Scielo RSS <![CDATA[South African Journal of Animal Science]]> vol. 40 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Ruminal acidosis</b>: <b>a review with detailed reference to the controlling agent <i>Megasphaera elsdenii </i>NCIMB 41125</b>]]> Ruminal acidosis is discussed with reference to causes and economic and health implications. Distinction is made between the acute form which with proper adaptation to high energy diets is seldom encountered and the more problematic chronic or sub-acute form, commonly referred to as sub-acute ruminal acidosis (SARA). Apart from stepwise transition from roughage to concentrates, methods adopted to reduce SARA include grain treatment to reduce starch degradation, feed additives such as buffers to control ruminal pH, dicarboxylic acids to stimulate the growth of lactate utilisers, antibiotics such as virginiamycin and the ionophores which inhibit the growth of lactate producers, and direct-fed microbials (DFM's), some of which are lactate utilisers but used more often as stimulants of the major ruminal lactate utilisers Megasphaera elsdenii and Selenomonas ruminantium. Some of the feed additives are expensive and their effects on SARA mostly inconclusive. With regard to the ruminal lactate utilising bacteria, the potential of M. elsdenii to control lactic acid has been recognized and some success with patented strains has been achieved. However, these strains have not been commercialised because of one or more reasons which include inadequate growth rate, inability to multiply at a low ruminal pH, non-preferential use of lactate as primary substrate, inability to survive in sub-optimal anaerobic conditions, inhibition by ionophores, inadequate delivery methods to the ruminant and inability to keep on producing acetate when fibre digesters become inhibited. Megasphaera elsdenii NCIMB 41125, selected from the concentrate-fed rumen through stringent screening and a pH-auxostat technique, proved to meet most criteria mentioned above. In addition, the strain is unaffected by most anthelmintics and in-feed antibiotics. Research results show that: a) strain 41125 is highly successful in preventing ruminal pH decline and lactic acid accumulation to SARA levels; b) volatile fatty acid (VFA) production is similar to current in-feed products and the proportional contribution depends on substrate, dilution rate and pH. Propionate as preferred VFA can be promoted further by the synergistic benefits of strain 41125 with some antibiotics; c) feed intake may be enhanced but not consistently, apparently depending upon adaptation procedure followed and dietary composition; d) because of effective ruminal acidosis control, less roughage can be used during adaptation which is of economic benefit; e) animal health associated with the SARA-compromised immune system is improved with administration of strain 41125; f) in feedlot cattle carcass gain and carcass feed conversion may benefit by about 2% and in dairy cattle high producers may produce more milk because strain 41125 enables management to challenge these cows with higher levels of concentrate in total mixed rations (TMR's), and g) drenching sheep with strain 41125 before entering harvested maize fields prevents ruminal acidosis. <![CDATA[<b>The effect of a direct fed microbial (<i>Megasphaera elsdenii</i>) on the productivity and health of Holstein cows</b>]]> Sixty high-producing multiparous Holstein cows were used in a randomized complete block design experiment to determine the effect of a direct-fed microbial (DFM), Megasphaera elsdenii NCIMB 41125 (Me), on dairy cattle productivity and health. The cows received one of two experimental diets (total mixed rations (TMR)) from calving until 60 days post partum. Two experimental diets were formulated, namely a low concentrate diet (40% roughage : 60% concentrate) and a high concentrate diet (30% roughage : 70% concentrate) that were fed as a TMR for the duration of the trial. The low and high concentrate diets contained respectively 181 g/kg and 178 g/kg of crude protein, 448 g/kg and 504 g/kg of non-fibre carbohydrate, 282 g/kg and 238 g/kg of neutral detergent fibre and 42 g/kg and 43 g/kg of ether extract. There were four experimental treatments, namely: (1) Low concentrate diet control (LCC), (2) Low concentrate diet and dosed with Me (LCD), (3) High concentrate diet control (HCC) and (4) High concentrate diet and dosed with Me (HCD). Dosing with Me did not show any advantage, regardless of level of concentrate. Dry matter intake, milk production, milk composition, feed efficiency, body mass and body condition score were not affected by treatment. Furthermore, treatment did not affect rumen pH, rumen lactic acid or volatile fatty acid concentrations. Faecal pH, however, was statistically significantly higher, and