Browsing by Author "Cloete, S. W. P. (Schalk Willem Petrus van der Merwe)"
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- ItemA comparison between the body composition, carcass characteristics and retail cuts of South African Mutton Merino and Dormer sheep(2004) Cloete J.J.E.; Hoffman L.C.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Fourie J.E.The body composition, carcass characteristics and retail cuts of 61 Dormers (21 rams and 40 ewes) and 35 South African Mutton Merinos (SAMM) (17 rams and 18 ewes) were determined. A range of carcass measurements was recorded. Since there was no sex x breed interaction, only main effects of breed and sex were considered. There were no differences in slaughter weight between Dormer and SAMM sheep at 18 months of age. Dormers had a 2.7% point higher dressing percentage and a 6.2% higher carcass weight than the SAMM. The Dormer had a higher fat content (kidney fat, back-fat depth) than the SAMM. The eye-muscle area of the Dormers was 13% larger than that of the SAMM sheep. Rams were heavier than the ewes at slaughter. All the traits measured, indicated advantages in favour of rams. Only the saturated, monounsaturated fatty acids and polyunsaturated fatty acids to saturated fatty acids ratio differed significantly between the Dormer and SAMM sheep. Based on the fatty acid profile, SAMM meat is slightly healthier than that of Dormer sheep. The higher retail cut weights of Dormers suggested that they were superior to the SAMM as far as meat production was concerned.
- ItemA preliminary study on the application of image analysis for the measurement of ostrich eggshell traits(2006) Cloete Jr. S.W.P.; Scholtz A.J.; Brand Z.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe)Embryonic mortality in developing ostrich embryos has been linked to water loss in eggs during artificial incubation. Traits possibly related to water loss were assessed on shell samples obtained from 512 hatched ostrich eggs. Moderate to high repeatability estimates (0.43 to 0.86) were derived from significant between female variance components for all traits. Two-trait between female correlations were unity or near unity when the same trait was assessed at either the side or the top of individual eggshells. Recordings at either site can thus be considered as the same on the level of the individual female, implying that in future studies only one measurement is needed during the evaluation of the traits investigated in this study. © South African Society for Animal Science.
- ItemA study of phenotypic and genetic aspects of reproduction rate in the Tygerhoek Merino flock(Stellenbosch : Stellenbosch University, 1986) Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Stellenbosch University. Faculty of . Dept. of .
- ItemAcross flock genetic parameter estimation for yearling body weight and fleece traits in the South African Dohne Merino population(South African Society for Animal Science, 2008) Van Wyk, J. B.; Swanepoel, J. W.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Olivier, J. J.; Delport, G. J.Accurate genetic parameter estimates are needed upon which to perform multiple-trait across flock breed analyses. Genetic parameters for yearling body weight (BW), clean fleece weight (CFW) and mean fibre diameter (MFD) were estimated using records of 107 389 individuals (the progeny of 1 530 sires and 45 178 dams) collected between 1992 and 2004 in the South African Dohne Merino population. Fixed effects included in the model were flock-year-season-sex- management group (1 594 classes), type of birth (singles, multiples), age of dam (2 - 7+ years) and age at measurement, fitted as a linear covariate (385 ± 12 days). Six different single-trait animal models were fitted, where different combinations of the following random effects were fitted: direct additive, the sire-flock interaction, the sire-flock-year-season interaction (SFYS), the dam genetic effect, the direct-maternal correlation and the dam permanent environmental effect. These analyses were followed by a three-trait analysis structured according to the log likelihood ratios obtained for the single-trait analysis. This analysis allowed the calculation of relevant correlations among traits together with their respective standard errors. Direct heritability estimates from the three-trait analysis were 0.17 for BW, 0.19 for CFW and 0.45 for MFD. Maternal heritability estimates were 0.01 for BW and 0.006 for CFW, with corresponding dam permanent environmental ratios of respectively 0.03 and 0.02. The genetic correlation between animal effects amounted to 0.48 for BW. Derived proportions of the total phenotypic variance due to SFYS were 0.02, 0.02 and 0.02, respectively. Genetic correlations of BW with CFW and MFD were 0.11 and 0.13, respectively, and of CFW with MFD 0.16. It was concluded that the inclusion of some form of a genotype by environmental interaction as part of the national evaluation is essential, although it controlled only a modest portion of the overall phenotypic variation.
