SUNScholar - Browsing by Author "Dzama, K."

Browsing by Author "Dzama, K."

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Carcass and meat quality attributes of Malawi Zebu steers fed Vachellia polyacantha leaves or Adansonia digitata seed as alternative protein sources to Glycine max
(South African Society for Animal Science, 2019-05-09) Chingala, G.; Raffrenato, E.; Dzama, K.; Hoffman, L. C.; Mapiye, Cletos
To enhance smallholder beef farmers' capacity to cope with animal feed shortages, especially dietary protein induced by climate change, it is important to evaluate the feeding value of low-cost protein sources naturally available in the environment. The aim of the study was to evaluate carcass and meat quality of Malawi Zebu steers fed diets containing Adansonia digitata (baobab) seed meal or Vachellia polyacantha (white thorn tree) leaf meal as alternative protein sources to Glycine max (soybean) under feedlot conditions. Thirty Malawi Zebu steers (181 ± 21.4 kg body weight; 29 months old) were individually fed forage-based diets made up of rangeland hay and maize bran, with either baobab seed meal, Vachellia leaf meal or soybean meal as a protein source for 120 days. At the end of the feeding trial, animals were slaughtered and the longissimus thoracis et lumborum muscle sampled for meat quality analyses. Steers fed soybean and baobab diets had higher subcutaneous fat thickness, carcass weights than those fed the Vachellia diet. Meat from steers fed the Vachellia and baobab diets had higher ultimate pH and water-holding capacity, and lower drip and cooking losses than meat from steers fed the soybean diet. Feeding baobab and Vachellia diets produced beef with lower lightness (L*) values than the soybean diet, characteristic of dark, firm and dry (DFD) beef. Steers fed the baobab diet had the highest gross profits followed by those fed the Vachellia and soybean diets, respectively. Overall, feeding the baobab and Vachellia diets improved gross profit but produced DFD beef compared to the soybean diet.
The effect of Moringa oleifera leaf meal supplementation on tibia strength, morphology and inorganic content of broiler chickens
(South African Society for Animal Science, 2014-08-13) Nkukwana, T. T.; Muchenje, V.; Masika, P. J.; Hoffman, L. C.; Dzama, K.
This study was conducted to assess the effects of dietary Moringa oleifera leaf meal (MOLM) supplementation as a possible alternative to antibiotic growth promoters on bone breaking strength (BBS), tibia bone morphology and inorganic ash content in broiler chickens. A total of 2400 one-day-old Cobb-500 broiler chicks of mixed sex were randomly allocated to five dietary treatments in six replications of 80 birds per pen. Dietary treatments were as follows: T1, positive control, 668 g salinomycin and 500 g zinc bacitracin per kg of feed; T2, T3 and T4, graded levels of MOLM, that is (starter (1, 3 and 5 g), grower (3, 9 and 15 g) and finisher (5, 15 and 25 g)) per kg of feed; and T5, a negative control (without supplementation). Birds were provided with feed and water ad libitum. Bodyweights (BW) and feed intake (FI) of broilers were measured weekly, and feed conversion ratio (FCR) and average daily gains were calculated accordingly. At 35 days (d) of age, 12 birds per treatment, two from each replicate pen, were randomly selected, stunned electrically at 70 volts, and slaughtered by cervical dislocation. Six left and right tibiae were randomly chosen from each treatment, without being de-fleshed, and were sealed individually in plastic bags to minimize moisture loss. The tibiae were stored at −18 ºC for BBS and tibia ash determination, as well as analyses of their calcium (Ca) and phosphorus (P) composition. Of birds fed diets with higher MOLM levels, T4 had the highest BW, while T1 had the lowest. On days 7 and 21, birds on T4 had the highest average daily gain (ADG) and T1 the lowest, respectively. There were no significant dietary effects in FI on days 7, 21 and 35; while on days 21 and 35, FCR (feed : gain) was highest in MOLM-supplemented birds and lowest in T1 birds, respectively. There were no treatment effects on tibia length (TL), tibia weight (TW) and/or dried tibia weight (DW). A positive correlation (r = 0.667) was observed between TW and DW. There were no treatment effects on BBS and ash percentage, but tibia ash weight was highest in T4 and lowest in T2. Calcium percentage was highest in T1, and lowest in T2 and T5. Phosphorus percentage was lowest in T1 and highest in T5. The highest Ca : P ratio was obtained in T4. The positive correlation observed between BW, TW and TL, and the high P, Ca and ash levels in tibiae from MOLM-supplemented birds depicts the genetic relationship that exists among these parameters. Furthermore, it reveals the effectiveness of MOLM supplementation to enhance nutrient utilization efficiency, increase mineral bioavailability and support bone strength.
