pre-weaning weight, weaning weight and post-weaning weight. However, pre-weaning weights were available for the Ile de France and Merino Landsheep breeds only and post-weaning weights were available only for the Dormer breed. The Dormer exhibited significant improvement in the phenotypic and genetic aspects of early growth traits during the 17 years of evaluation (1990-2007). The average predicted direct breeding values of birth weight decreased by 0.055 % during the evaluation period. The predicted direct breeding value for weaning weight increased by 0.12 % during the 17 year period. Post-weaning weight improved by 0.32 % per annum. The Ile de France registered an increase in the predicted breeding value of birth weight which amounted to 0.025 % per annum. Averaged direct breeding values for pre-weaning weight increased at an annual rate of 0.23 %. and that of weaning weight increased by 1.21 %. In the Merino Landsheep the predicted direct breeding value for birth weights decreased by 0.04 % per annum and pre-weaning and weaning weights increased by 0.36 % and 0.10 % respectively. The trends were obviously biased due to inconsistencies in data structure and very few records available for analysis in this breed. In conclusion, it was evident that the additive genetic variation was available for all the early growth traits in all the three breeds. Although adequate genetic variation for substantial genetic progress was available, only modest rates of progress were attained for all the traits in all three breeds. The only possible exception was weaning weight in the Ile de France breed, which improved at > 1 % per annum. At least all changes were in the desired direction. Breeders should be encouraged to record data consistently, as one of the major shortcomings in the data for all breeds were a lack of continuity in the submission of data to the NSIS. More informative analyses ought to be feasible if this requisite could be met.
A genetic study of early growth traits and ewe productivity in merino sheep
(Stellenbosch : Stellenbosch University, 2001-12) Jaleta, Gemeda Duguma; Schoeman, S. J.; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The objectives of this study were to investigate genetic parameters of early growth traits, lifetime ewe productivity (total number born, number weaned and weight weaned per ewe lifetime production) and testis measurements in the Merino flock maintained at the Tygerhoek Experimental Farm. Non-genetic fixed factors influencing these traits were evaluated by using appropriate models. The influence of non-genetic factors on preweaning lamb survival rate and the effect of scrotal circumference on ewe fertility was also studied. Fixed effect models were fitted to the data using either Procedure GLM or CATMOD in SAS (1996) depending on the parameters being estimated. Variance components were estimated by Restricted Maximum Likelihood (REML) procedures, fitting an animal model. Records of 8310 lambs born from 2538 ewes and sired by 681 rams covering the period 1970 to 1998 were used in the analysis of birth weight (BW), weaning weight (WW) and preweaning average daily gain (ADG). All three traits were affected (p < 0.001) by type of birth of lambs (single, multiple), sex, year of birth of lambs, group of animals (selection, control) and age of dam at lambing (2- to 6-yr old). Male lambs and singles were heavier both at birth and weaning and grew faster (p < 0.001) than females and multiples, respectively. Non-selected animals were lighter than selected animals at birth and weaning with an inferior growth rate. BW increased with increasing dam age at lambing until a maximum of 3.7 kg was reached at 6-yr of age. However, WW and ADG reached a maximum at 4.5- and 4.2-yr of age, respectively. Variance components for BW, WW and ADG were estimated using Restricted Maximum Likelihood (REML) procedures. Four different animal models were fitted, differentiated by including or excluding maternal effects. The direct heritability estimates (h") ranged from 0.19 to 0.38, 0.25 to 0.40 and 0.26 to 0.40 for BW, WW and ADG, respectively. Estimates of direct heritability (h") were substantially higher when maternal effects were ignored. The direct heritability (h") estimate for BW decreased from 0.38 to 0.19 when both or either of the maternal effects, genetic or environmental, were fitted in the model. The h2 estimate for WW was 0.36 when both maternal effects were ignored from the model and decreased to 0.29 and 0.25 when maternal effects were fitted. A similar trend was observed for ADG. The maternal heritability (rn-) for BW ranged from 0.38 to 0.41 when only maternal additive genetic effects were fitted in the model, and decreased to 0.25 and 0.27 when the maternal permanent environmental effect (c") was fitted. The m" for WW and ADG ranged from 0.02 to 0.11 and from 0.01 to 0.10, respectively. The respective c2 estimates ranged from 0.05 to 0.10 and from 0.02 to 0.09. Moderate negative genetic correlations (ram) between direct and maternal additive genetic effects were observed in BW, while close to zero estimates were obtained for WW and ADG. The direct additive genetic correlation estimates between BW and WW and BW and ADG were 0.16 and 0.04, respectively. The corresponding maternal additive genetic correlation estimates were 0.93 and 0.60. The direct and maternal additive genetic correlation estimates between WW and ADG were 0.99 and 0.85, respectively. Data of 3272 lambing records collected on 818 ewes born from 689 dams and sired by 371 rams were used in the evaluation of ewe lifetime productivity (total number born, number weaned and total weight weaned). These records were collected from ewes born from 1969 to 1994 and gave birth from 1971 to 1999. Year of birth of ewe and ewe two-tooth liveweight affected (p < 0.001) the ewe reproduction