Browsing by Author "Van der Merwe, Daniel Andre"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- ItemDeveloping a model for feedlot production of Boer goat slaughter kids(Stellenbosch : Stellenbosch University, 2015-12) Van der Merwe, Daniel Andre; Brand, T. S.; Hoffman, Louwrens C.; Raffrenato, Emiliano; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.ENGLISH ABSTRACT: In this study, the effects of energy content of the feedlot diet as well as the length of the production period were investigated for Boer goat slaughter kids. The kids were housed in individual pens on the Elsenburg experimental farm, Western Cape, South Africa. Boer goat castrate kids were weaned at approximately 18 weeks of age (weighing 22.2 ± 3.5 kg) and were randomly allocated to one of three trial diets that varied in energy content; namely a low, medium and high energy diet (11.3, 12.0 and 12.7 MJ ME/ kg feed respectively) which were supplied ad libitum. The goats were further randomly allocated to one of five slaughter groups that were slaughtered at five week intervals at a commercial abattoir. The first group of goats was slaughtered at the start of the trial in order to serve as a baseline reference. During the study the effects of dietary energy content, and time spent in the feedlot were investigated for the feedlot production and slaughter characteristics of Boer goat kids. Additionally the effect of the energy content of the feedlot diets on the sensory and chemical properties of goat meat were evaluated. During the production period individual feed intake and live weight gain were monitored on a weekly basis. It was observed that live weight of the goats increased throughout the production period. Quadratic functions were used to describe the change in average daily gain and dry matter intake of the goats during the feeding period. Goats that were fed the low and medium energy diets exhibited higher daily gains (P= 0.02) and dry matter intakes (P< 0.01) than goats on the high energy diets. Dietary energy content and age of the animal in the feedlot did not influence the feed conversion ratio to produce a unit of live weight. A linear function was used to model the growth of the goats during this production period. The goats were not able to reach the point of inflection on the growth curve. Therefore the sigmoidal growth curve could not be plotted which could have been modelled by a function similar to the Gompertz model. Dressing percentages of the carcasses varied throughout the production period for all the diets, with goats on the low energy diet having the lowest dressing percentage (45.8%; P= 0.04). The energy content of the trial diets had no effect on the yield of the offal components and retail cuts of the carcass. Generally it was observed that the yields of the hindquarter and neck cuts decreased whilst that of the forequarter increased with the age of the goats at slaughter. The degree of carcass fatness increased with time spent in the feedlot, with the majority of fat being deposited in the abdominal cavity, rather than in the subcutaneous fat depot. Dietary energy content was expected to influence the levels of intramuscular fat, which in turn would affect the eating quality of the meat. However, the levels of energy in the diets fed to goats did not influence the tenderness, juiciness or the aroma and flavour profiles of the goat meat as observed during descriptive sensory analysis of the meat by a trained panel. Chemical analysis of the cooked meat samples also showed that the levels of intramuscular fat did not vary between the samples, resulting in the lack of differences detected between treatments in the sensory evaluation.
- ItemModelling the growth, feed intake and backfat deposition of different South African sheep breed types(Stellenbosch : Stellenbosch University, 2020-03) Van der Merwe, Daniel Andre; Brand, T. S.; Hoffman, Louwrens C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.ENGLISH ABSTRACT: In order to set up a decision support system which can be applied to the feedlot finishing of lambs, models relating to the growth and production of lambs need to be developed. This dissertation presents the details of studies to develop models to describe growth, feed intake, back-fat deposition and wool growth, as well as describe meat, wool and leather quality characteristics of lambs of different breeds. The breeds that were included in the various studies consisted of ewes and rams from Dohne Merino, Dormer, Dorper, Meatmaster, Merino, Namaqua Afrikaner, South African Mutton Merino (SAMM) and White Dorper sheep. In the respective studies, the lambs were reared under optimal growth conditions from birth up until one year of age when they were assumed to have attained a mature body weight. In the growth studies, growth was monitored on a weekly basis from birth, while intake studies commenced when lambs were weaned at ~90 days of age. Measurement of the backfat and longissimus muscle depths was performed using ultrasound scans every two weeks after lambs attained body weights of 