Fertility in the male equine

Hardman, Kevin J (1985) Fertility in the male equine. PhD thesis, University of Glasgow.

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Abstract

The original aim of this study was to investigate whether hormone estimation could be used to diagnose the presence of cryptorchid testes in male equines. The initial study concluded that testosterone assay of blood samples taken before and after human chorionic gonadotrophin (HCG) administration, was the most reliable testosterone based test. However, this test was not ideal. Because of an overlap in the ranges of testosterone concentration in samples taken from stallions and geldings, diagnosis could not be reached if both the pre and post HCG samples contained testosterone concentrations in this overlap range. Therefore, this HCG stimulation test would occasionally fail to provide a diagnosis of whether testicular tissue was present, or not, in cases of badly behaved animals that appeared to be geldings. Moreover this test could not be used to differentiate whether an animal with one scrotal testis was a unilateral cryptorchid stallion, or a hemicastrate stallion. The use of the HCG stimulation test in these cases would merely prove that the scrotal testis was present. Because of these problems an alternative approach involving hormone estimation was sought. A subsequent study investigated whether the estimation of FSH in blood samples from animals suspected of possessing testes, could provide a more reliable diagnosis than the HCG stimulation test. This required the preparation of an assay for the estimation of FSH in blood samples. The levels of FSH in the peripheral circulation of stallions were found to be more stable than the levels of testosterone observed previously. Therefore, unlike testosterone, FSH levels in single blood samples could be taken as representative of the average daily concentration in that animal. Unfortunately, the results presented in this thesis suggested that, under some circumstances, blood samples from stallions and geldings could contain similar concentrations of FSH. This appeared to result from a trend towards higher levels of FSH in older stallions, and a trend towards lower levels of FSH in older geldings. In addition, levels of FSH in a young cryptorchid stallion with no scrotal testis and one abdominal testis were similar to those in true geldings. Therefore FSH estimation could not be used to differentiate between those animals with stallion like behaviour that possessed testes and those that did not possess testes. In addition, unilateral cryptorchids produced blood samples with levels of FSH similar to those found in normal young stallions. This was thought to result from compensatory hypersecretion of inhibin by the scrotal testis present in these cases. These results suggested that FSH estimation could not be used to differentiate the hemicastrate stallion from the unilateral cryptorchid stallion. This initial study of cryptorchidism led to an interest in the association between hormone levels and fertility and infertility in stallions. A stallion with a, single, undeveloped, abdominal testis, had peripheral circulating levels of testosterone similar to those found in normal stallions. This suggested that Leydig cell function was not affected by local changes in spermatogenesis. However, the results of the estimation of FSH in blood samples taken from this stallion with one abdominal testis, which showed no evidence of spermatogenesis, demonstrated that peripheral FSH concentrations may be affected by germinal epithelial dysfunction. In this case germinal epithelial arrest was accompanied by elevated peripheral levels of FSH. This could be explained by an inhibin feedback loop hypothesis. In addition, an older stallion that consistently ejaculated fewer spermatozoa during semen collection, also produced blood samples with higher levels of FSH. Both these results suggested that alterations to normal seminiferous epithelial function may result in an elevation of peripheral FSH levels. Vasectomy of a stallion resulted in no changes in the peripheral concentration of FSH. This suggested that infertility in a stallion exhibiting azoospermia, and normal levels of FSH, could be diagnosed as a case of obstructive disease of the excurrent ducts. Infertility associated with elevated peripheral FSH levels could be diagnosed as resulting from damage of the germinal epithelium of the seminiferous tubules.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Veterinary science, Animal sciences
Date of Award: 1985
Depositing User: Enlighten Team
Unique ID: glathesis:1985-76582
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 14:06
Last Modified: 19 Nov 2019 14:06
URI: http://theses.gla.ac.uk/id/eprint/76582

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