Effects of whey, molasses and exogenous enzymes on the ensiling characteristics, nutrient composition and aerobic stability of maize cobs
(South African Society for Animal Science, 2016) Kanengoni, A. T.; Nkosi, B. D.; Chimonyo, M.; Ndimba, B.; Dzama, K.
The study was conducted to assess the effects of whey, molasses and exogenous enzymes on fermentation, aerobic stability and nutrient composition of ensiled maize cobs. Five treatments were ensiled in 1.5 L anaerobic glass jars over 32 days, namely i) control (maize cobs without additives (CON); ii) maize cobs with sugarcane molasses only (MOL); iii) MOL and whey (MOW); iv) MOW and exogenous enzyme at 0.5 g/kg maize cob mixture (ENZ1) and v) MOW and exogenous enzyme at 1 g/kg maize cob mixture (ENZ2). There was a day effect on gross energy (GE) for CON, MOL, ENZ1 and ENZ2 and none for MOW. There was a day effect in ADF for MOL, ENZ1 and ENZ2 and none for CON and MOW. There was lower dry matter (DM) on day 32 compared with day 0 for all treatments. There were treatment effects for GE, crude protein (CP), ash, ether extract, amylase-treated neutral detergent fibre and acid detergent fibre (ADF). On day 32, the neutral detergent fibre (NDF) and ADF concentrations in CON were higher than in MOL, MOW and ENZ2. At day 32, CON silage pH (4.2) was lower than the pH values of ENZ1 (4.5) and ENZ2 (4.6) silages. Acetic acid levels were higher in ENZ1 than ENZ2 silages. Ammonia nitrogen (NH3-N) levels averaged 25 ± 6.6 g NH3-N/kg total nitrogen, which is indicative of satisfactory ensiling. The MOL, ENZ1 and ENZ2 silages produced more carbon dioxide than CON and MOW silages. The addition of molasses and whey did not improve the nutritive quality of the maize cobs after ensiling. Ensiling maize cobs with molasses, whey and exogenous enzymes resulted in lower DM and fibre levels in the maize cobs, which could enhance intake and digestibility of nutrients when offered to pigs as a component of a balanced diet. Further investigations using higher concentrations of whey and molasses are warranted to improve the energy and protein composition of the maize cobs.
Environmental 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.
Estimation of genetic and phenotypic parameters for sow productivity traits in the South African Large White pigs
(South African Society for Animal Science, 2012) Dube, B.; Mulugeta, Sendros D.; Dzama, K.
The objective of the study was to estimate genetic and phenotypic parameters for sow productivity traits of South African Large White pigs, using data from the Integrated Registration and Genetic Information Systems. The analyses were done on 29 719 records for 7 983 sows from 29 herds, which farrowed between 1990 and 2008. Data were analysed as a sow trait using a repeatability animal model. The traits analysed were number of piglets born alive (NBA), litter birth weight (LBWT), 21-day litter size (D21LS) and 21-day litter weight (D21LWT). Estimates of heritability for these traits were 0.07 ± 0.01, 0.11 ± 0.01, 0.03 ± 0.01 and 0.06 ± 0.01, respectively. The respective repeatability estimates for the traits were 0.15 ± 0.01, 0.16 ± 0.01, 0.11 ± 0.01 and 0.12 ± 0.01. Genetic correlations among the traits ranged from 0.32 ± 0.07 between NBA and D21LWT to 0.88 ± 0.04 between NBA and D21LS. The phenotypic correlations ranged from 0.35 ± 0.01 between NBA and D21LWT to 0.75 ± 0.01 between NBA and LBWT. Litter traits at birth were more heritable and repeatable than traits measured at 21 days of age. In general, all traits showed positive genetic and phenotypic trends for the period studied. The heritability of sow productivity traits was low and less repeatable, which suggests that response to selection may be slow and that the performance in the first parity may not always predict future performance. However, because of their economic importance, an attempt should always be made to keep these traits at their optimum.
