Masters Degrees (Animal Sciences)

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Browsing Masters Degrees (Animal Sciences) by browse.metadata.advisor "Cloete, J. J. E."

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    The effect of slaughter age on the lamb characteristics of Merino, South African Mutton Merino and Dorper lambs
    (Stellenbosch : University of Stellenbosch, 2010-03) Van der Westhuizen, E. J.; Brand, T. S.; Hoffman, Louwrens C.; Cloete, J. J. E.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: The aim of this study was to investigate the effect of feedlot production on the growth and carcass characteristics, as well as the distribution of the main tissues (muscle, fat and bone) and meat quality of Merino, South African Mutton Merino (SAMM) and Dorper lambs. The Merino and SAMM 2008 outperformed (P<0.05) the 2007 SAMM and both Dorper production groups in terms of average daily gain, while the Merino and both SAMM production groups achieved the best feed conversion ratio (P<0.05). The highest percentage A2 graded carcasses was achieved after 42 days under feedlot conditions by the Merino and both Dorper production groups, but it took only 21 days in the feedlot for the SAMM lambs to achieve the same result. Slaughter weight, carcass weight and dressing percentage all increased significantly with an increase in the number of days under feedlot conditions for all three breeds, while a decrease in the percentage head, trotters and red offal was also documented. The fatter retail cuts (thick rib, flank, prime rib and loin) increased (P<0.05) in percentage with an increase in the number of days under feedlot conditions. A significant decrease in the percentage leaner retail cuts (raised shoulder and hind-quarters) was found when the amount of days under feedlot conditions increased. The highest profit is obtained by the prime rib, loin and hind-quarters in a lamb carcass. For the Merino and Dorper lambs these three cuts, or a combination of the three showed the highest combined percentages after 42 and 63 days under feedlot conditions, respectively. The late maturing SAMM lambs achieved the highest percentages for these three cuts after 63 and 84 days under feedlot conditions in 2007 and 2008 respectively. Visceral and renal fat deposition increased throughout the production period for all breeds. The Dorper lambs attained the highest subcutaneous fat depth, and also produced the heaviest, but fattest carcasses. For A2-graded carcasses, Dorper lambs had the highest dressing percentage and lowest subcutaneous fat depth, followed by the SAMM and then Merino breed. A decrease in the percentage muscle and bone was found with an increase in the number of days under feedlot conditions, whilst an increase in the percentage fat was found under the same conditions. Meat quality was mostly affected by the 48h post mortem pH. This pH value is affected by the cooling rate of the carcasses, which in turn is affected by the level of carcass fatness. Carcass fatness increased with an increase in the number of days under feedlot conditions, resulting in a low 48h post mortem pH. A low 48h post mortem pH is accompanied by higher percentages of cooking and drip loss, as well as a high a*-colour reading for all three breeds.
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    Ruminal and intestinal digestibility of rumen protected lysine and its effect on production responses in Merino rams
    (Stellenbosch : Stellenbosch University, 2020-04) Uys, Janien; Van Zyl, Johan Hendrik Combrink ; Cruywagen, C. W.; Cloete, J. J. E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: Wool is a large export commodity in South Africa where the price is determined by supply and demand. The average clean wool price per kilogram for the 2017/2018 wool clip season was R183.84 (top lines). This represents a price increase of approximately R30.00/kg (16.3%) in just one clip season. Therefore, improving the production of wool or optimizing the cost of the production of wool is of importance to the economic contribution of this farming sector. A major objective in any animal production system is to increase the efficiency of converting nutrients into animal products. Some research suggested that the fibre growth of sheep may be limited by protein content that could be inadequate in the diet. These studies also reported that additional protein supplementation can influence wool yield. However, it was also reported that dietary protein supplementation had a negative influence by increasing fibre diameter. Another study reported that when ruminal degradation of high quality protein is reduced, substantial increases in the growth rate of wool is possible. Microbial protein (MP) alone is likely to meet the maintenance requirements of an animal but it is often insufficient to meet the demand for optimal production. Currently, various attempts have been made to develop and produce amino acids (AA) that escape degradation in the rumen. Due of the large quantities of AA that are degraded in the rumen, there is a lack of information on the availability of AA in the lower digestive tract of ruminants. This has prompted researchers to develop concepts to protect proteins from ruminal degradation, increase the supply of proteins for production and reduce nitrogen losses as urea via urine. Such methods include structural manipulation to produce AA analogues and AA coated with resistant materials. The capsule can thus resist degradation of AA in the neutral pH-environment of the rumen, but the AA would be made available for enzymatic digestion at the lower pH of the small intestine. Little research has been done, not only on the use of synthetic AA in ruminants, but more so on wool producing sheep. The purpose of the current study was thus to determine whether or not rumen-protected lysine could improve the wool production of Merino sheep. More so wool growth, thus fibre length, fibre diameter, staple strength, fibre curvature and clean fleece weight, by supplementing the diet with high or low levels of bypass lysine or rumen degradable lysine. The objectives of the study were to investigate the effect of different levels and type of dietary lysine on the production parameters of Merino rams. A secondary objective was thus to determine the difference