traits investigated. Multiple born ewes were superior both in total number of lambs born and weaned than singles. Heritability estimates of 0.23, 0.17 and 0.20 were obtained for total number of lambs born (TLB), total number of lambs weaned (TLW) and total weight of lambs weaned per ewe lambing over four lambing opportunities (TWW), respectively. For total weight weaned per ewe lambing over the first lambing opportunity (TWWl) a heritability estimate of 0.02 was computed. Genetic correlation estimates of -0.10, 0.57 and 1.00 were obtained between TWW1 and TLB, TWW1 and TLW and TWWl and TWW, respectively. High and positive genetic correlations ranging from 0.61 to 0.92 were estimated between ewe lifetime reproduction traits. Data from 1380 rams born from 1986 to 1998 were used to investigate genetic parameters for scrotal circumference (SC), testis diameter (TD) and two-tooth liveweight (LW). The other objective of this study was to estimate the magnitude of the effect of SC on ewe fertility. Year of birth, selection group and LW were significant (p < 0.001) sources of variation both for SC and TD. Heritability estimates ranged from 0.29 to 0.40, 0.25 to 0.38 and 0.49 to 0.52 for SC, TD and LW, respectively. Adjustment for LW decreased heritability estimates of SC and TD by 11.0 and 8.0 %, respectively. The genetic correlation between SC and TD was unity. Rams with larger SC had a significant effect on ewe fertility (ewes lambing per ewe mated). Average survival rate from birth to 100 days of age was 0.79 and was influenced by lamb birth weight, year of birth, age of dam at lambing, type of birth (single, multiple) and sex of lambs. Lambs with a liveweight between 4.0 to 4.9 kg at birth showed the highest survival rate while lambs with a liveweight of:s 2.0 kg showed the lowest survival rate.
Improving ostrich welfare by developing positive human-animal interactions
(Stellenbosch : Stellenbosch University, 2018-03) Muvhali, Pfunzo Tonny; Bonato, Maud; Cloete, Schalk W. P.; Malecki, I. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences
ENGLISH ABSTRACT: Animal welfare has recently gained significant attention in commercial livestock industries worldwide. Specifically, several studies involving husbandry practices with positive human-animal interactions have shown a favourable link between improved animal welfare and production. However, limited research is currently available on optimal husbandry practices for the ostrich industry, which is still plagued by low fertility, high embryo and chick mortality, as well as variable growth rates. The poor ostrich production performance observed could thus reflect the difficulties of the birds to adapt to the commercial farming systems, and/or a failure of commercial practices to provide the basic requirements for this newly domesticated species. Hence, this study examined the effect of different husbandry practices varying in the intensity of human presence and interactions with ostrich chicks from day-old to 3 months of age on: weight gain, survival, immune competence, short- and long-term stress responses, social behaviour, docility, fear responses, meat quality and skin damage. The reproduction performance when the birds reached sexual maturity also was recorded. The study showed that exposure to additional human contact (as compared to standard husbandry practices where human contact was limited to the provision of food and water), resulted in improved early growth, survival and immune competence, and even more so when chicks were exposed to gentle physical handling interactions. Furthermore, chicks exposed to such human presence and interactions expressed lower short-term stress responses when exposed to a potentially stressful event (i.e. feather harvesting and feather clipping), and lower long-term stress responses (as measured in corticosterone levels in the floss feathers), compared to chicks exposed to limited human presence. These results suggest an improved ability of the former to adapt to routine ostrich farm management practices. Furthermore, while social behaviour, docility and fear responses to humans when the birds reached the juvenile stage did not vary between the different husbandry practices, the birds habituated to human presence at an early age were more likely to associate with a familiar rather than an unfamiliar human. This suggests that ostriches can not only discriminate between people, but also adjust their behaviour accordingly. Husbandry practices did not affect meat pH, meat colour, carcass attributes or skin damage. Females that received additional human presence along with physical gentle handling produced a higher number of eggs in their first year of reproduction as 2-year-olds, compared to females that were exposed to limited human presence. The difference in egg production was not observed during the second year of breeding. Hence, additional human presence combined with gentle physical handling seemed to improve early egg production and adaptation of females to the breeding environment. The results of this study revealed that positive human-chick interactions could potentially alleviate problems associated with ostrich chick rearing, by reducing stress sensitivity while improving production performance. More specifically, this study has highlighted promising ways to overcome major constraints faced by ostrich farmers. A slight change of current management practices, through increasing positive human-animal interactions with these relatively wild animals has shown to be beneficial. However, further studies are required to assess the financial viability of these alternative husbandry systems. This will entail promoting animal welfare by comparing economic costs associated with different levels of animal welfare and the associated production performance in these production systems.