Factors influencing off-take rates of smallholder sheep farming systems in the Western Cape Provinve of South Africa
(South African Society of Agricultural Extension, 2019) Molotsi, A. H.; Oosting, S.; Cloete, S. W. P.; Dzama, K.
The purpose of this study was to determine off-take rates in smallholder sheep farming systems in the Western Cape province of South Africa. A purposeful sampling technique was used where smallholder farmers were selected based on certain criteria. The criterion set out was that farmers must own between five and 100 sheep. Interviews were conducted with 72 smallholder farmers in three districts, namely the West Coast, Karoo and Eden. General information on the socio-economic status of the farmers was obtained through semi-structured questionnaires. The main sources of income for the Karoo farmers was livestock (46%) and crops for Eden (32%). Farmers in the West Coast area mostly relied on salaries (43%), thus off-farm income. The Karoo district sold a higher average number of lambs per year (41 ± 8.8), with West Coast and Eden selling the same average number of lambs per year at 7 ± 2.2 and 7 ± 2.6 respectively. Overall, the income derived from livestock is low and not economically sustainable. Therefore, different strategies (such as access to market, financial assistance, improved animal nutrition and health management, as well as sound breeding plans) should be employed to assist smallholder livestock farmers to increase off-take rates.
Foster 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.
Genetic analysis of somatic cell score and udder type traits in South African Holstein cows
(South African Society for Animal Science, 2008) Dube, B.; Dzama, K.; Banga, C. B.
Selection accuracy for resistance to mastitis may be increased by combining somatic cell score (SCS) and udder type into an udder health index, using genetic parameter estimates among them. A multi-trait animal model was used to estimate genetic parameters among lactation average SCS and udder type traits in South African Holstein cattle, through REML procedures. Data comprised records on 22 999 Holstein cows in 722 herds, collected through the National Milk Recording Scheme from 1996 to 2002. Average SCS in the first three lactations (SCS1, SCS2, SCS3) were considered as different traits and the udder type traits were fore udder attachment (FUA), rear udder height (RUH), udder cleft (UC), udder depth (UD), fore teat length (FTL) and fore teat placement (FTP). Heritability estimates for SCS were 0.19 ± 0.02, 0.17 ± 0.02 and 0.19 ± 0.02, respectively for SCS 1, SCS2 and SCS3. Udder type traits had heritability estimates ranging from 0.13 ± 0.01 for UC to 0.34 ± 0.01 for FTL. The genetic correlations between lactation SCS ranged from 0.82 ± 0.04 to 0.99 ± 0.03 for correlations of SCS3 with SCS1 and SCS2, respectively. Genetic correlations between SCS and udder type traits were in the range -0.01 ± 0.07 between FUA and SCS3 to -0.38 ± 0.04 between UD and SCS1 and SCS2. Slow genetic progress is expected when selection is applied independently on SCS and udder type traits, due to the generally low heritability estimates. Low, shallow udders with narrowly placed teats are associated with low SCS in the South African Holstein population.
Genetic correlations between female fertility and production traits in South African Holstein cattle
(South African Society for Animal Science, 2007) Makgahlela, M. L.; Banga, C. B.; Norris, D.; Dzama, K.; Ng'ambi, J. W.
