Graduate Thesis Or Dissertation
 

Effects of Maternal Treatment with Testosterone Proprionate in Ewes from Day 30-60 of Gestation on Male Offspring Potential Fertility

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9306t203q

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  • Prenatal exposure to excess androgens, testosterone in particular, has clear effects on potential ram fertility. Utilizing breeding soundness examinations in male sheep will assess the ram's potential ability to impregnate a certain number of healthy females during a defined breeding season. Identifying rams that have high breeding potential can provide a direct economic benefit to the producer. Previous studies have examined the critical period for prenatal androgen exposure on testicular development from day 30 to 120 of gestation. In these studies they have found lower body weights, smaller scrotal circumference, reduced motility and reduced sperm concentration. Other studies looked at depressed function of the hypothalamic-pituitary-gonadal axis, altered testicular cellular distribution and function as well as altered gene expression. The first study evaluated the dogma of the necessity to use a different stimulation technique when collecting semen from a ram by electroejaculation, than that described for bulls. The objective of this study was to evaluate two electroejaculation techniques for collecting semen in rams. Our hypothesis was that the "bull method" of electroejaculation used to collect semen from a ram would yield results similar to the traditional "ram method". Rams (n=48) were electroejaculated using either the "bull" method (n=24) or the "ram" method (n=24). There was no significant difference based on this particular group of rams between the "ram method" and "bull method". Both produced similar results with respect to efficacy of the method to produce a semen sample and quality of the samples collected when performing a breeding soundness exam. The objective of the second study was to determine the effects of prenatal androgen exposure over a brief duration early in the critical period of testicular development. We hypothesized prenatal treatment with testosterone proprionate between day 30 to 60 of gestation would reduce adult body weight, scrotal circumference, sperm motility, concentration, viability, and normal morphology and increase Leydig and Sertoli cell numbers and AMH, StAR, and CYP17 gene expression. At 18 months of age, breeding soundness examinations (BSEs) were conducted to assess fertility potential of control (n=12) and testosterone proprionate prenatally treated rams (n=12). Rams were then humanely euthanized with an overdose of pentobarbital and two 1 cm³ biopsies from each testis were obtained for histomorphometric analysis, immunohistochemistry, and qRT-PCR. The results of this experiment demonstrated that prenatal treatment with testosterone proprionate between days 30 to 60 of gestation affects the potential fertility of ram lambs. There was also a significant difference in scrotal circumference and sperm concentration between treated and control rams. The findings from this study are significant because they contribute to our understanding of how disruption of the fetal hormone environment alters the development of the testis. Both of these studies addressed potential fertility of rams, how it can be assessed and how it can be manipulated. The treatment of the first study did not definitely define the window of critical development exposure or pinpoint where the alterations to the testis had occurred during fetal development, further research is warranted.
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