faecal starch content significantly lower in cows dosed with Me. Lack of results suggests that further research is needed on dose time and/or frequency as well as the option to use it as an infeed product. <![CDATA[<b>Association of polymorphism of the alpha 1-antitrypsin gene with milk production traits in Chinese Holstein</b>]]> Protein degradation in bovine milk affects the quality of dairy products. Alpha 1-antitrypsin (AAT) can protect vulnerable elastic tissues from degradation by neutrophil elastase. The aim of this study was to assess the association of polymorphisms in bovine AAT gene with milk yield and milk composition in Chinese Holstein. Traits analyzed were fat percentage, protein percentage, 305-day milk yield and somatic cell score (SCS). Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), created restriction site-polymerase chain reaction (CRS-PCR) and allele specific-polymerase chain reaction (AS-PCR) methods were used to genotype five loci in coding regions of the sequence, including position 5504, 5609, 5624, 5747 and 8178 in Chinese Holstein. The five mutations were all silent mutation that caused no alteration in the amino acid sequence. In order to determine the relationship between the polymorphisms of the AAT gene and milk production traits and SCS, the General Linear Model (GLM) procedure from the Statistical Analysis Software was used. SNP5504 affected milk fat percentage, SNP8178 affected milk protein percentage and SNP5609 and SNP5624 affected 305-day milk yield. These results suggest that AAT is a candidate gene that influences milk production traits and it could be implemented in breeding programmes to improve the production performance of Chinese Holstein cattle. <![CDATA[<b>Microsatellite-based characterization of southern African domestic pigs (<i>Sus scrofa domestica)</i></b>]]> This paper details genetic characterization and trends from a microsatellite-based study of genetic diversity on southern African pig populations. A total of 351 pigs from three commercial breeds and three indigenous populations were genotyped at 39 loci. Differences among the levels of genetic diversity in populations correlated well with known population histories. In commercial breeds, heterozygosity was higher in the well established SA Landrace and Large White breeds (0.580 and 0.636) compared to the Duroc breed, established more recently (0.531). In indigenous populations, the highest heterozygosity levels were found in the Mozambican and South African populations (0.692 and 0.634) with a lower value of 0.531 in a smaller Namibian population. A hierarchical division of total genetic diversity revealed a high between-population component of 17.9%. F ST- and R ST-based analysis confirmed high levels of differentiation, with pair-wise comparisons between breeds indicating significant differentiation in 20 out of 21 comparisons. Results from an assignment test confirmed results from F ST and R ST and suggested a true genetic structure with significant differentiation between most populations sampled, but with little differentiation among the commercial SA Landrace and Large White breeds. The results are discussed with reference to known historical information on commercial and indigenous pig populations. This paper also presents new data on the optimization of microsatellite markers for application in Sus scrofa domestica. <![CDATA[<b>Effects of dietary replacement of maize grain with popcorn waste products on nutrient digestibility and performance by lambs</b>]]> A study was conducted to evaluate the effects of dietary replacement of maize with popcorn waste (PW) on the intake, nutrient digestibility and growth performance of lambs. Diets replacing 0, 25, 50, 75 and 100% maize with PW were formulated and fed ad libitum to 40 South African Mutton Merino lambs (25.0 ± 0.45 kg live-weight). The diets had similar intake and nutrient digestibility of dry matter (DM), organic matter (OM) and neutral detergent fibre (NDF). Lambs fed the 25 and 50% PW diets had higher intakes of crude protein (CP), metabolizable energy and ether extract compared to the other diets. Growth rate was highest (226 g/d) on the 25% diet and lowest (109 g/d) on the 75% PW diet. Best feed conversion ratio (FCR), of 5.1 (kg feed/kg live weight) was obtained with the 0% PW diet. Improved digestibility of CP and EE occurred in the 25 and 75% PW diets. Higher intake of nitrogen (N) and N retention were obtained in the 25 and 50% PW diets. Dietary replacement of >75% of maize resulted in poor animal performance (ADG < 150 g/d and FCR >7.00). It was concluded that PW can replace up to 50% of the maize in diets for growing lambs. <![CDATA[<b>Genetic parameters for cow weight at calving and at calf weaning in South African Simmental cattle</b>]]> A study was conducted