- ItemThe adaption of the South Africa sheep industry to new trends in animal breeding and genetics : a review(South African Society for Animal Science, 2014-10-11) Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Olivier, J. J.; Sandenbergh, L.; Snyman, M. A.The history of sheep breeding research in South Africa can be divided roughly into four eras, namely the research and development phase, the commencement of recording and evaluation, the expansion of recording schemes, and, most recently, the adaptation of schemes to international benchmarks. The most recent era has presented scientists with the greatest challenges, namely the inclusion of genomic breeding values in routine sheep recording and of disease-resistance traits during routine evaluation. The establishment of reference populations for the major South African sheep breeds to estimate genomic breeding values is an immediate challenge. This process may be facilitated by a number of genetic resource flocks that are phenotyped for traits that are not routinely recorded in the national evaluation. A limited number of these animals are also genotyped. There is strong evidence that resistance of sheep to external and internal parasites is heritable, and may be improved by purposeful selection. Efforts should be concentrated on the inclusion of disease resistance traits in national analyses where appropriate. However, seen against the background that South African investment in research is appreciably less than in developed countries, lack of funding and high-capacity manpower may impede rapid progress. There thus seem to be many challenges for future generations of sheep breeding scientists.
- ItemCarcass and muscle yields of ostriches as influenced by genotype(South African Society for Animal Science, 2007) Hoffman, L. C.; Brand, M. M.; Muller, M.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe)ABSTRACT: Live, carcass, leg and muscle weight (kg) as well as dressing percentage were compared between South African Black (Struthio camelus var. domesticus) ostriches, purebred Zimbabwean Blue Neck (Struthio camelus australis) ostriches and the progeny of Zimbabwean Blue Neck males crossed with South African Black females, commercially slaughtered at 14 months of age. South African Black ostriches had the lowest live (84.9 kg) and carcass (43.3 kg) weights, compared to Zimbabwean Blue Necks (100.9 and 51.2 kg, respectively). In general, crossbred birds resembled Zimbabwean Blue Necks more closely for the quantitative meat traits. However, dressing percentage (51.1%) and yields of different carcass components (bone, leg) did not differ between genotypes. Six of the major muscles present in the ostrich leg (M. gastrocnemius, M. femorotibialis accessorius, M. iliotibialis cranialis, M. iliotibialis lateralis, M. iliofibularis and M. iliofemoralis) showed significant weight differences between genotypes, with South African Black ostriches yielding the lowest values.
- ItemA comparison between the body composition, carcass characteristics and retail cuts of South African mutton Merino and Dormer sheep(South African Society for Animal Science, 2004) Cloete, J. J .E.; Hoffman, L. C.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Fourie, J. E.The body composition, carcass characteristics and retail cuts of 61 Dormers (21 rams and 40 ewes) and 35 South African Mutton Merinos (SAMM) (17 rams and 18 ewes) were determined. A range of carcass measurements was recorded. Since there was no sex x breed interaction, only main effects of breed and sex were considered. There were no differences in slaughter weight between Dormer and SAMM sheep at 18 months of age. Dormers had a 2.7% point higher dressing percentage and a 6.2% higher carcass weight than the SAMM. The Dormer had a higher fat content (kidney fat, back-fat depth) than the SAMM. The eye-muscle area of the Dormers was 13% larger than that of the SAMM sheep. Rams were heavier than the ewes at slaughter. All the traits measured, indicated advantages in favour of rams. Only the saturated, mono-unsaturated fatty acids and polyunsaturated fatty acids to saturated fatty acids ratio differed significantly between the Dormer and SAMM sheep. Based on the fatty acid profile, SAMM meat is slightly healthier than that of Dormer sheep. The higher retail cut weights of Dormers suggested that they were superior to the SAMM as far as meat production was concerned.