The influence of genotype on sperm motility and sperm head morphometry of Merino (Ovis aries) sheep
(Stellenbosch : Stellenbosch University, 2014-04) Boshoff, Ninja Hettie; Lambrechts, Helet; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The application of assisted reproductive biotechnologies in sheep flocks is hampered by the susceptability of ovine sperm to cryodamage. There is still considerable scope in the improvement of cryopreservation protocols for ovine sperm to minimize the degree of damage to sperm during the cryopreservation process. Pre-cryopreservation processing has a definite effect on the survivability, motility, and fertilizing ability of sperm. Little information is however available on the potential contribution of the genetic make-up of rams, divergently selected for fecundity, on the ability of sperm to offer resistance to the damage caused by cooling, cryopreservation and thawing. The study aimed to investigate the influence of genetic selection for prolificacy (i.e. High Merino Line and Low Merino Line in terms of fecundity) on the ability of ovine sperm to offer resistance to cryodamage. The study investigated the effect of pre-cryopreservation processing by comparing motility and morphometry traits recorded for fresh- and post-thaw Merino ejaculated and epididymal sperm samples obtained form the High and Low lines, respectively. The effect of different sperm concentrations, equilibration periods and the addition or omission of seminal plasma from cryopreserved samples on the viability and morphometrical traits were also investigated. Ejaculate samples were collected by means of the artificial vagina (AV) method from 8 High Line rams and 7 Low Line rams. Epididymal samples were collected from 6 rams of each of the High and Low lines respectively, by recovering the epididymal sperm via aspiration from the cauda epididymides post mortem. Ejaculate samples were subjected to macroscopic and microscopic evaluation, and epididymal samples only to microscopic evaluation, for which the Sperm Class Analyzer® program was used for the evaluation of motility and morphometric measurements. Sperm motility recordings were captured at 100 frames per second. From findings of the study, it was concluded that genotype had no positive influence on the conception rate of the ewes mated to the High or Low Line rams, even though the rams from the two lines differed significantly in terms of their serving capacity. When sperm morphometry was evaluated for fresh ejaculate samples, the two lines differed significantly in terms of the morphometric traits elongation and ellipticity. Epididymal and ejaculated sperm obtained from Low Line rams had broader and rounder heads, compared to sperm obtained from High Line rams. When morphometry was assessed for sperm samples between the two methods of sperm recovery (collected with an AV or recovery via aspiration from the cauda epididymides of sacrificed rams), no morphometrical differences were observed. Significant differences were reported for the majority of the sperm motility traits (i.e. percentage motile, rapid-, medium-, slow swimming, curvilinear velocity (VCL), straight line velocity (VSL), average path velocity (VAP), and amplitude of the lateral head displacement (ALH)) recorded for ejaculated and epididymal sperm. The motility traits ALH and beat-cross frequency (BCF) analysed for epididymal sperm differed significantly between the two lines. When epididymal sperm were evaluated post-thaw, it became evident that the sperm obtained from the High Line rams had a larger acrosome surface cover when compared to that of the Low Line ram sperm. The addition of seminal plasma to epididymal samples did not result in an improvement of the preservation of sperm motility. It is known from the literature that cryopreservation causes a decrease in sperm head size. Head width was unaffected by cryopreservation with the addition of seminal plasma in this study, indicating a potential benefit with the use of seminal plasma in the cryopreservation protocol of epididymal ram sperm. The study compared two pre-processing techniques, i.e. the more time consuming swim-up technique (SUT) with a more time-efficient ‘flush technique’ (FT) to optimize the pre-processing protocol for motility assessment of sperm samples before cryopreservation of ram sperm. Comparison of the SUT and FT indicated that almost all of the motility parameters measured using the FT compared favourably with those obtained using the SUT. The results indicated that the FT can be used a more time-efficient technique to use for determining the motility of a sperm sample prior to cryopreservation. In conclusion, line differences associated with reproduction were observed in terms of the serving capacity of the rams, with selection for fecundity influencing the morphometric traits elongation and ellipticity for sperm obtained from the two lines. Future studies should be aimed at investigating morphometric traits of ovine sperm, to correlate it with fertilizing ability of sperm post-thaw and ensure optimal cryopreservation processing.