to compare mature cow weight in the South African Simmental population when defined as the weight of the cow at calving or the weight of the cow at weaning of the calf. Data included in the analysis were 14458 records for cow weight at calving (CWT-C) representing 6534 cows and 18871 records for cow weight at weaning (CWT-W) representing 8395 cows. All cows were born between 1968 and 1996, while all calves were born between 1977 and 1998. The following effects had a significant influence on the traits and were included in the genetic analysis: Cow age in years fitted as a covariate term (linear and quadratic) and contemporary group fitted as a fixed effect. Contemporary group was defined as the unique combination of herd, birth year of calf, month of weighing, breeder-defined management group code for the calf and supplementary feeding code for the cow (for CWT-W). All analyses were done using ASREML, first fitting uni-trait and then bi-variate animal models that made provision for up to four weights per cow. The estimated genetic correlation obtained between the two cow weight traits was 0.95 ± 0.03, with a residual correlation of 0.61 ± 0.02. The heritability estimates for CWT-C and CWT-W from this analysis were 0.29 ± 0.04 and 0.37 ± 0.04, respectively. From a breeding perspective, these results confirm that little benefit is to be gained from weighing cows at calving if cows are to be weighed at weaning. If cow weights are to be recorded for an indication of cow maintenance costs, then weight at weaning is the more reliable and practical measure to record. <![CDATA[<b>Effect of dietary olive leaves and rosemary on microbial growth and lipid oxidation of turkey breast during refrigerated storage</b>]]> Forty turkeys were allocated to five groups of eight birds each. One (control) was fed a basal diet while the others were fed diets supplemented with either olive leaves at 10 g/kg, rosemary at 10 g/kg, α-tocopheryl acetate at 150 or at 300 mg/kg feed. Following slaughter, fillets from the breasts of the birds were stored at 4 ºC in the dark for 12 days and their lipid oxidation and microbial growth rate were monitored. Results showed that dietary olive leaves were more effective in inhibiting lipid oxidation of the breast fillets compared to rosemary, but inferior to the dietary supplementation of 300 mg α-tocopheryl acetate/kg. In turn, lipid oxidation was more effectively inhibited when the birds received α-tocopheryl acetate supplementation at 150 mg/kg compared to when the birds received no suppelementation, but inferior to rosemary supplementation. Total viable counts, lactic acid bacteria, Enterobacteriaceae and psychrotrophic bacterial counts were all increased in breast fillets of all groups throughout refrigerated storage. Diet supplementation with a basal level of α-tocopheryl acetate had no effect on the bacterial counts recorded in the control group, but diet supplementation with olive leaves or rosemary resulted in a decrease in all bacterial counts from day 2 of storage and thereafter. During this period olive leaves were more effective in inhibiting bacterial growth than rosemary. <![CDATA[<b>Calving interval genetic parameters and trends for dairy breeds in South Africa</b>]]> Calving interval (CI) is a fertility trait that can be used in selection programmes to minimize the negative effects that selection for production have on fertility. CI can be derived from milk recording data, therefore this fertility trait can easily be implemented in the National Dairy Genetic Evaluations of South Africa. The aim of this study was to estimate genetic parameters for CI for estimation of breeding values and genetic trends to enable South African dairy breeders to assess and select for improved fertility. Breeds included in the study were Ayrshire, Guernsey, Holstein and Jersey. Genetic parameters and trends were based on the first three CIs for all breeds. The genetic software package, VCE4, was used to estimate genetic parameters for CI. Heritabilities ranged from 0.011 for CI1 to 0.069 for CI2, both for the Guernsey breed. Genetic correlations ranged from 0.606 between CI2 and CI3 for the Guernsey breed, to 0.810 between CI1 and CI2 for the Ayrshire breed. Breeding value estimation was done using the genetic software package, PEST. The estimated breeding values were combined into an index value, using weighting factors based on the amount of information available for each trait. Genetic trends were calculated by averaging the CIindices of measured cows per year of birth. These genetic trends indicated that CI increased genetically for all breeds. The genetic parameters will now be implemented for the estimation of CI breeding values, which can be included in selection programmes for improvement of fertility of dairy breeds in South Africa.