Scielo RSS <![CDATA[South African Journal of Animal Science]]> vol. 43 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>A review of genomic selection - Implications for the South African beef and dairy cattle industries</b>]]> The major advancements in molecular technology over the past decades led to the discovery of DNA-markers, sequencing and genome mapping of farm animal species. New avenues were created for identifying major genes, genetic defects, quantitative trait loci (QTL) and ultimately applying genomic selection (GS) in livestock. The identification of specific regions of interest that affect quantitative traits aimed to incorporate markers linked to QTL into breeding programs by using marker assisted selection (MAS). Most QTL explained only a small proportion of the genetic variation for a trait with limited impact on genetic improvement. Single nucleotide polymorphism (SNP) markers created the possibility to genotype cattle in a single assay with hundreds of thousands of SNPs, providing sufficient genomic information to incorporate into breeding value estimation. Genomic selection is based on the principle of associating many genetic markers with phenotypic performance. A large database of genotyped animals with relevant phenotypes pertinent to a production system is therefore required. South Africa has a long history of animal recording for dairy and beef cattle. The challenge for implementation of GS would be the establishment of breed-specific training populations. Training populations should be genotyped using a high density SNP panel, and the most appropriate genomic prediction algorithm determined. The suitability of commercially available genotyping platforms to South African populations should be established. The aim of this review is to provide an overview of the developments that occurred over the past two decades to lay the foundation for genomic selection with special reference to application in the South African beef and dairy cattle industry. <![CDATA[<b>Estimates of variance components for postweaning feed intake and growth in Bonsmara bulls and evaluation of alternative measures of feed efficiency</b>]]> Feed efficiency is of major economic importance in beef production. The objective of this work was to evaluate alternative measures of feed efficiency for use in genetic evaluation. To meet this objective, genetic parameters were estimated for the components of efficiency. These parameters were then used in multiple-trait animal model genetic evaluations and alternative genetic predictors of feed efficiency were derived from the results. Corresponding single-trait evaluations for residual feed intake (RFI), residual daily gain (RDG), and residual intake and gain (RIG) were also conducted. The data contained 3 331 animals with records and an additional 6 322 animals in their pedigree. The alternative measures of feed efficiency were compared using Spearman rank correlations. Heritability estimates for metabolic body weight (MBW), average daily gain (ADG) and average daily feed intake (DFI) were 0.38 ± 0.05, 0.25 ± 0.05 and 0.37 ± 0.05, respectively. Estimates of the genetic correlations among these traits were 0.79 ± 0.07, 0.54 ± 0.08 and 0.66 ± 0.08 for MBW with ADG, MBW with DFI, and ADG with DFI, respectively. The various measures of feed efficiency were highly correlated. However, RFI and RDG did provide different rankings of candidates for selection. The combination of RFI and RDG to form RIG appears to provide an effective harmonization of the former two biological measures of efficiency. It is recommended that genetic evaluation systems include analyses of ADG and DFI, and breeders are advised to base selection decisions on the basis of multiple-trait selection indexes that incorporate feed intake and performance. <![CDATA[<b>Effect of dietary protein on performance of four broiler strains and on the allometric relationships between carcass portions and body protein</b>]]> This is the second paper in a series that reports the allometric relationships between some of the physical parts and body protein weight of commercial broiler strains reared, sexes separate, on different dietary protein levels. In this trial, four commercial broiler strains were sampled at day old and then weekly from each of three dietary protein treatments to determine the weights of the physical parts and the chemical composition of each of 936 birds. Allometric regressions were compared between strains, sexes and dietary protein levels using linear regression with groups. Whereas these regressions were similar over strains and sexes, some interactions were evident between factors, the largest differences occurring