20 kg. Wool growth of the lambs was measured using the midrib patch production technique on a monthly basis until lambs were shorn when they attained a mature body weight at one year of age. Appropriate non-linear regressions were fitted to the respective curves of each individual and parameter values were then analysed to test for differences between sexes and breeds. The Logistic, Gompertz and Von Bertalanffy functions were found to appropriately model the sigmoidal growth curves of the various production groups from birth until a mature live weight. On a standard feedlot diet (9.92 MJ ME/kg and 16% crude protein), daily intakes of the different breeds followed a curvilinear trend when plotted against body weight. This trend was modelled using a quadratic function. The peak dry matter intakes estimated from the model for the different breeds were 2203 g/day, 2007 g/day and 1958 g/day for Dormer, Dorper and SAMM breeds, respectively, observed at body weights between 60-70 kg. White Dorper (1879 g/day), Meatmaster (1780 g/day), Dohne Merino (1744 g/day,) and Merino (1560 g/day) lambs obtained peak intakes at ~58 kg body weight. While the quadratic model can be used to observe trends in intake, more accurate linear models can be obtained by modelling the intake expressed as a percentage of body weight against the body weight of the lambs. Similarly, the regressions of cumulative intake with body weight ensured for accurate predictions to be made. The wool producing breeds were assessed to determine wool production rates. Merino sheep were found to have the highest wool growth rates (12.9 g/day) and finest fibre diameter (<20 μm), while Dormer lambs had the lowest wool growth rates (8.5 g/day) and coarsest fibre diameters (>27 μm). Dual-purpose Dohne Merino and SAMM lambs did not differ in terms of wool growth rate (10.1 g/day), though fleeces from Dohne Merino sheep had finer fibre diameters than that of SAMM (21.0 μm and 23.3 μm, respectively; P ≤0.05). Fat deposition, measured using ultrasound scans, could be modelled with body weight (20-65 kg) of the lambs using the exponential function with moderate success. These models showed that early maturing breeds such as the White Dorper and Meatmaster deposit fat at an earlier stage and have greater subcutaneous fat depths at a given body weight than Dorper sheep, which in turn exhibits greater fat deposition than the Dohne Merino, Dormer and SAMM breeds. After modelling the subcutaneous fat depth of the lambs, the ideal slaughter weights of the different breeds could be determined in order to produce a premium lamb carcass in terms of fat cover classification. In a feedlot study where back-fat was monitored, lambs with a back-fat depth of ~4 mm were selected for slaughter and the point of slaughter was taken as the ideal marketing weight. Early maturing Namaqua Afrikaner and Meatmaster sheep had the lowest ideal slaughter weights (32 kg and 35 kg, respectively), followed by Dorper sheep (38 kg) and later maturing Merino, Dohne Merino, Dormer and SAMM breeds (43- 45 kg). Dormer lambs were found to have highest growth rates (438 g/day) and desirable feeding efficiencies (3.71 kg feed/ kg weight gain) in the feedlot; whereas Namaqua Afrikaner lambs exhibited slow growth rates (~169 g/day) with unfavourable feeding efficiencies (~7.08 kg feed/ kg weight gain). The characteristics of the premium lamb carcasses of the various breeds fell within the expectations outlined by the South African carcass classification system, with meat quality traits showing small differences and so indicating a relatively uniform meat product. While the quality characteristics of the different breeds did not vary greatly, the carcasses of fat-tailed breeds differed in composition and conformation to the other breeds, with a majority of the carcass fat being deposited surrounding the tail, with a less developed forequarter region. Sheepskins obtained from the sheep that were slaughtered at the end of growth studies were tanned and the leather characteristics evaluated. Hair type breeds (White Dorper, Meatmaster and Dorper), on average, produced sheepskin leather with a stronger tensile strength (15.23 N/mm2 vs. 9.31 N/mm2; P ≤0.05) and so could be shaved to a thinner, more pliable thickness (1.36 mm vs. 1.78 mm; P ≤0.05) than that of wool type breeds. Skins from hair type breeds also produced a more favourable nappa leather product, while skins from wool type breeds should possibly be used for wool-on leather products. The models and results obtained in the above studies can be used to run simulations of feedlot rearing situations of different sheep breeds and predict the possible outcomes. Ideal slaughter weights for the lambs, in terms of market specifications, or optimal profitability can then be determined to assist the producers in decision making. The results also indicate the product quality of meat, wool and leather from the different breeds, which can assist the producer as well as processor in deciding on the most appropriate marketing strategy for optimal profitability.