Browsing by Author "Grobler, Barend Jacobus"

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    The influence of superstimulation protocol on oocyte developmental competence in dairy cattle
    (Stellenbosch : Stellenbosch University, 2024-03) Grobler, Barend Jacobus; Lambrechts, Helet; Van Zyl, Johan Hendrik Combrink; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: The increasing demand for dairy products globally, places increasing pressure on dairy producers to select animals for higher milk yield. In South Africa, market forces and the resulting economic pressure have resulted in a decline in the number of dairy producers, which necessitates that existing producers need to increase the average herd size and select dairy animals for a high milk yield, to remain sustainable in the South African dairy sector and to meet the ever-increasing demands of the consumer. The negative impact of selecting dairy animals for high milk yield is reflected in the decline in fertility of dairy animals, not only in South Africa, but globally. The purpose of this study was to evaluate the effects that age, lactation stage, and superstimulation program have on the fertility of Holstein dairy cows. The effect these factors have on fertility was assessed by looking at oocyte developmental competence in an in vitro embryo production system. The selection of the Holstein breed as donor animals, is based on the substantial representation of this dairy breed in the dairy industry. Twelve Holstein cows were selected as oocyte donors and allocated to three different age categories, i.e.3-4 years, 5-8 years, and 10-11 years; and according to stage of lactation, i.e. dry (non-lactating), early lactation (<120 Days in milk) and mid-lactation (>120 Days in milk). The donor animals were then randomly allocated into four different FSH-concentration superstimulation treatment groups (i.e. Control: 0 mg, Low: 150 mg, Medium: 180 mg, High: 240 mg). The superstimulation program and transvaginal oocyte retrieval (TVOR) were repeated every 28 Days, for four repetitions, to ensure that each donor was subjected to each treatment. In this study, the age of the donor and the FSH concentration had no significant effect on follicular wave response, oocyte developmental competence, or embryo yield in an in vitro embryo production system. Lactation stage, although not having a significant effect on follicular wave response, significantly influenced the number of embryos, with non-lactating cows producing 5.63 ± 0.76 embryos, compared to early-lactation cows (2.96 ± 0.53 embryos), and mid-lactation cows (1.97 ± 0.72 embryos). The findings from this study highlighted the impact of dairy cow nutrition on the quality of oocytes, which was more pronounced than the influence of cow age and FSH treatment. The high demand for nutrients in lactating animals disrupts the delicate physiological balance that is required to ensure oocyte developmental competence, in vivo as well as in vitro. The negative impact of lactation on oocyte developmental competence, and the partitioning of nutrients in favour of milk production at the cost of reproduction is clearly highlighted in this study.