when broilers were fed differing dietary protein levels. These differences may be explained on the basis that lipid is deposited to different extents in each of the parts in response to dietary protein. Day-old breast meat and wing weights fell below the regression that best fitted the remaining observations and so were omitted from allometric analyses. The allometric regressions presented are an attempt to provide information that would enable the prediction of the weights of breast meat, thigh, drum and wing at different stages of growth of broilers whose genotype and feed composition are adequately described. <![CDATA[<b>High levels of maize in broiler diets with or without microbial enzyme supplementation</b>]]> A total of 210 day-old male Cobb broiler chickens were randomly assigned to six treatments in a 3 x 2 factorial design. The treatments consisted of three levels of maize: 250 g/kg (LM), 500 g/kg (MM) and 750 g/kg diet (HM) and two levels of enzymes: plus enzyme and no enzyme. Each treatment was replicated five times, with seven birds per replicate. Chickens were reared in multi-tiered brooder cages to 21 days of age in a climate-controlled room. Feed and water were provided ad libitum. Over the feeding period (21 d), there was an increase in feed intake as maize inclusion level (MIL) increased in diets, while supplementation with microbial enzyme improved feed intake only in the MM diet. There was an improvement in live weight (LW) in chickens with increased MIL in their diets. The microbial enzyme supplement also improved LW, but only on the MM diet. The feed conversion ratio (FCR) was improved with increase in MIL in diets, but the enzyme supplements had no effect on FCR up to day 21. At day 21 there was an increase in relative weight of the small intestine with an increase in MIL, but this was not affected by enzyme supplementation. The weight of the liver increased with increase in MIL and enzyme supplementation. At day 21 the pH of the digesta in the gizzard declined with an increase in MIL in diets. In general, there was no significant effect of MIL or enzyme supplementation on pancreatic tissue protein content, chymotrypsin amidase activity and ileal digestibility of protein, gross energy and starch at 21 days of age. The population of Clostridium perfringens decreased significantly with increase in MIL, but other microbial species were unaffected. The present findings suggest that maize could be included at much higher levels than is currently done without detrimental effects on productivity. Exogenous enzymes also resulted in a significant increase in some of these variables. <![CDATA[<b>Effects of ultrasonic waves on eggshell strength and hatchability of layer-type breeder eggs</b>]]> Two trials were conducted to investigate the effects of exposing layer-type breeder eggs before incubation to ultrasonic waves (ULT). Eggs were subjected to ULT of 117 volts at 40 kHz for up to 15 minutes. Eggshell breaking force (EBF), hatchability and chick hatching weight (CHW) of Balady breeder eggs (Trial 1), and egg weight loss, embryo weight, hatchability and CHW of Leghorn hen eggs (Trial 2) were measured. In Trial 1 the eggs were subjected to seven treatments: non-dipped (control), and dipped for 5, 10 and 15 minutes in a water bath (W5, W10 and W15) or a ULT bath (ULT5, ULT10 and ULT15). In Trial 2 the eggs were subjected to four treatments, a control (ULT0) and the ultrasonic treatments, ULT5, ULT10 and ULT15. In treatments ULT10 and ULT15 the EBF of Balady eggs was significantly reduced while the hatchability of the Balady and Leghorn eggs was significantly reduced by the ULT15 and W15 treatments, compared with the control. Orthogonal contrast (control vs. ULT) indicated that ULT exposure of eggs reduced their EBF significantly. Percentage egg weight loss, embryo weight and CHW was not affected by the treatments. It was concluded that exposure of eggs to ULT of 117 volts at 40 kHz for 15 minutes reduced EBF and hatchability of layer-type breeder eggs without altering egg weight loss, embryo weight or CHW. <![CDATA[<b>Oestrus induction using fluorogestone acetate sponges and equine chorionic gonadotrophin in Red Sokoto goats</b>]]> The objective of this study was to evaluate the effect of a progestagen treatment (fluorogestone acetate sponge) alone or in combination with equine chorionic gonadotrophin (eCG) on oestrus response in Red Sokoto (RS) goats. One hundred RS does were treated with 30 mg fluorogestone acetate (FGA) sponges for 14 days. At the end of the progestagen treatment, does that retained the sponges were allocated to two groups; FGAeCG and FGA. The FGAeCG group (n = 28) received 200 IU eCG