Female fertility is increasingly gaining importance in national dairy cattle breeding objectives worldwide. In South Africa, there is no routine prediction of breeding values for reproductive performance in dairy cattle and selection is mainly focused on production traits. The objective of this study was to estimate genetic parameters among female fertility traits (age at first calving and calving interval) and first, second and third lactation production traits in South African Holstein cattle to determine the effect that selection on production per se may have on female fertility. Performance records on 40 437 South African Holstein cows in 766 herds were used. (Co)variance estimates were obtained by multitrait analysis, using the REML procedure. Heritability estimates were moderate for age at first calving (0.24 ± 0.02) and low for calving interval (0.03 ± 0.01). Genetic correlations between age at first calving and yield traits were low to moderately negative, ranging from -0.17 ± 0.07 with second lactation butterfat percentage to -0.50 ± 0.05 with first lactation butterfat yield. Calving interval had moderate to highly positive genetic correlations with yield traits, ranging from 0.37 ± 0.10 with second lactation milk yield to 0.69 ± 0.06 with first lactation milk yield. Correlations between female fertility and butterfat and protein percentages across all lactations, were close to zero. The observed antagonistic relationship between calving interval and production traits highlights the need to include calving interval in breeding objectives for South African Holstein cattle.
Genetic diversity and relationships among indigenous Mozambican cattle breeds
(South African Society for Animal Science, 2009) Bessa, I.; Pinheiro, I.; Matola. M.; Dzama, K.; Rocha, A.; Alexandrino, P.
Three indigenous Mozambican cattle breeds, namely the Angone, Landim and Bovino de Tete were characterized using six proteins, 13 autosomal microsatellite loci and one Y-specific microsatellite locus (INRA124). The Mashona breed from Zimbabwe was also studied to elucidate the origin of the Bovino de Tete cattle. Expected mean heterozygosity ranged from 0.46 - 0.50 in the proteins and from 0.66 - 0.69 in the microsatellites. Population genetic variability was relatively high when compared to other African breeds. Only 4.5% of the total genetic variation could be attributed to the differences among the breeds. DA genetic distances and principal component analysis suggest that Mozambican breeds occupy an intermediate position between Indian Zebu and African taurine cattle. The genetic contribution from Indian Zebu, estimated by mR and average percentage of Zebu diagnostic alleles, was highest in the Angone breed and lowest in the Landim breed. The indicine Y-specific allele was fixed in the Angone breed (classified as Zebu), was found in 62% of the Bovino de Tete breed and was absent in the Landim breed (classified as Sanga). The hybrid nature of these breeds was also revealed by using an admixture model to infer population structure. Cluster analysis correctly assigned individuals to their rightful populations with probabilities ranging from 0.96 to 0.98, using prior population information. The results support the hypothesis of the Bovino de Tete cattle being a result of crossbreeding between Sanga and Zebu breeds. This study presents the first extensive information on the genetic diversity and relationships among Mozambican cattle breeds and with other breeds from different continents.
Genetic prediction models and heritability estimates for functional longevity in dairy cattle
(South African Society for Animal Science, 2015) Imbayarwo-Chikosi, V. E.; Dzama, K.; Halimani, T. E.; Van Wyk, J. B.; Maiwashe, A.; Banga, C. B.
Longevity is a major component of the breeding objective for dairy cattle in many countries because of its high economic value. The trait has been recommended for inclusion in the breeding objective for dairy cattle in South Africa. Linear models, random regression (RR) models, threshold models (TMs) and proportional hazard models (PH) have been used to evaluate longevity. This paper discusses these methodologies and their advantages and disadvantages. Heritability estimates obtained from these models are also reviewed. Linear methodologies can model binary and actual longevity, while RR and TM methodologies model binary survival. PH procedures model the hazard function of a cow at time t derived from survival from first calving to culling, death or censoring. It is difficult to compare methodologies for sire evaluation and ranking across countries because of the variation in the definition of longevity and the choice of model. Sire estimated breeding values (EBVs) are derived differently for the models. Sire EBVs from PH models are expressed as deviations of the culling risk from the mean of the base sires, expected percentage of daughters still alive after a given number of lactations, expected length of productive life in absolute terms or as standard deviation units. In linear, TM and RR modelling, sire EBVs for longevity have been expressed as deviations of survival from the mean estimated with Best Linear Unbiased Prediction (BLUP). Appropriate models should thus be developed to evaluate functional longevity for possible inclusion in the overall breeding objective for South African dairy cattle.