- ItemDead-in-shell positions of near-term ostrich embryos(South African Society for Animal Science, 2016-12-06) Brand, Z.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Malecki, I. A.; Brown, C. R.The patterns of embryonic development in ostriches, especially in the last stage of hatching, are still not well understood. This study examined between 3468 and 3484 dead-in-shell (DIS) eggs with chicks that died between day 35 and day 42 of artificial incubation. Most DIS chicks were positioned correctly with their heads towards the air cell (52.6%). DIS chicks that positioned their heads near the equator of the egg amounted to 46.5%, while a small percentage (0.9%) were positioned with their upper body towards the bottom of the egg. More DIS chicks tended to pip internally near the equator of the egg (37.6%) than DIS chicks that pipped internally through the membranes into the air cell (34.4%). Most DIS chicks had their heads turned in the correct position from left to right (54.4%), though their beaks were mostly positioned towards the air cell (52.9%). The highest percentage of DIS chicks had their feet in the upwards position (52.4%), while 46% had their feet across or below the head. The wings of all DIS chicks were positioned next to the body. Results from the study showed that most of the DIS chicks were roughly in the correct position, but were still unable to hatch. This warrants future research to investigate the reasons that prevent correctly positioned chicks from hatching.
- ItemThe effects of dietary energy and protein concentrations on ostrich skin quality(South African Society for Animal Science, 2006) Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Van Schalkwyk, S. J.; Brand, T. S.; Hoffman, L. C.; Nel, C. J.ABSTRACT: The effects were investigated of energy and protein concentrations (with associated amino acid concentrations) in ostrich diets on leather quality of the skins of 50 ostriches. Energy concentrations were 9.0, 10.5 and 12.0 MJ ME/kg diet and protein concentrations were 130, 150 and 170 g/kg diet. The physical leather parameters that were assessed included tensile strength, elongation, slit tear strength and skin thickness. All traits were assessed in samples taken parallel or perpendicular to the spine in the butt region of the slaughter bird. The raw skin weights of ostriches consuming the diets with energy concentrations of 10.5 and 12.0 MJ ME/kg diet were respectively 19.4 and 21.8% heavier at slaughter than those of their contemporaries on the 9.0 MJ ME/kg DM diet. A corresponding trend was found for trimmed skin weight, and the increase in skin weight with diets higher in energy exceeded 10%. Differences between skin area means only approached significance, with a tendency to increase with an increased energy concentration. Leather thickness taken parallel to the spine was increased by 13% in the diet containing 12 MJ ME/kg diet, compared to the diet containing 9.0 MJ ME/kg. Dietary protein concentrations failed to influence skin weight, skin area or any of the physical leather properties. The skins of male ostriches were thicker than those of females. The study suggested that the lowest levels of energy and protein supplied, were sufficient to prevent a decline in physical leather quality.
- ItemEnvironmental and genetic factors affecting faecal worm egg counts in Merinos divergently selected for reproduction(South African Society for Animal Science, 2015-12-09) Mpetile, Z.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Kruger, A. C. M.; Dzama, K.Infestation with gastrointestinal nematodes is probably among the most pervasive problems in small-stock production worldwide. Faecal worm egg count (FWEC) has been reported as an indirect measure of parasite resistance in livestock production. Environmental and genetic factors of FWEC were assessed, using data from Merino sheep that were selected divergently for reproductive performance at Elsenburg Research Farm. Data consisted of animals born in 1995 - 1996, 1999, and 2001 - 2013. Two datasets were considered: 1869 FWEC records of animals born in the years provided above, and 851 records of the divergently selected lines and the reciprocal cross between them, born in 2003 - 2008. Rectal faecal sample grabs were obtained from individual animals after drenching had been withheld for approximately 6 to 10 weeks, generally in April. Nematode eggs in these samples were counted using the McMaster technique, with a sensitivity of 100 eggs/g wet faeces. The fixed effect of birth year x sex interaction was significant, with rams showing higher mean values for FWEC than ewes in most years, but these results were not consistent. FWEC showed significant but low heritability, estimates ranging from 0.06 for untransformed data to 0.10 for log-transformed data, suggesting that selection for low FWEC could be slow. There was no hybrid vigour and compelling evidence of genetic change in log-transformed FWEC in either line, suggesting a negligible genetic correlation between FWEC and reproduction. In this experiment, the researchers studied animals that had been exposed to parasite challenge in autumn. Therefore, the results of this study cannot be applied directly to a situation in which faecal samples were collected in other seasons. Future work is needed to determine the effect of season on the heritability of parasite resistance in South African conditions.
