Graduation - 2024 - December (Open Access)

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Browsing Graduation - 2024 - December (Open Access) by browse.metadata.advisor "Brand, Tertius Swanepoel"

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    Evaluation of the effect of genetic selection on embryonic survival and nutritional supplementation on embryo survival as well as colostrum and milk composition and yield
    (Stellenbosch University, 2024-12) Cilliers, Josephine Elizabeth; Brand, Tertius Swanepoel; van Zyl, Johannes Hendrik Combrink; Cloete, Schalk Willem Petrus; Stellenbosch University. Faculty of Faculty of AgriSciences. Dept. of Animal Science.
    The present study examined genetic selection for or against the number of lambs weaned (NLW) and nutritional supplementation of energy and protein’s impact on embryo and foetal survival. Serum progesterone levels were also measured to determine pregnancy status, embryo losses, and litter size in divergently selected Merino ewes. Additionally, the study investigated the influence of dietary supplementation of the ewe on colostrum and milk quality and yield. The first trial made use of the well-studied Elsenburg Merino resource flock which consists of a high line (HL) and a low line (LL). Embryo survival was monitored through ultrasonograms, but no differences were found between the reproduction lines in terms of conception, lambing rate, or embryo survival. However, ewes from the HL tended to have more lambs per ewe. Serum progesterone levels did not differ significantly between reproduction lines. The rest of the trials were conducted on the Kromme Rhee commercial flock where 240 Dohne Merino ewes were randomly assigned to an experimental diet within a 2x2 factorial design with energy and protein supplementation levels as main effects. Maize (400g/ewe/day vs. 0g/ewe/day) and canola oilcake meal (COCM) (250g/ewe/day vs. 0g/ewe/day) respectively supplied the varying energy and protein treatments to supply high energy (HE) and low energy (LE) diets either with high (HP) or low protein (LP) added to a basic wheat straw diet. Dietary supplementation of energy and protein had no significant effect on embryo losses, though protein supplementation appeared to improve embryo survival in ewes with multiples. The ewes were fed for the total duration of their pregnancy which provided a unique opportunity to conduct colostrum and milk trials on long-term supplemented ewes. Colostrum samples collected post-lambing were analysed for composition, %brix and viscosity. Protein supplementation led to higher fat content, increased somatic cell count, and greater viscosity. This challenges the common belief that energy supplementation is the primary determinant of colostrum quality, highlighting the critical role of dietary protein. For the final trial, milk samples were collected on day 25 after lambing and were subjected to analysis of milk composition. Twenty-four-hour milk production was measured through the use of the weigh-suckle-weigh method and lamb growth was recorded up to weaning. Higher levels of protein supplementation significantly improved the average daily gain (ADG) and weaning weights of lambs. Energy supplementation alone did not enhance milk production. However, it contributed to heavier lambs at weaning. In conclusion, while divergent selection for NLW did not alter embryo losses, dietary supplementation, particularly protein, played a key role in enhancing colostrum quality and milk production. These findings highlight the importance of balanced nutrition for pregnant and lactating ewes. Further research is recommended to aid our understanding of embryo losses and the broader impact of nutrition on sheep reproduction and productivity.