Non-genetic factors affecting fertility traits in South African Holstein cows
(South African Society for Animal Science, 2014-03-08) Muller, C. J. C.; Potgieter, J. P.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Dzama, K.
Profitable milk production and genetic improvement in dairy herds depend largely on fertile cows calving annually to initiate a new lactation period. Over the last 30 years, several studies have indicated a decline in the reproductive performance of dairy cows. From the perspectives of many farmers and veterinarians, the reproductive performance of cows is related to the calving interval (CI) and services per conception (SPC). Using these traits as cow fertility indicators is problematic as CI is dependent on subsequent calving dates, while SPC is strongly linked to inseminator proficiency. Cow fertility refers to the ability of cows to come into oestrus soon after calving, to conceive from a minimum number of services, and to stay pregnant until the next calving. In this paper, non-genetic factors affecting fertility traits other than CI in Holstein cows are discussed. Service records (n = 69 181) and pregnancy check results of 9 046 cows in 14 herds were available. Six fertility traits were derived. Means (± sd) for the interval traits, namely calving to first insemination (CFS) and the interval from calving to conception (days open (DO)) were 77 ± 30 and 134 ± 74 days, respectively, while the number of SPC was 2.55 ± 1.79. The proportion of first services occurring within 80 days post partum (FS80d) and the proportion of cows being confirmed pregnant within 100 days (PD100d) and 200 days post partum (PD200d) were 0.64 ± 0.48, 0.36 ± 0.48 and 0.71 ± 0.45, respectively. While lactation number, calving year and calving season affected reproduction traits significantly, herds (management) had the largest effect.
Non-genetic factors affecting growth performance and carcass characteristics of two South African pig breeds
(South African Society for Animal Science, 2011) Dube, B.; Mulugeta, S. D.; Van Der Westhuizen, R. R.; Dzama, K.
A study was conducted to establish non-genetic factors affecting growth and carcass traits in Large White and Landrace pigs. This study was based on 20 079 and 12 169 growth and 5 406 and 2 533 carcass data collected on performance tested pigs between 1990 and 2008 from Large White and Landrace breeds respectively. The traits analyzed were backfat thickness (BFAT), test period gain (TPG), lifetime gain (LTG), feed conversion ratio (FCR), age at slaughter (AGES), lean percentage (LEAN), drip-free lean percentage (DLEAN), drip loss (DRIP), dressing percentage (DRESS), carcass length (CRLTH) and eye muscle area (AREA). Significant effects were determined using PROC GLM of SAS. Herd of origin, year of testing and their interaction significantly affected all traits. Most traits were not affected by season of testing in both breeds, while all traits in both breeds were significantly affected by sex. Testing environment (station, farm) affected all growth traits except for LTG. Backfat thickness and AGES increased with increasing total feed intake, while other traits decreased as total feed intake increased. Improved test centre management did not compensate for pre-test underperformance. Castrates produced higher carcass yields of lower quality than females, while performance testing showed the best results when done at testing centres. This study showed the importance of adjusting for fixed effects when performing genetic evaluations in the two pig populations.
Potential of using maize cobs in pig diets : a review
(Asian-Australasian Association of Animal Production Societies, 2015) Kanengoni, A. T.; Chimonyo, M.; Ndimba, B. K.; Dzama, K.