in rumen degradability and intestinal digestion of rumen degradable lysine and bypass lysine. The final objective was to determine the absorption of this dietary lysine in the lower digestive tract when considering different inclusion levels of degradable and bypass lysine. In the first trial, 40 Merino rams were supplemented with a diet that contained either high or low levels of bypass lysine and rumen degraded lysine. Merino rams with an average weight of 37kg and 1.5 years old, were fed for three months and during this period the feed intake were recorded daily to calculate the average daily intake (ADI) and the sheep were weighed weekly to calculate average daily gain (ADG). Blood samples were taken at the beginning of the trial and once during the trial to determine lysine absorption into the blood plasma. At the end of the trial, all the rams were sheared to determine wool production parameters throughout the trial. This study showed that supplementation of the bypass AA significantly (P ≤ 0.05) increased the dry matter intake (DMI) of the rams. None of the measured wool parameters showed any differences between treatments. The blood plasma lysine levels were only significantly higher (P ≤ 0.05) for the diets high in lysine but were not affected by degradability type. It was concluded that the use of rumen protected lysine as a supplementation in Merino rams showed little response to production parameters. The second part of this study was to determine the apparent ruminal and intestinal digestibility values of a commercial lysine product by means of a three-step in vitro procedure, commonly referred to as the Ross Assay. The trial was done as a randomized block design with two types of commercial lysine products (rumen degradable and rumen protected) and six replications, where three cows were used as rumen fluid donors in two separate runs. The modified Ross Assay used in the trial was divided into two phases. This first phase represented the ruminal degradation phase and the second phase represented intestinal digestion. No significant differences in ruminal degradation or intestinal digestibility were observed between the two products. It was thus concluded that the encapsulation of the bypass lysine product did not decrease in vitro rumen degradation and neither did it increase the availability of lysine for absorption in the lower digestive tract.
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    Studies on the genetics of ovine behaviour in a Western Cape resource flock aimed at improving animal welfare
    (Stellenbosch : Stellenbosch University, 2019-04) Burger, Marelee; Cloete, Schalk W. P.; Dzama, Kennedy; Cloete, J. J. E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Data were collected on a Merino resource flock on the behaviour of ewes and lambs from 1993 to 2002. This flock was divergently selected from the same base population since 1986 for the number of lambs weaned per mating (NLW). Selection resulted in two selection lines, namely the High line (H line, upward selection for NLW) and the Low line (L line, downward selection for NLW). Additionally, the effect of these behaviours and selection lines were reported for NLW and lamb survival, as a key welfare indicator trait. Data from arena behaviour on Merino weaners were also collected over a 15-year period using the same resource population divergently selected for NLW. Ram lambs, progeny of mature ewes and singles were heavier at birth than ewe lambs, progeny of young and old ewes and multiples respectively. H line lambs had shorter lengths of parturition than L line lambs, where this difference was also found in H line and L line ewes. The effects of dam age were significant for the latency from birth to suckling as it improved with ewe age, and in both ewe and lamb studies H line ewes had better maternal cooperation scores than L line ewes. Maternal cooperation also had a significant effect on the latency for the lamb to progress from birth to suckling and maternal cooperation score improved with age in ewes. H line ewes had an improved NLW compared to L line ewes while H line lambs had a better survival. For production traits, H line lambs derived from embryo transplants were heavier at yearling age, had a lower fibre diameter, less wrinkles at the neck, body, breech and overall when compared to L line lambs. Survival of lambs reared by surrogate dams was higher in the H line than in the L line. Single-trait direct heritability estimates (h²) in lambs were 0.15 for birth weight, 0.07 for lamb survival, 0.06 for length of parturition, 0.12 for latency from birth to suckling and 0.00 for maternal cooperation score. Direct heritability estimates, assessed as trait of the ewe, were 0.04 for NLW, 0.17 for length of parturition, 0.07 for maternal cooperation score and 0.20 for the interval ewes remained on or near their lambing sites. Genetic trends suggested divergence between the lines for breeding values for length of parturition, suggesting that parturitions became shorter in the H line and longer in the L line. The results and parameter estimates obtained, suggested that selection for improved NLW would yield desirable outcomes for ewe behavioural traits. Maternal permanent environment variance ratios (c²) were 0.07 for lamb survival and 0.17 for maternal cooperation score. Survival of the lamb was favourably correlated to the length of parturition and maternal behaviour score on the genetic level. It was evident that neonatal behaviour was, to an extent, under genetic control in paddock-reared sheep. In the arena test, animals from the H line approached closer to stationary human seated between the test animal and its flock mates and had fewer urination and defecation events than their L line contemporaries but travelled longer distances in the arena. The distance the lambs maintained from the human operator (0.08), urinating events (0.13), and defecating events (0.04) were all lowly heritable. However, the number of lines crossed (0.22) and the number of bleats (0.35) were moderately to highly heritable. Selection for NLW and certain neonatal and perinatal ewe behaviours would benefit the welfare of ewes and lambs. From the arena test it was also evident as H line lambs experienced lower levels of stress in the contrived area environment.