The influence of heat stress on the functionality of ovine spermatozoa
(Stellenbosch : Stellenbosch University, 2022-04) Stapelberg, Wian; Lambrechts, Helet; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: With the current trend in the global human population growth, the demand for animal production is predicted to increase significantly in the coming years. The increased demand for animal products will coincide with the period in which the world will experience changes in the global climate that will ultimately affect agricultural production. When considering the use of assisted reproductive techniques in the sheep industry, given the expected increase in average global temperatures, it is important to identify rams that produce spermatozoa that are resilient to temperature changes associated with the collection, processing, and preservation. This study aimed to determine the influence of scrotal insulation on sperm sample quality, and the resumption of normal spermatogenic activity in the testes of adult Dohne Merino rams, to potentially classify rams in terms of resilience to heat stress and its related effect on physiological processes such as spermatogenesis. Twelve rams formed part of the scrotal insulation phase, of which 10 rams were subjected to scrotal insulation. Two rams were not subjected to scrotal insulation and represented a Control group. The scrotal insulation devices were fitted after the first semen sampling, and thermographic measurements (Week 0), and remained fitted for 7 consecutive days. Semen samples and thermographic measurements were recorded after removal of the scrotal insulation devices, and thereafter every fortnight at Week 3, 5, 7, 9 and 11. The fitting of scrotal insulation devices in the present study proved to be effective in insulating the testes, as evident in the influence thereof on spermatogenic activity. There were no significant differences between the HR, LR, and Control groups for the percentage of abnormal and live spermatozoa over time during liquid storage (0-48h). There was a difference in the ability of spermatozoa from the rams to offer resilience to heat stress when the entire sampling period of 11 weeks was considered. Sperm morphology took 70 days to achieve pre-insulation values (below 40% for most rams), indicating that early spermatogenesis was most affected by heat stress. Considering the change in ambient temperature at Week 0 and Week 11 of the study as well as the different times of measuring scrotal temperatures during those weeks, scrotal temperatures took approximately 42 days to recover (18.64 ̊C – 24.84 ̊C), which coincides with the time it takes for spermatozoa to be produced from spermatogonia. By assessment of the change in iButton and scrotal temperatures, it was found that there were individual differences between rams, which indicates that certain rams are more efficient in thermoregulating testicular temperature than others. The study also aimed to determine whether a sperm hyperactivation functional test is effective in discriminating between Dohne Merino rams in terms of the resilience of their spermatozoa to heat stress. Semen samples were subjected to incubation at 38.5 ̊C for 30 minutes after the addition of 10mM procaine hydrochloride. Samples were evaluated at 0min, 15min, and 30min of incubation, and sperm viability, sperm morphology, and sperm acrosome integrity were quantified. There was no significant difference between the HR and LR groups for percentage live and abnormal acrosomes at all time intervals. There were significant differences between the HR and LR group for percentage abnormal spermatozoa at all time intervals. Significant individual differences were observed between the rams for sperm viability and morphology, but not for acrosome integrity when considering the entire 30 minutes of incubation. There was a faster rate in the reduction of quality for the LR group for abnormal spermatozoa compared to the HR group. The subpopulation structure of ejaculates should be considered when using induced hyperactivation as a sperm functional test, especially when ejaculation frequency is high. Simulations of the in-vivo environment of the female reproductive tract in an in-vitro environment may assist in more precise determination of fertilizing ability from heat stressed spermatozoa.
Ostrich (Struthio camelus) chick survival to 6 months post hatch : estimation of environmental and genetic parameters and the effect of imprinting, foster parenting and deliberate care
(Stellenbosch : Stellenbosch University, 2012-03) Wang, Magretha Diane; Cloete, Schalk W. P.; Dzama, Kennedy; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The South African Ostrich industry was established more than 100 years ago. Despite appreciable fluctuations and modifications in demand, the industry perseveres, with meat and leather as the current primary driving force. Low and variable early chick survival is globally considered as a major constraint in the industry. In spite of obvious welfare and production implications, research findings concerning ostrich chick survival are scant. Four studies involving chick survival to 24 weeks post hatch were thus performed. South African Black ostrich (Struthio camelus var. domesticus) data obtained from a commercial pair-bred ostrich flock maintained at the Oudtshoorn Experimental Farm, South Africa comprising 10418 records were utilized to run a series of single- and multiple-trait binomial analyses using either linear models (ASREML) or threshold models (Monte Carlo Markov Chain methods, employing Gibbs sampling software) respectively. Suitable fixed and random effect models together with variance and (co)variance components were derived from these analyses. Ostrich chick survival to 24 weeks post hatch was low (28%) with a large environmental component. Preincubation storage time only affected 0 to 3 week survival, while incubator had a significant effect on cumulative survival traits to 24 weeks as well as on 13 to 24 week survival. Female chicks outperformed males at 0 to 12 weeks, 0 to 24 weeks, 4 to 12 weeks and 13 to 24 weeks with regard to survival. Hen age was significant for all traits except survival during the first week as well as for survival from 13 to 24 weeks post hatch. All analyses exhibited comparable low heritability estimates for all survival traits except for 0 to 1 week survival and 13 to 24 week survival (h2 = 0.12 and 0.10; m2 = 0.08 and 0.07 respectively) which demonstrated higher additive genetic and maternal components when threshold models, using Gibbs sampling algorithms, were employed. Neither moisture loss nor day of external pipping exhibited notable additive genetic correlations with any of the estimated survival traits. Day-old chick weight demonstrated a low correlation with early chick survival (rg = 0.24 ± 0.19) with heavier chicks tending to have a higher survival probability. The effects of rearing method on early chick survival and growth were also investigated. Comparisons between chicks reared and fostered by adult ostriches in a semiextensive environment and chicks imprinted onto humans under an intensive system and between regular human handling in an intensive rearing system and the standard farm protocol of an intensive rearing system were made. No difference in the early chick survival to 3 weeks post hatch of chicks reared by foster parents and those chicks imprinted onto humans was demonstrated. At later ages, those chicks reared by foster parents outperformed human imprinted chicks. Human imprinted chicks exposed to regular handling demonstrate an enhanced early survival when compared to chicks exposed to conventional rearing protocol in intensive systems. The study is seen to provide guidance for further research on this topic.