The quest to broaden the narrow range of feed ingredients available to pig producers has prompted research on the use of low cost, unconventional feedstuffs, which are typically fibrous and abundant. Maize cobs, a by-product of a major cereal grown worldwide, have potential to be used as a pig feed ingredient. Presently, maize cobs are either dumped or burnt for fuel. The major challenge in using maize cobs in pig diets is their lignocellulosic nature (45% to 55% cellulose, 25% to 35% hemicellulose, and 20% to 30% lignin) which is resistant to pigs’ digestive enzymes. The high fiber in maize cobs (930 g neutral detergent fiber/kg dry matter [DM]; 573 g acid detergent fiber/kg DM) increases rate of passage and sequestration of nutrients in the fiber reducing their digestion. However, grinding, heating and fermentation can modify the structure of the fibrous components in the maize cobs and improve their utilization. Pigs can also extract up to 25% of energy maintenance requirements from fermentation products. In addition, dietary fiber improves pig intestinal health by promoting the growth of lactic acid bacteria, which suppress proliferation of pathogenic bacteria in the intestines. This paper reviews maize cob composition and the effect on digestibility of nutrients, intestinal microflora and growth performance and proposes the use of ensiling using exogenous enzymes to enhance utilization in diets of pigs.
Preliminary genome-wide association study for wet-dry phenotype in smallholder ovine populations in South Africa
(South African Society for Animal Science, 2017-04-10) Molotsi, A. H.; Taylor, J. F.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Muchadeyi, F.; Decker, J. E.; Sandenbergh, L.; Dzama, K.
The aim of this study was to identify single nucleotide polymorphisms (SNPs) associated with genomic region underlying variation in the binomial reproductive trait ‘wet-dry’ in sheep. The wet-dry phenotype was used to represent the reproductive status of the ewes, divided into two categories, dry (ewes that did not lamb or that lost a lamb) and wet (ewes that had lambed and had at least one suckling lamb). Wet-dry records were obtained from smallholder farmers (n = 176) and Nortier Research Farm (n = 131) for the 2014 breeding season. Ages of the ewes ranged from 1 year to 6+ years. Data from 307 individuals were analysed, of which 172 Dorpers and 4 White Dorpers were from smallholder sheep flocks and 48 Dorpers, 46 Namaqua Afrikaners, 26 South African Mutton Merinos, 4 South African Mutton Merino x Dorper and 7 Dorper x South African Mutton Merino crossbreds were from the research farm. A logistic regression model was fitted to adjust the data for the fixed effects of farm, breed, and age of the ewe and weight at mating as a covariate. Linkage disequilibrium (LD) and inbreeding coefficient were estimated using PLINK. Association analysis was performed using the genome-wide efficient mixed-model association package (GEMMA) to determine whether any significant SNPs were associated with the wet-dry reproductive trait. The wet-dry phenotype differed significantly between the smallholder (0.63 ± 0.04) and research farm flocks (0.79 ± 0.04). Genome-wide LD across all populations was r2 = 0.36. Dorpers from the smallholder flock exhibited rapid LD decay versus the resource ovine populations. Inbreeding levels were also lower for the smallholder flock (4 ± 0.003%) versus the research flock (13 ± 0.008%). No significant SNPs were identified after correction for false discovery rate. The heritability estimate for wet-dry using SNP information was 0.24. This estimate concurs with the literature and indicates the possibility of using genomic selection to improve reproduction in smallholder sheep flocks.
Random regression test-day model for the analysis of dairy cattle production data in South Africa : Creating the framework
(South African Society for Animal Science, 2010) Dzomba, E. F.; Nephawe, K. A.; Maiwashe, A. N.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Chimonyo, M.; Banga, C. B.; Muller, C. J. C.; Dzama, K.
Genetic evaluation of dairy cattle using test-day models is now common internationally. In South Africa a fixed regression test-day model is used to generate breeding values for dairy animals on a routine basis. The model is, however, often criticized for erroneously assuming a standard lactation curve for cows in similar contemporary groups and homogeneity of additive genetic variances across lactation and for its inability to account for persistency of lactation. The random regression test-day model has been suggested as a more appropriate method and is currently implemented by several Interbull member-countries. This review traces the development of random regression methods and their adoption in test-day models. Comparisons are drawn with the fixed regression test-day model. The paper discusses reasons for suggesting the adoption of the random regression approach for dairy cattle evaluation in South Africa and identifies the key areas where research efforts should focus. .
Sex of calf and age of dam adjustment factors for birth and weaning weight in Tswana and Composite beef cattle breeds in Botswana
(South African Society for Animal Science, 2009) Raphaka, K.; Dzama, K.