- ItemEvaluation of subjectively assessed nodule traits of ostrich skins as influenced by slaughter age(South African Society for Animal Science, 2005) Van Schalkwyk, S. J.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Hoffman, L. C.; Meyer, A.ABSTRACT: Ostrich skins (n = 214) were assessed by 28 participants involved in the ostrich leather production and marketing chain. The participants were from various sectors in the ostrich industry, including producers, skin graders, leather marketers, agents and process managers. Skins were evaluated during two occasions, firstly without any knowledge of slaughter age and thereafter with prior knowledge of slaughter age. Nodule acceptability and distribution for each skin were scored on a linear scale of 1 to 10. Slaughter age, as estimated by the participants during the first evaluation, was regressed on the actual age of the birds at slaughter. The derived regression indicated that actual slaughter age accounted for approximately 46% of the variation found in estimated slaughter age. Nodule acceptability scores generally increased with slaughter age. Average scores of at least moderately acceptability were found only in skins from birds slaughtered at 11 months of age and older. A corresponding trend with increase in slaughter age was found for nodule distribution scores. Between skin variance ratios were comparatively low for nodule acceptability (0.09-0.10, depending on prior knowledge of slaughter age or not) and nodule distribution (0.05-0.06). The between scorer variance ratio was generally higher, exceeding 0.35. Scores for nodule acceptability with or without prior knowledge of the age of individual skins at slaughter were essentially the same, as judged from a near unity covariance ratio between individual skins. A similar trend was observed for nodule distribution score. The need for practical methods for the objective assessment of the acceptability of nodules and ostrich leather quality was expressed.
- ItemEvaluation of the OvineSNP50 chip for use in four South African sheep breeds : short communication(South African Society for Animal Science, 2016) Sandenbergh, L.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Roodt-Wilding, R.; Snyman, M. A.; Bester-Van Der Merwe, A. E.Relatively rapid and cost-effective genotyping using the OvineSNP50 chip holds great promise for the South African sheep industry and research partners. However, SNP ascertainment bias may influence inferences from the genotyping results of South African sheep breeds. Therefore, samples from Dorper, Namaqua Afrikaner (NA), South African Merino (SA Merino) and South African Mutton Merino (SAMM) were genotyped to determine the utility of the OvineSNP50 chip for these important South African sheep breeds. After quality control measures had been implemented, 85 SA Merino, 20 Dorper, 20 NA and 19 SAMM samples remained, with an average call rate of 99.72%. A total of 49 517 (91.30%) SNPs on the chip met quality control measures and were included in downstream analyses. The NA had the fewest polymorphic loci, 69.20%, while the SAMM, Dorper and SA Merino had between 81.16% and 86.85% polymorphic loci. Most loci of the SA Merino, Dorper and SAMM had a MAF greater than or equal to 0.3. In contrast, the NA exhibited a large number of rare alleles (MAF < 0.1) and a uniform distribution of other loci across the MAF range (0.1 < MAF ≤ 0.5). The NA exhibited the least genetic diversity and had the greatest inbreeding coefficient among the four breeds. The results of the Dorper, SA Merino, and SAMM compare favourably with those of international breeds and thus demonstrate the utility of the OvineSNP50 chip for these breeds. Effects of SNP ascertainment bias, however, could be seen in the number of non-polymorphic loci and MAF distribution of the three commercial breeds in comparison with those of the NA. The implementation of methods to reduce the effect of SNP ascertainment bias and to ensure unbiased interpretation of genotype results should therefore be considered for future studies using OvineSNP50 chip genotype results.
