Browsing by Author "Stapelberg, Wian"

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    The influence of heat stress on the functionality of ovine spermatozoa
    (Stellenbosch : Stellenbosch University, 2022-04) Stapelberg, Wian; Lambrechts, Helet; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: With the current trend in the global human population growth, the demand for animal production is predicted to increase significantly in the coming years. The increased demand for animal products will coincide with the period in which the world will experience changes in the global climate that will ultimately affect agricultural production. When considering the use of assisted reproductive techniques in the sheep industry, given the expected increase in average global temperatures, it is important to identify rams that produce spermatozoa that are resilient to temperature changes associated with the collection, processing, and preservation. This study aimed to determine the influence of scrotal insulation on sperm sample quality, and the resumption of normal spermatogenic activity in the testes of adult Dohne Merino rams, to potentially classify rams in terms of resilience to heat stress and its related effect on physiological processes such as spermatogenesis. Twelve rams formed part of the scrotal insulation phase, of which 10 rams were subjected to scrotal insulation. Two rams were not subjected to scrotal insulation and represented a Control group. The scrotal insulation devices were fitted after the first semen sampling, and thermographic measurements (Week 0), and remained fitted for 7 consecutive days. Semen samples and thermographic measurements were recorded after removal of the scrotal insulation devices, and thereafter every fortnight at Week 3, 5, 7, 9 and 11. The fitting of scrotal insulation devices in the present study proved to be effective in insulating the testes, as evident in the influence thereof on spermatogenic activity. There were no significant differences between the HR, LR, and Control groups for the percentage of abnormal and live spermatozoa over time during liquid storage (0-48h). There was a difference in the ability of spermatozoa from the rams to offer resilience to heat stress when the entire sampling period of 11 weeks was considered. Sperm morphology took 70 days to achieve pre-insulation values (below 40% for most rams), indicating that early spermatogenesis was most affected by heat stress. Considering the change in ambient temperature at Week 0 and Week 11 of the study as well as the different times of measuring scrotal temperatures during those weeks, scrotal temperatures took approximately 42 days to recover (18.64 ̊C – 24.84 ̊C), which coincides with the time it takes for spermatozoa to be produced from spermatogonia. By assessment of the change in iButton and scrotal temperatures, it was found that there were individual differences between rams, which indicates that certain rams are more efficient in thermoregulating testicular temperature than others. The study also aimed to determine whether a sperm hyperactivation functional test is effective in discriminating between Dohne Merino rams in terms of the resilience of their spermatozoa to heat stress. Semen samples were subjected to incubation at 38.5 ̊C for 30 minutes after the addition of 10mM procaine hydrochloride. Samples were evaluated at 0min, 15min, and 30min of incubation, and sperm viability, sperm morphology, and sperm acrosome integrity were quantified. There was no significant difference between the HR and LR groups for percentage live and abnormal acrosomes at all time intervals. There were significant differences between the HR and LR group for percentage abnormal spermatozoa at all time intervals. Significant individual differences were observed between the rams for sperm viability and morphology, but not for acrosome integrity when considering the entire 30 minutes of incubation. There was a faster rate in the reduction of quality for the LR group for abnormal spermatozoa compared to the HR group. The subpopulation structure of ejaculates should be considered when using induced hyperactivation as a sperm functional test, especially when ejaculation frequency is high. Simulations of the in-vivo environment of the female reproductive tract in an in-vitro environment may assist in more precise determination of fertilizing ability from heat stressed spermatozoa.