Perceptions about commercial ostrich farming: views of consumers, farmers and secondary stakeholders
(Stellenbosch : Stellenbosch University, 2020-12) Snyders, Monique; Bonato, Maud; Cloete, Schalk W. P.; Engelbrecht, Anel; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: South Africa is the premier producer of ostrich products worldwide. The ostrich industry has recently come under scrutiny due to the global increased awareness of the welfare of production animals. This lucrative, niche market industry is not well known in most parts of the world and as a result of the public’s limited exposure to the ostrich industry and its husbandry practices, views and opinions about the industry and the welfare status of ostriches might be inadequate. However, the perceptions and opinions of the general public and specifically ostrich product consumers could increasingly determine the global market for ostrich products. This study aimed to determine the differences in knowledge, opinion and perceptions amongst consumers, farmers and secondary stakeholders in the ostrich industry with respect to ostrich production practices and the resulting welfare impact thereof. Participants were asked to complete a comprehensive survey, which firstly determined demographic factors – as these often influence the way in which a person’s opinion is expressed. Questions related to participants’ knowledge of ostrich farming followed; thereafter how important they perceive the impact of management and production aspects on the welfare of ostriches, and the potential impact of welfare aspects on buying decisions. Farmers and secondary stakeholders in the industry were specifically asked about their preferences regarding husbandry practices implemented on-farm and the perceived welfare impacts thereof. Most answers in the survey were scored on a scale of 1 to 5, from least to most important/likely/knowledgeable or from a highly negative to highly positive impact. The main results of this study highlighted a significant lack of knowledge about the ostrich industry and associated production practices, amongst consumers and specifically women and the youth. Generally, all participants agreed on the importance of basic needs (feed, water, health) for the well-being of ostriches. Significant emphasis was placed on natural rearing and husbandry practices as it appears that consumers, women, vegetarians and highincome participants, prefer production animals to be reared in environments that resemble their natural habitat. Importance was also placed on the level of knowledge and skill of stockmen involved in the industry. It appeared that specifically women and vegetarian participants placed a high value on the general welfare of farmed ostriches, while ostrich farmers emphasised the welfare of animals destined for slaughter in order to maintain product quality. Consumers indicated that there is a need to implement a formal welfare protocol for commercial ostrich production. Farmers preferred artificial rearing and incubation/hatching practices with human assistance (when necessary) and they placed emphasis on the importance of product quality when compared to secondary stakeholders. It was also evident that farmers more readily preferred welfare conscious production practices in contrast to the preference for welfare neutral or even potentially compromising production practices by secondary stakeholders. Farmers showed their preference for frequent visual inspection of birds and seemed to score the importance of the welfare of ostriches for product quality higher than stakeholders. Furthermore the transportation and relocation of birds was identified as a potential welfare problem in the industry. Farmers were also less likely to promote the introduction of ostrich-specific welfare protocols on-farm than stakeholders in the industry. The results of this survey aided in identifying potential welfare problems in the ostrich industry and could form the basis of future work for the development of a welfare protocol for the commercial farming of ostriches. Some considerations for welfare indicators and measures have been developed stemming from the results of this study (Appendix G). Further studies could investigate the effect of different handling and transportation practices on the well-being of commercially farmed ostriches. This study thus emphasizes the need for a formal welfare protocol or “Code of best practices” for the commercial farming industry as this will improve product quality and transparency and will also enable farmers to promote the welfare of ostriches produced for slaughter.