- ItemAn exploratory analysis to determine the impact of fixed effects and to establish genetic parameters across six types of ostrich feathers(South African Society for Animal Science, 2015-02-24) Brand, Z.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe)After a decline in value, ostrich feathers have again become an important part of the income of ostrich producers. Between 22586 and 22753 feather weights, as well as length and width measurements, were obtained from feathers harvested annually during the resting period from a pair-bred ostrich flock maintained at Oudtshoorn Research Farm from 2001 to 2012. The flock consisted mostly of the South African Black (SAB) genotype, but birds from the Zimbabwean Blue (ZB) and Kenyan Redneck (KR) strains were also introduced to study strain effects, as well as the effect of crossbreeding between these genotypes (ZB x SAB; SAB x ZB; KR x SAB; SAB x KR). The feathers were sorted into six feather-type categories, namely floss, short hard body feathers, long hard body feathers, tail feathers, white plumes and short body floss. White plumes had the highest average feather length (AFL), average feather width (AFWD) and square-root-transformed feather weight (SRFW) at 66.2 ± 0.38 cm, 21.2 ± 0.23 cm and 13.66 ± 0.17 g, respectively. A significant decline in AFL took place from 2001 and 2012 (40.0 ± 0.25 cm and 38.7 ± 0.56 cm, respectively), while AFWD stayed fairly constant. Feather weights were higher for males than females resulting in a 24% higher geometric mean for backtransformed feather weights (GMFW) for males relative to females. SAB birds outperformed ZB and KR birds for AFL, AFWD and SRFW. Crosses were intermediate and sometimes comparable with the SAB genotype. Except for long hard body plumes, the weights for all the feather types were higher for the purebred SAB breeders compared with purebred ZB and KR breeders. Heritability estimates of AFL, AFWD and SRFW across the six feather categories were low to moderate at 0.080 ± 0.012, 0.044 ± 0.009 and 0.116 ± 0.017, respectively. The animal permanent environmental effect for the feather traits was lower in magnitude and ranged between 0.025 ± 0.008 for AFL and 0.041 ± 0.012 cm for SRFW. Direct genetic correlations of feather dimensions with SRFW were moderate to high at 0.287 ± 0.117 with AFL and 0.614 ± 0.072 with AFWD. The present results indicate that feather quantity can be improved by genetic selection in ostriches, and further studies should be conducted.
- ItemThe fatty acid composition of muscles and fat depots of ostriches as influenced genotype(South African Society for Animal Science, 2012) Hoffman, L. C.; Brand, M. M.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Muller, M.Three genotypes of ostrich (South African Black, Zimbabwean Blue Necks and crosses between Zimbabwean Blue Neck males x South African Black females) were used to investigate the influence of genotype on the fatty acid composition of the musculus gastrocnemius and musculus iliofibularis, and abdominal and breast fat depots. Total saturated fatty acids in both the m. gastrocnemius and m. iliofibularis were higher in crosses (36.4% and 35.9%) than in South African Black ostriches (32.9% and 30.4%), whereas mono-unsaturated fatty acids were highest in South African Black ostriches. Total polyunsaturated fatty acids in the m. gastrocnemius were lowest in South African Black ostriches (26.5%) compared with the Zimbabwean Blue Necks (33.2%). Neither the ratio of polyunsaturated to saturated (0.73 to 0.99) nor n-6 to n-3 (1.6 to 2.2) fatty acids were influenced by genotype, although the ratio of polyunsaturated to saturated fatty acids in Zimbabwean Blue Necks was higher in the m. gastrocnemius (0.99) than in the m. iliofibularis (0.73). Differences in individual fatty acids were prominent in the breast fat, and total saturated and mono-unsaturated fatty acids differed between genotypes in both breast and abdominal fat. Only the ratio of polyunsaturated to saturated fatty acids in the fat depots differed between South African Black (0.48) and Zimbabwean Blue Neck ostriches (0.42). The latter ratio was higher in the breast (0.50) than abdominal (0.42) fat in Zimbabwean Blue Necks. These results indicate that crossbreeding of different genotypes of ostriches reared under similar conditions does influence the overall fatty acid profiles of meat and fat.