i.m. concurrently with the sponge removal, while the FGA group (n = 28) did not receive eCG at sponge removal. Oestrus was detected twice daily (at 07:00 - 10:00 and 15:00 - 18:00) using sexually active bucks for five days following progestagen withdrawal. There was no significant difference in oestrus response between groups FGAeCG (82.1%) and FGA (78.6%). There was a significant difference in the time to the onset (29.3 ± 4.6 and 44.2 ± 6.3 h for the FGAeCG and FGA, respectively) and duration of the induced oestrus period (38.9 ± 5.1 and 22.7 ± 4.6 h for the FGAeCG and FGA groups, respectively). It is concluded that although both groups showed good oestrus synchronization rates, administration of eCG shortened the time to onset of oestrus and increased the duration of oestrus in Red Sokoto does. <![CDATA[<b>Beef cattle welfare evaluation during the dry season in the northern Mexico's cow-calf system using a visual methodology</b>]]> A cattle welfare index was estimated through 14 visual indicators in the cow-calf system in northern Mexico. The study was carried out at 25 ranches in Chihuahua, Mexico. The indicators were rangeland forage availability; rangeland plant diversity; ease of walking owing to terrain slope; ease of walking owing to presence of rocks; water availability; water distribution; water distance; water appearance; heat protection through vegetation; cold protection through vegetation; cold protection through topography; cold protection through management; cattle docility and cattle body condition. A score of 1 to 4 was given to each indicator, rated as poor, fair, good and excellent, respectively. Ranches under study were classified according to their dominant vegetation type. Noticeable differences were obtained among animal welfare indexes, depending on rangeland type. The lowest index of 2.82 was recorded for the desert shrublands, while indexes above 3.0 were observed for the shortgrass prairie and oak-bunchgrass rangelands. Indicators with high values were water availability and distribution. The lower cattle welfare scores were related to natural factors rather than to management indicators. <![CDATA[<b><i>In vitro</i></b><b> fermentation of diets incorporating carob pulp using inoculum from rabbit caecum</b>]]> The aim of this work was to evaluate the nutritive value of carob pulp for rabbits using the in vitro digestibility and gas production techniques with inocula from caecal content of rabbits. Experimental diets contained 0% (D1), 10% (D2), 20% (D3) and 100% (D4) carob pulp on a dry matter (DM) basis and were incubated in glass syringes for 72 h at 39 °C. Carob pulp contained 313 g neutral detergent fibre/kg DM with a high acid detergent fibre (263 g/kg DM) content, resulting in a low hemicellulose content of 50 g/kg DM. Potential gas production ranged from 123 (D1) to 179 (D4) mL/g DM and was similar for the D1 (123 mL/g DM), D2 (126 mL/g DM) and D3 (130 mL/g DM) treatments. The lowest pH value of 6.47 and the highest organic matter degradation (OMD, 64.3%) were observed in the 100% carob pulp (D4) treatment, while its inclusion at 10% and 20% tended to improve the OMD of the diets. These results show that carob pulp is well fermented by the caecal micro-organisms of rabbits. Although its inclusion at 20% did not improve in vitro fermentation and degradation of the commercial concentrate, it was concluded that carob pulp has potential as an unconventional feed resource for rabbits. Its utilization could have a positive effect on intestinal microbiota owing to its high content of soluble fibre. <![CDATA[<b>Comparison of proximate and fatty acid compositions of wild brown trout and farmed rainbow trout</b>]]> The purpose of this study was to compare the fatty acid and proximate composition of two commercially exploited trout species (wild brown trout (WBT) and farmed rainbow trout (FRT)). The mean crude lipid content in FRT (4.3%) was significantly higher than that in WBT (2.7%). Total saturated fatty acid concentration (27.7%) in WBT was significantly higher than that in FRT (21.4%). However, monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) concentrations in FRT were significantly greater than those of WBT. While the omega-6 PUFA concentration of WBT was fairly low, total omega-3 PUFA concentration was significantly higher compared with omega-6 PUFA. In contrast to WBT, the FRT contained high omega-6 and low omega-3 PUFA concentrations. Linolenic, docosahexaenoic (DHA), eicosapentaenoic (EPA) acids and C20:3n-3 components of omega-3 PUFAs were higher and significantly different between the two species. The ratio of omega-3 to omega-6 fatty acids in WBT was significantly higher compared