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The calpains are involved in the development of meat tenderness by degrading various myofibrillar proteins in skeletal muscles. Members of this proteolytic system include the ubiquitous u-calpain and m-calpain, the skeletal-muscle-specific calpain-3, and calpastatin. Calpastatin is known to inhibit and regulate the activities of the ubiquitous calpains but not calpain-3. Although the postmortem proteolytic role of u-calpain is well established, those of"m-calpain and calpain-3 remain to be clarified. In addition, calpastatin mRNA and proteins exist as three different isoforms in skeletal muscles, but their individual involvement in determining meat quality characteristics in beef cattle has not been ascertained. It is expected that animals and muscle types with higher levels of calpains, and or lower levels of calpastatins would produce meat with improved quality characteristics, i.e. the meat is likely to age faster and become more tender and juicier. This study was therefore carried out to evaluate meat quality characteristics and the expression of the calpain/calpastatin genes in the skeletal muscles of young bulls, steers and heifers. The animals were slaughtered at equivalent live weight of approximately 550 kg, attained at the age of 547, 764 and 889 days for bulls (n = 6), steers (n = 6) and heifers (n = 6), respectively . .Two anatomically distinct muscles, the Longissimus thoracis (LT) and the Semimembranosus (SM), were sampled from each animal to determine their postmortem aging patterns in the different sex groups. Overall, bulls had lower shear force values" than heifers and tended to be lower than steers. Heifer shearforce values tended to be higher than those of steers. A significant (P < 0.001) muscle effect was found, showing higher shear force values for the SM than the LT. In Heifers, the LT did not tenderise effectively and was found to be as tough as the SM. Generally, the LT tenderised early (between 7 to 14 d), while the SM tenderised late postmortem (between 28 to 35 d). Longer aging also reduced the amount of drip from raw meat but had the opposite effect on cooking losses. With the exception of drip loss in bulls which was equal between the two muscles, the LT had a higher water-holding capacity than the SM. Therefore meat quality may be improved by employing a musclespecific aging regime. A trained panel assessed the sensorial qualities of SM steaks subjected to a prolonged aging treatment of 35 d. The panel rated aged meat as more tender (P < 0.01) but could not detect any significant sex differences (P> 0.05).

In this study, a Markov chain model based on the cow’s reproductive cycle, and a financial model were developed to study the variation in profitability in Scottish beef suckler herds resulting from the effect on fertility of disease and/or the employment of alternative management practices. The factors affecting fertility to be economically evaluated were chosen based on the results of the regression analysis combined with the recommendations from the literature. The selected factors were: LBS, feeding management, bull management, the effect of animal disease, i.e. BVDV, and restricted suckling. Feeding management was found to be the most important factor diminishing the financial performance of suckler herds. The total gross margin (GM) was found to diminish by 25% between the optima as a result of the application of a poor and a moderate feeding regimes combined with alternatives lengths of breeding season (LBS) ranging from 42 to 147 days. There were also interactions between the effect of poor bull performance and the LBS so that the effect of poor bull performance is markedly increased by the employment of a short LBS. The losses produced by a BVDV infection varied depending on the proportion of animals of the herd infected by this virus, which varies over time. This aspect was estimated using the model of Gunn et al. (2004), which then provided inputs for the estimation of reproductive performance and gross margins using the models reported here. It was found that BVDV drops profitability of Scottish beef suckler herds by up to 23%. Finally, when restricted suckling was applied for alternative LBS and compared with the economic performance as a result of the application of <i>ad libitum</i> suckling, it was found that profitability was improved by 14% between the two optima.

Thesis (MSc. (Animal breeding and genetics )) --University of Limpopo, 2006 / The objective of this study was to estimate genetic parameters for weekly body weight of feed intake of individually fed beef bulls at centralized testing stations in South Africa using random regression models (RRM). The model for cumulative feed intake included the fixed linear regression on third order orthogonal Legendre polynomials of the actual days on test (7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77 and 84 day) for starting age group and contemporary group effects. Random regressions on third order orthogonal Legendre polynomials were included for the additive genetic effect of the animal and the additional random effect of weaning-herd-year (WHY) and on fourth order for the additional random permanent environmental effect of the animal. The model for body weights included the fixed linear regression on fourth order orthogonal Legendre polynomials of the actual days on test for starting age group and contemporary group effects. Random regressions on fourth order orthogonal Legendre polynomials were included for additive genetic effects and additional uncorrelated random effects of the WHY and the permanent environment. The residual effects for both traits were assumed to be independently distributed with heterogeneous variance for each measurement period. Variance ratios for additive genetic, permanent environment and WHY for cumulative feed intake at different days on test ranged from 0.07 to 0.10, 0.53 to 0.77 and 0.14 to 0.37, respectively. Variance ratios for additive genetic, permanent environment and WHY for weekly body weights at different test days ranged from 0.26 to 0.29, 0.37 to 0.43 and 0.26 to 0.34, respectively. Estimates of genetic correlation among the same trait (body weight or feed intake) measured at different test days were generally high (>0.80) for any give test pair. The WHY had a significant contribution in variation of performance of bulls on test, despite the 28-day adjustment period. RRM provided the opportunity to study changes in genetic variability within the studied traits over time. Random Regression Models could be used in the National Genetic Evaluation of beef bulls at central performance testing stations in South Africa.

The aim of the study was to determine the effects of different dietary fibre levels on methane production and growth performance of Bonsmara and Nguni steers. Nine Bonsmara and nine Nguni male weaners aged 8 – 9 months were used for the study. On arrival, animals were fed Eragrostis curvula hay on ad libitum basis for the first 14 days as part of adaptation to the feedlot environment. Animals were gradually adapted to treatments to prevent metabolic disorders. The study was conducted as a 3 x 3 x 2 factorial experiment. Treatments were allocated in a completely randomised design. Data were submitted to analysis of variance (ANOVA). Student's t-LSD was calculated at the 5 % level (P < 0.05) to compare treatment means for significant effects. Feeding a diet that is low in crude fibre content had significantly increased (P < 0.05) growth performance in both breeds. Bonsmara steers had significantly higher growth performance (P < 0.0001) across all treatment diets compared to Nguni steers. High rumen total microbial count was observed in animals that received diets with low crude fibre. Reducing dietary crude fibre resulted in reduced methane production. Low dietary fibre showed low rumen archaea counts. There was a positive correlation between rumen pH and methane emission for both Bonsmara (R2 = 0.9105) and Nguni (R2 = 0.9517) steers. However, a negative correlation was observed between rumen total microbial count and feed conversion ratio for both Bonsmara (R2 = 0.8286) and Nguni (R2 = 0.7208) steers. The low rumen archaea counts were detected from the Bonsmara. Feeding diets with low fibre levels is recommended for improving growth performance and reducing methane production for Bonsmara and Nguni steers. / Agriculture and  Animal Health / M. Sc. (Agriculture)