- ItemFertility in dairy cows and ways to improve it(South African Society for Animal Science, 2018-11-17) Muller, C. J. C.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Botha, A.The fertility of dairy cows affects the genetic improvement and financial sustainability of dairy herds. Fertility is a complex trait that is affected by several factors. Genetically, fertility is difficult to improve because of low heritability. Cows that do not become pregnant are usually culled from the herd. This paper reviews results from studies conducted in South Africa that are aimed at improving the reproductive performance of dairy cows. Records from 9 046 cows in 14 Holstein herds showed that, while lactation number, calving year and calving season affected fertility traits significantly, herd management had the largest effect. Mean ± sd for calving to first service (CFS) and from calving to conception (DO) intervals were 77 ± 30 and 134 ± 74 days, respectively. The number of services per conception (SPC) was 2.55 ± 1.79. The proportion of first services within 80 days post partum and cows confirmed pregnant within 100 and 200 days post partum were 0.64 ± 0.48, 0.36 ± 0.48, and 0.71 ± 0.45, respectively. Heritability (h²) estimates were 0.06, 0.08 and 0.07 for CFS, DO, and SPC, respectively. Albeit low h² estimates were consistent with literature results, the genetic correlation between CFS and DO was positive (0.56), and negative (-0.29) between CFS and pregnancy success. Crossbreeding, using a dual-purpose breed, improved fertility, similar to studies conducted overseas. Increasing the energy content of the total diet of Holstein cows on kikuyu-ryegrass pasture by feeding 7 kg versus 12 kg concentrates/cow/day, improved fertility as a higher proportion of cows were pregnant by 150 days in milk, being 0.52 versus 0.84 and 0.56 versus 0.76 for primi- and multiparous cows, respectively. Estimating breeding values for fertility traits for breeding sires would assist in improving fertility in dairy cows
- ItemFoster parenting, human imprinting and conventional handling affects survival and early weight of ostrich chicks(South African Society for Animal Science, 2012) Wang, M. D.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Bonato, M.; Dzama, K.; Malecki, I. A.The effects of human imprinting and foster parenting by adult ostriches on the survival and growth performance of ostrich chicks were compared to conventional chick-rearing practices in two separate experiments. In the first experiment, the growth rate and survival of chicks imprinted onto humans were compared with those of chicks reared by adult foster parents (n = 100 for both groups). Survival is expressed as proportions, while weights were measured in kg. Treatment did not affect chick survival to 3 weeks (0.90 for imprinted chicks vs. 0.89 for foster chicks), or from 4 to 12 weeks (0.86 vs. 0.83, respectively). Chick weight was not significantly different between groups at 4 weeks, but at older ages, those chicks reared by foster parents consistently outperformed imprinted chicks (means ± SEs being 12.8 ± 0.4 vs. 8.2 ± 0.4 kg at 9 weeks, 37.1 ± 0.8 vs. 19.9 ± 0.80 kg at 18 weeks and 46.2 ± 1.1 vs. 28.6 ± 1.2 kg at 22 weeks). In the second experiment, the treatments consisted of a human-imprinted group of chicks and a group subjected to conventional rearing methods (as customary on the research farm). Chick survival to four weeks was significantly higher for imprinted chicks than for conventionally reared chicks (0.97 vs. 0.84), although chick weight was independent of treatment at 4 weeks (6.27 ± 0.16 kg for the imprinted group vs. 6.18 ± 0.17 kg for the conventional group) and at 15 weeks (respectively 16.5 ± 0.68 vs. 15.2 ± 0.70 kg). Overall, chicks reared by foster parents were heavier than human-imprinted chicks, while early survival of imprinted chicks was better than that of chicks reared by conventional handling. Imprinting thus affected survival of ostrich chicks relative to conventional rearing practices. Because most ostrich chicks are reared with conventional methods, the present study indicates that improvements can be made by adopting alternative approaches. Further studies are needed to ascertain how foster parenting and imprinting may be utilized to optimize chick performance, including the long-term consequences of these practices.
- ItemGenetic analysis of faecal worm egg count in South African Merinos under natural challenge(South African Society for Animal Science, 2007) Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Olivier, J. J.; Du Toit, E.; Dreyer, F. H.Sheep from a Merino selection experiment at the Tygerhoek research farm in the Southern Cape provided material for this study. The selection lines involved included a line selected for clean fleece weight, a "Wet and Dry" line, a fine wool line and an unselected Control line. Rectal faeces samples were obtained from individual animals at 13 to 16 months of age, after drenching was withheld for at least 10 weeks. Nematode eggs in these samples were counted. Fitting the appropriate fixed effects, the heritability of untransformed, cube root transformed and log transformed faecal nematode egg count (FEC) was obtained from single-trait analyses. The effects of sex and birth year were involved in a significant interaction. Means for FEC were generally higher in ram progeny than in ewes, but the magnitude of the sex difference was not consistent. Multiple lambs had a slightly lower mean for FEC than singles, while FEC was unaffected by dam age. The heritability of FEC was estimated at between 0.14 for untransformed data and 0.18 for log transformed FEC. Genetic correlations of log transformed FEC with two-tooth staple strength (-0.49) and coefficient of variation of fibre diameter (0.30) were favourable. Clean fleece weight was unfavourably related to FEC on a genetic level (0.19). Selection for resistance to parasitic nematodes after natural challenge should thus be feasible in the Merino lines studied.