Studies on the environmental and genetic parameters for lamb survival, growth and wool traits of the Elsenburg Dormer and SA Mutton Merino flocks
(Stellenbosch : Stellenbosch University, 2020-12) Muller, Anieka; Cloete, Schalk W. P.; Brand, T. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Environmental and genetic parameters and trends of the Elsenburg South African Mutton Merino (SAMM) and Dormer resource flocks were estimated. The breeds were also compared for lamb survival, growth, wool, carcass and meat quality traits. Early growth and lamb survival data over a 64-year period (1955 - 2019) and yearling weight and wool data over a 36-year period (1983 - 2019) were used in the study for SAMM sheep. Single-trait heritability estimates of SAMM lambs amounted to 0.07 for birth weight (BW), 0.03 for weaning weight (WW), 0.02 for lamb survival (LS), 0.24 for yearling weight (YW), 0.58 for clean yield (CY), 0.37 for clean fleece weight (CFW), 0.34 for staple length (SL), 0.55 for coefficient of variation of fibre diameter (CVFD) and 0.68 for fibre diameter (FD). Maternal heritability estimates were 0.15 for BW, 0.06 for WW and 0.01 for LS. Multi-trait heritability estimates compared well with the single-trait estimates. Genetic correlations among weight traits ranged from 0.04 for BW and YW to 0.81 for WW and YW. Low to moderate correlations among yearling traits accorded with previous literature for wool breeds. Genetic trends showed favourable but extremely slow genetic responses. Data from 1943 to 2019 were used to investigate genetic and environmental parameters and trends for early growth traits and LS in the Dormer flock. Yearling live weight- and wool traits were recorded for a shorter period from 2008 to 2018. Direct single-trait heritability estimates were 0.15 for BW, 0.06 for WW, 0.02 for LS, 0.19 for YW, 0.63 for CY, 0.56 for CFW, 0.59 for SL, 0.59 for SS, 0.60 for CVFD and 0.80 for FD. Maternal genetic effects amounted to 0.21 for BW, 0.08 for WW and 0.06 for YW. Genetic correlations among live weight traits ranged from low (-0.11) between BW and YW to very high (0.93) for WW and YW. Genetic correlations among wool traits were mostly low. Genetic trends for all weight traits suggested significant positive trends with time. Expressed relative to the overall phenotypic mean, these trends amounted to 0.12% for BW, 0.16% for WW and 0.45% for YW. Selection from 2013 for direct-, maternal- and a combination of direct and maternal breeding values up to 2019 resulted in genetic trends amounting to 0.07% for BW, 0.79% for WW and 1.01% for YW in the line selected on direct breeding values for WW. Corresponding genetic trends amounted to respectively -0.51%, 0.17% and 0.27% in the line selected on maternal breeding values for WW and respectively -0.20%, 0.41% and 0.58% in the line selected for a combination of direct and maternal breeding values. Maternal genetic trends were markedly smaller in magnitude even in those lines were selection was based on maternal breeding values. Results indicated that SAMM lambs were heavier at birth compared to their Dormer contemporaries (4.19 vs. 4.13 kg). Dormers were heavier than SAMMs at weaning (27.3 vs. 25.0 kg) and also when weighed as yearlings (49.7 vs. 47.8 kg). Dormer lambs had a higher survival rate than SAMM lambs at 0.89 and 0.81, respectively. Clean fleece weight was the only wool trait not affected by breed. Dormer yearlings had a higher CY and SL than SAMM yearlings. In contrast, SAMM yearlings had a lower CVFD and finer wool than their Dormer contemporaries (respectively 22.4 vs. 28.6 μm). The two breeds did not differ for slaughter weight, carcass weight or dressing percentage. Dormers had a thicker subcutaneous fat cover at the rump than SAMM contemporaries (5.00 vs 4.18 mm). It was concluded that all traits considered were variable and heritable, although selection responses to traits such as lamb survival and weaning weight in SAMMs may be slow. Breed differences for economically important traits were consistent with the roles of the two breeds, with the Dormer as a coarse-woolled terminal sire breed and the SAMM as a dual-purpose breed.
Studies on the genetics of ovine behaviour in a Western Cape resource flock aimed at improving animal welfare
(Stellenbosch : Stellenbosch University, 2019-04) Burger, Marelee; Cloete, Schalk W. P.; Dzama, Kennedy; Cloete, J. J. E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: Data were collected on a Merino resource flock on the behaviour of ewes and lambs from 1993 to 2002. This flock was divergently selected from the same base population since 1986 for the number of lambs weaned per mating (NLW). Selection resulted in two selection lines, namely the High line (H line, upward selection for NLW) and the Low line (L line, downward selection for NLW). Additionally, the effect of these behaviours and selection lines were reported for NLW and lamb survival, as a key welfare indicator trait. Data from arena behaviour on Merino weaners were also collected over a 15-year period using the same resource population divergently selected for NLW. Ram lambs, progeny of mature ewes and singles were heavier at birth than ewe lambs, progeny of young and old ewes and multiples respectively. H line lambs had shorter lengths of parturition than L line lambs, where this difference was also found in H line and L line ewes. The effects of dam age were significant for the latency from birth to suckling as it improved with ewe age, and in both ewe and lamb studies H line ewes had better maternal cooperation scores than L line ewes. Maternal cooperation also had a significant effect on the latency for the lamb to progress from birth to suckling and maternal cooperation score improved with age in ewes. H line ewes had an improved NLW compared to L line ewes while H line lambs had a better survival. For production traits, H line lambs derived from embryo transplants were heavier at yearling age, had a lower fibre diameter, less wrinkles at the neck, body, breech and overall when compared to L line lambs. Survival of lambs reared by surrogate dams was higher in the H line than in the L line. Single-trait direct heritability estimates (h²) in lambs were 0.15 for birth weight, 0.07 for lamb survival, 0.06 for length of parturition, 0.12 for latency from birth to suckling and 0.00 for maternal cooperation score. Direct heritability estimates, assessed as trait of the ewe, were 0.04 for NLW, 0.17 for length of parturition, 0.07 for maternal cooperation score and 0.20 for the interval ewes remained on or near their lambing sites. Genetic trends suggested divergence between the lines for breeding values for length of parturition, suggesting that parturitions became shorter in the H line and longer in the L line. The results and parameter estimates obtained, suggested that selection for improved NLW would yield desirable outcomes for ewe behavioural traits. Maternal permanent environment variance ratios (c²) were 0.07 for lamb survival and 0.17 for maternal cooperation score. Survival of the lamb was favourably correlated to the length of parturition and maternal behaviour score on the genetic level. It was evident that neonatal behaviour was, to an extent, under genetic control in paddock-reared sheep. In the arena test, animals from the H line approached closer to stationary human seated between the test animal and its flock mates and had fewer urination and defecation events than their L line contemporaries but travelled longer distances in the arena. The distance the lambs maintained from the human operator (0.08), urinating events (0.13), and defecating events (0.04) were all lowly heritable. However, the number of lines crossed (0.22) and the number of bleats (0.35) were moderately to highly heritable. Selection for NLW and certain neonatal and perinatal ewe behaviours would benefit the welfare of ewes and lambs. From the arena test it was also evident as H line lambs experienced lower levels of stress in the contrived area environment.