to FRT. The results indicated that muscle lipids of both species are rich in EPA + DHA, thus beneficial in human nutrition. <![CDATA[<b>Changes in the air cell volume of artificially incubated ostrich eggs</b>]]> A total of 2160 images of candled, incubated ostrich eggs were digitized to determine the percentage of egg volume occupied by the air cell at different stages of incubation. The air cell on average occupied 2.5% of the volume of fresh eggs. For eggs that hatched successfully, this volume increased to an average of 24.4% at 41 days of incubation, just prior to hatching. Air cell volume at 29 days of incubation for infertile eggs (19.3%) was significantly higher when compared to dead-in-shell (DIS) eggs (14.3%) and eggs that hatched (13.8%). There was a significantly larger air cell volume in eggs that hatched normally compared with DIS eggs at 41 days of incubation (28.3% vs. 21.7%, respectively). No differences in air cell volume were observed up to day 17 of incubation for eggs that hatched normally between eggs that exhibited high, average or low rates of water loss, but from 20 days of incubation the air cell volume was significantly larger for high weight loss eggs. However, for the DIS eggs, air cell volume was consistently larger in eggs that exhibited high rates of water loss. Air cell volume was largely independent of adult strain (SA Black or Zimbabwean Blue) or whether chicks were assisted to hatch. Although some subtle differences in air cell size were detected between hatched and DIS chicks during this study, it is unlikely to find useful application in the broader industry. <![CDATA[<b>A survey on the effect of transport method on bruises, pH and colour of meat from cattle slaughtered at a South African commercial abattoir</b>]]> In this study the effect of transport method on bruising, ultimate pH (pHu) and colour of beef (L* = lightness, a* = redness and b* = yellowness) was determined. Cattle transported directly from farms had the highest bruise scores, pHu and the lowest L* values. There were significant correlations between pHu and L*, a* and b* values, (r = -0.45, r = -0.59 and -0.55, respectively), pHu and bruise score (r = 0.34), and L* and bruise score (r = -0.24). There were positive relationships between transport distance and pHu and between distance and bruise score, while the relationship between L* and distance was negative. Percentage of bruised carcasses varied with method of transport: Group 1, 41.1%; Group 2, 63.1% and Group 3, 51.1%. Transport method affected bruising, pHu and colour of beef. <![CDATA[<b>Analysis of inbreeding of the South African Dairy Swiss breed</b>]]> In South Africa, the Dairy Swiss breed, which originated in Switzerland, consists of 27 breeders and 1135 breeding cows. Pedigree information on the breed was analysed to determine its effective population size (Ne) and rate of inbreeding. The rate of inbreeding was 0.08% per year and 0.38% per generation. It was estimated that in 2008, over 90% of the animals were inbred. This is within the acceptable recommendation for an effective population size of 50 - 100, with an Ne value of 89. However, the high percentage of inbred animals may start to have a detrimental impact on the effective population size and breeders need to exercise caution in their breeding decisions. <![CDATA[<b>Evaluation of the BovineSNP50 genotyping array in four South African cattle populations</b>]]> The BovineSNP50 genotyping array is a product with a wide range of applications in cattle such as genome-wide association studies, identification of copy number variation and investigation of genetic relationships among cattle breeds. It also holds potential for genomic selection, especially for traits that are expensive and difficult to measure. The successfulness of this chip for any of these applications depends on the degree of polymorphisms in the cattle breeds. The SNP50 array has not been validated in any South African cattle population and this could lead to overestimating the number of polymorphic SNPs available for application in it. This study is a first attempt to evaluate the Bovine64SNP50 genotyping array in the South African cattle population. Ninety six bovine samples, consisting of 45 Holstein, 29 Nguni, 12 Angus and 10 Nguni x Angus crossbred animals, were genotyped with the BovineSNP50 infinium assay. The results of this study demonstrated that 40 555 SNPs were polymorphic (MAF >0.05) in these breeds and indicate potential for application in South African cattle populations. Genomic information generated from the BovineSNP50 can now be applied in genetic prediction, genetic characterization and genome-wide association studies.