Records on 2 257 Composite and 5 923 Tswana calves born between the period of 1988 and 2006 in Botswana were used to calculate additive correction factors for the effects of sex of calf and age of dam on birth weight and weaning weight. The mature age group in both breeds for the two growth characteristics was 5 - 12 year old dams. Male calves were heavier than their female contemporaries throughout the pre-weaning growth period. The sex of calf adjustments for birth and weaning weights were 2.75 and 8.21 kg in the Tswana while the corresponding values for the Composite were 2.84 and 10.11 kg. Both birth and weaning weights increased with advancing age of dam, reaching a peak in mature dams and declined when dams reached an old age. Age of dam adjustment factors for birth weight in the 3, 4 and 13+ year age groups were, respectively, 1.74, 0.96 and 1.87 kg in the Tswana. Corresponding values for the Composite were 2.28, 0.94 and 2.06 kg, respectively. Age of dam adjustment factors for WW were respectively 10.36 and 5.46 kg for age groups 3 - 4 and 13+ years in the Tswana. Adjustment factors for weaning weight in the Composite breed were 13.84, 3.20 and 9.58 kg for age groups 3, 4 and 13+ years, respectively. These results indicate that adjustment factors for birth and weaning weights should be considered separately for sex of calf and age of dam in these breeds, and also, that these adjustments need to be applied within the breed from which they were derived.
Some insights into the phenotypic and genetic diversity of indigenous pigs in southern Africa
(South African Society for Animal Science, 2012) Halimani, T. E.; Muchadeyi, F. C.; Chimonyo, M.; Dzama, K.
Indigenous pigs in southern Africa are mainly owned by economically vulnerable groups in marginal areas where they are used as a source food, income and security. A study was carried out to achieve three objectives: to describe pig production systems, get a phenotypic description of the pigs and to characterize them genetically. A survey of 199 farmers in three districts in South Africa, (Vhembe, OR Tambo and Alfred Nzo) and one district in Zimbabwe (Chirumhnazu) was carried out. Additional farmers in Malawi (Dedza, Mchinji and Salima) and Zimbabwe (Mutoko) were sampled in order to meet the other two objectives. Most of the pigs (69.7%) were owned by women, with men owning 20.5% and children the remainder. Production of the pigs was constrained by several factors including disease, inadequate feeds, poor housing and lack of knowledge. The majority of the pigs were small and black with characteristics that are probably suited for thermoregulation in arid environments. The third objective was achieved through genotyping 111 pigs using 22 microsatellites. Preliminary results indicate very little differences across populations with an overall inbreeding coefficient of the subpopulation relative to the total population (FST) of 0.071. The results indicate that the indigenous pigs in southern Africa are relatively homogenous.
Towards a regional beef carcass classification system for Southern Africa
(South African Society for Animal Science, 2017-05-15) Chingala, G.; Raffrenato, E.; Dzama, K.; Hoffman, L. C.; Mapiye, Cletos
Southern Africa is home to over 64 million cattle, of which 75% are raised on natural pasture in smallholder farming areas. Indigenous cattle breeds Bos indicus (zebu), B. taurus africanus (Sanga type) and their crosses with B. taurus (European and British) are the most dominant. Despite their dominance, indigenous cattle breeds in smallholder farming areas are commonly marketed through informal markets, and their contribution to formal national economies is therefore limited. This is partly because the current beef carcass grading and classification systems used in the region value inappropriately carcasses from slow-maturing indigenous cattle breeds that are ideally suited to being marketed off natural pasture. The existing systems use carcass yield and quality attributes, but do not predict eating quality at consumer level. Moreover, the principal criteria used to estimate carcass yield and quality, namely age, fat cover and conformation, are assessed indirectly and subjectively. The objective of the current review is to provide an overview of beef carcass grading and classification systems in Southern Africa and analyse their shortcomings in valuing carcasses from indigenous breeds and local production systems. In addition, the review highlights opportunities for improving these systems in Southern Africa and makes suggestions towards developing a regional beef carcass classification system.

Browsing by Author "Dzama, K."

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