Studies on the response of lambs and ewes to changes in the ambient climate owing to climate change
(Stellenbosch : Stellenbosch University, 2022-12) Steyn, Shannong; Cloete, Schalk W. P.; Brand, T. S.; Van Zyl, Johan Hendrik Combrink ; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: This study investigated the impact of climate instability on neonatal lamb behaviour as a proxy for lamb survival in a winter lambing season in the Western Cape, as well as the impact of increased temperatures on heat stress indicator traits in mature ewes in the Western and Eastern Cape. Historic data were used to establish the relationship of neonatal lamb behaviour with cold stress and to derive genetic parameters for early lamb behaviour. Merino lambs of the Elsenburg flock were phenotyped for behaviour latencies from birth to first standing (LTBS) and from standing to first suckling (LTSS). These data were analysed in relation to a cold stress gradient (CSG) derived from a combination of wind, rain, and temperature. The flock consisted of a line selected for number of lambs weaned per ewe mated (NLW; the High or H-Line) and a line selected against NLW (Low or L-Line). H-line lambs progressed faster from standing to first suckling than L-line lambs. Increased CSG-levels resulted in 18% faster progress in LTBS when mild conditions at 800kJm⁻²h⁻¹ were compared to stressful conditions at 1200kJm⁻²h⁻¹. LTSS was compromised by 76.0% as CSG-values increased from 800kJm⁻²h⁻¹ to 1200kJm⁻²h⁻¹. Heritability estimates were 0.22 for LTBS and 0.06 for LTSS. The maternal heritability for LTBS was 0.06 and the dam permanent environment variance ratio 0.09 for LTSS. The traits were not genetically correlated. Further research is required to understand the responses of lambs to cold stress. Average temperatures are likely to increase, resulting in hotter and dryer conditions in South Africa. The impact of these changes on animal production and welfare is not well-defined. Three trials were conducted on 10 to 20 mature, dry ewes at 2 locations to determine the homeothermic response of nine sheep breeds between 2016 and 2022. These breeds were the Dohne, Dormer, Dorper, Ile de France, Meatmaster, Merino, Namaqua Afrikaner, South African Mutton Merino (SAMM) and White Dorper. They were studied in different combinations across trials. On days forecast to be hot at noon, animals were assessed under cool conditions in the morning and hot conditions at noon/afternoon by monitoring individual rectal temperature, eye temperature (thermal imaging), spot temperature, and respiration rate. The increased heat in the afternoon sessions markedly increased all traits across trials. In general, hair breeds (Dorper, White Dorper, Meatmaster, and particularly Namaqua Afrikaner) were able to maintain lower basal respiration rates compared to the wool breeds originating from temperate regions (Dohne, Dormer, Ile de France, Merino, and SAMM). These results suggest that hair sheep and hardy indigenous breeds such as the Namaqua Afrikaner may cope better with the anticipated higher heat load in the future when compared to the breeds originating from temperate regions. Rectal temperature was low- moderately repeatable across trails, while outcomes for respiration rate and spot temperature were more variable and commonly affected by the reranking of ewes across sessions as well. Eye temperature was not repeatable. There is still marked scope for research on ovine adaptation to heat stress conditions in South Africa.