- ItemGenetic and environmental parameters for ewe productivity in Merinos(2002) Duguma G.; Schoeman S.J.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Jordaan G.F.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 which gave birth during the period from 1971 to 1999. Year of birth of ewe and ewe two-tooth liveweight affected the ewe productive traits investigated. Multiple born ewes were superior both in total number of lambs born and weaned compared to 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 lamb weaned per ewe over four lambing opportunities (TWW), respectively. For total weight weaned per ewe over the first lambing opportunity (TWW1) a heritability of 0.02 was estimated. Genetic correlation estimates of -0.10, 0.57 and 1.00 were obtained between TWW1 and TLB, TWW1 and TLW and TWW1 and TWW, respectively. High and positive genetic correlations ranging from 0.61 to 0.92 were estimated between ewe lifetime traits. Genetic progress could be expected when selection is applied on these traits. © South African Society for Animal Science.
- ItemGenetic parameter estimates of early growth traits in the tygerhoek Merino flock(South African Society for Animal Science, 2002) Duguma, G.; Schoeman, S. J.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Jordaan, G. F.Genetic parameters were estimated for birth weight (BWT), weaning weight (WWT) and pre-weaning average daily gain (ADG) using Restricted Maximum Likelihood (REML) procedures. Four different animal models were fitted, differentiated by including or excluding maternal effects. The direct heritability estimates (h2) ranged from 0.19 to 0.38, 0.25 to 0.36 and 0.26 to 0.34 for BWT, WWT and ADG, respectively. The estimates were substantially higher when maternal effects, either genetic or environmental, were ignored from the model. The maternal heritability (m2) for BWT was 0.38 when only maternal genetic effects were fitted in the model but decreased to 0.25 when the maternal permanent environmental effect (c2) was fitted. The m2 for WWT and ADG ranged from 0.05 to 0.11 and from 0.04 to 0.10, respectively. The respective c2 estimates ranged from 0.06 to 0.10 and from 0.06 to 0.09. Moderate negative genetic correlations (ram)between direct and maternal genetic effects were observed in BWT, while close to zero estimates were obtained for WWT and ADG. The direct genetic correlation estimates between BWT and WWT and BWT and ADG were 0.16 and 0.04, respectively. The corresponding maternal genetic correlation estimates were 0.93 and 0.60. The direct and maternal genetic correlation estimates between WWT and ADG were 0.99 and 0.85, respectively. It is suggested that selection should be applied to WWT.
- ItemGenetic parameter estimation of 16-month live weight and objectively measured wool traits in the Tygerhoek Merino flock(2009) Matebesi P.A.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); van Wyk J.B.Genetic evaluation systems require the accurate estimation of genetic parameters. The genetic, phenotypic and environmental parameters for live weight and objectively measured wool traits were estimated for a South African Merino flock. Records of the Tygerhoek Merino resource flock were used to estimate these parameters. The database consisted of records of 4 495 animals, the progeny of 449 sires and 1 831 dams born in the period 1989 to 2004. The pedigree records used have been collected between 1969 and 2004. Direct heritability estimates (h2a) for 16-month live weight (LW) and objectively measured wool traits ranged from 0.20 for staple strength (SS) to 0.68 for fibre diameter (FD). Maternal heritability estimates ranged from 0.05 for LW and FD, to 0.10 for clean fleece weight (CFW). The proportion of the total phenotypic variance due to the maternal permanent environment variance (c2pe) amounted to 5% for fleece weights. The genetic correlation between animal effects for LW, greasy fleece weight (GFW) and CFW were -0.28, -0.65 and -0.70 respectively. The genetic correlation between LW and CFW was positive, but low at 0.14. The other important genetic correlations among the wool traits ranged from low to high, and were variable in sign ((for GFW with CFW (0.87) and with staple length (SL - 0.18); CFW with clean yield (CY - 0.33) and with SL (0.29); FD with CY (-0.09), with SL (0.15), with SS (0.40) and with standard deviation of FD (SDFD - 0.38): CY with SL (0.33) and with SDFD (0.10); SS with coefficient of variation of FD (CVFD - -0.57) and with SDFD (-0.28); CVFD with SDFD (0.87)). These results suggested that worthwhile responses in the objectively measured traits can be achieved through direct and indirect selection. © South African Society for Animal Science.