Sustainable management of breech flystrike in sheep by manipulating tail length: the effect of tail docking on lamb welfare as well as the genetics of ovine tail length
(Stellenbosch : Stellenbosch University, 2024-03) Teubes, Megan; Cloete, Schalk W. P. ; Dzama, Kennedy; Scholtz, Ansie; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
ENGLISH ABSTRACT: It is expected that society will place more pressure on animal production systems to implement change, given increased awareness of ethical animal husbandry and global sustainability. Increased temperatures, due to climate change, are likely to provide favourable conditions for insect activity, thereby inducing favourable conditions for blowfly activity. Myasis following on the deposition of eggs by gravid females of the Australian sheep blowfly, Lucilia cuprina, in the breech area of Merino sheep compromises animal welfare and results in high production losses. Tail docking is a commonly accepted way to render lambs less attractive to breech flystrike as adult sheep, by reducing dag formation in the breech area. This procedure is considered as invasive and painful, with an immediate impact on lamb welfare. Therefore, this study assessed the degree of discomfort lambs experienced both during tail docking and after the procedure was conducted. A total of 228 lambs were randomly assigned to a treatment group whose tails were docked with a hot-blade and a control group where lambs were left intact after tail length was measured. Behavioural assessment of the two groups during tail docking recorded higher (P < 0.05) levels of agitation and vocalisation in the treatment group, while the control group were more likely to be calm. These behavioural patterns persisted in the post-procedural phase with no differences (P > 0.05) between recordings 2 or 10 minutes after docking. The second objective was to determine if there is sufficient genetic variation to select Merino sheep for shorter tail length, on the assumption that selection for shorter tails may provide the same benefits as docking without the painful docking procedure. Tail length had a moderate heritability of 0.30 ± 0.08 with a small maternal effect (0.08 ± 0.04) and nonsignificant permanent dam environmental effect. However, selection for shorter tails will reduce the size of lambs if breeding values are not adjusted for skeletal size by including docking weight as a covariate when breeding values are estimated. The final objective of the study was to assess the effect of breeding for shorter tails on other production traits by estimating genetic correlations between tail length and hogget traits. Tail length was genetically correlated to clean fleece weight (0.36 ± 0.18) and total wrinkle count (0.33 ± 0.15). Selection for a reduced tail length may thus compromise fleece weight and result in plainer (less wrinkly) sheep. The latter genetic correlation is favourable, given the well-recorded higher predisposition of wrinkly sheep to breech strike. It was concluded that tail docking results in at least temporary discomfort in young lambs, thereby compromising their welfare. This procedure could potentially be replaced by selection for shorter tails. However, the reduction of tail length to levels where breech strike is expected to be minimised may take several decades.
Ultrasound scanning and body condition scoring as aids to reproduction management of sheep
(2022-04) Geerkens, Willem Hendrik; Brand, T. S.; Cloete, Schalk W. P.; Van Zyl, Johan Hendrik Combrink ; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
ENGLISH ABSTRACT: The body condition scoring (BSC) and ultrasound scanning of ewes with reference to their reproductive performance are management tools with potential to ease the management, nutrition and breeding of South African sheep. There is a paucity of data on condition scores and scanning figures of individual sheep in the local ovine genetic resource and relevant data were thus sourced from genetic resource flocks managed by science and research institutions. Data from the Elsenburg Merino, Dormer and South African Mutton Merino (SAMM) flocks were used to study genetic and environmental parameters for ewe mating weight, BCS at mating and lambing, as well as for correlations of these traits with reproduction. H Line Merino ewes were heavier than the L Line at mating, but no line differences were found for condition scores. The H Line was selected for reproduction while the L Line was selected against reproduction. Dormer ewes were heavier than SAMM ewes at mating, with the SAMM having higher condition scores. Ewe mating weight was highly heritable at 0.74 in Merinos, with lower estimates for BCS at mating (0.28) and lambing (0.18). Ewe mating weight was moderately heritable at 0.49 in Dormers and SAMMs, with lower estimates for BCS at mating (0.21) and lambing (0.27). Genetic correlations among these traits were positive and moderately high for all flocks, ranging from to 0.58 to 0.93. Genetic correlations of mating weight and condition scores with reproduction were mostly negative (i.e. unfavourable) across ewe age groups and analyses, significantly so in some cases. The unfavourable genetic correlations are probably related to complex interactions of age and current and previous reproduction in mature ewes, as well as the relationship of reproduction with BCS being characterised by an intermediate optimum. Further studies are indicated. On the other hand, ultrasound scanning was studied in Dohne Merino and SAMM ewes of the Mariendahl flock. Lambing year had a significant effect on all reproductive traits with values oscillating in both breeds. Number of embryos lost per ewe present at lambing was generally low (0.00 to 0.05). Number of lambs scanned per ewe available was moderately repeatable at 0.11 to 0.16, depending on breed and modelling. A comparable range of 0.16 to 0.19 was found for number of lambs born per ewe lambed. Repeatability estimates for embryonic losses were not significant. Scanning and lambing rate were highly correlated on the ewe level, suggesting that scanning figures would act as a good proxy for lambing rate in the absence of complete lambing data. Both ewe BCS and the outputs of ultrasound scanning may have a role to play in managing reproductive performance at the flock level. However, further refinement is needed before these managerial aids can be used with confidence in the broader South African sheep flock.

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