Masters Theses

Date of Award

5-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Bert H. Erickson

Committee Members

A.B. Chestnut, H.G. Kattesh

Abstract

Two experiments were conducted to determine the effect of fescue infestation with the endophytic fungus, Acremonium coenophialum plus zeranol and endophyte-infested fescue alone on testicular development and hormonal secretions in the bull. Bulls were assigned to pastures infested with the fungus at control (0%), Low (50-70%), and High (80-84%) levels. In the first experiment, bulls were implanted at birth with zeranol and every 90 days thereafter.

Assessment of the effects of treatment on testicular development and the ability of the pituitary and testis to respond to GnRH challenges were determined. Gonadotropin releasing hormone (GnRH) challenges were effected when the bulls were 3, 5, and 8 months of age. In the second experiment bulls were removed from the pastures when they were 8 months old and injected with GnRH at 12 months of age to determine the late effects of the fungus. Jugular blood was collected at 0, 1, and 2 hours after GnRH injection and plasma was assayed for follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), androstenedione (δ4A) and prolactin (PRL). Bulls were castrated at 7 months of age in the first experiment, in the second experiment bulls were hemicastrated at either 3 or 8 months of age. Testis were weighed, measured, and prepared for histological evaluation. Cross-sections of seminiferous tubules were evaluated for the number of Sertoli cells (SC) and number of A-spermatogonia. In the 8 month-old testis, sections were evaluated for percentage of tubular cross sections occupied by the various generations of germ cells.

PRL secretions were significantly reduced (P<0.05) by fungal infestation in the zeranol and nonzeranol implanted bulls.

Serum LH levels were significantly reduced (P<.01) by fungal infestation when the bulls were implanted with zeranol. FSH levels were also reduced by fungal infestation in the zeranol-treated bulls (P<0.06). Gonadotropins in the nonzeranol treated bulls may have been reduced by the fungus (P>0.10). Testosterone levels were not affected by fungal infestation except at 3 months of age, where they were significantly reduced (P<0.01) in the nonzeranol treated bulls. Androstenedione levels were not affected by the fungus at any age studied.

Testicular weights were significantly lower in bulls treated with zeranol (P<0.07) and a trend toward lowered testes weights was seen in the nonzeranol treated bulls (P>0.10). Sertoli cell number was significantly reduced in both the zeranol treated bulls (P<0.01) and nonzeranol treated bulls (P<0.05). Number of A-spermatogonia was not affected by the endophyte but percentage of cross sections with mature spermatids were significantly (P<0.03) higher in the control group.

It is concluded that feeding infested fescue significantly reduced PRL levels in the bull. Fungal infestation significantly affected gonadotropins secretion in the zeranol treated bulls and they also reduced in the nonzeranol treated bulls but the difference was not significant. Testosterone secretion was reduced in the treated bull in the early prepubertal period in the nonzeranol treated bulls. Testicular weights and Sertoli cell number were decreased by fungal ingestion both with and without zeranol. Also, testicular development was delayed by fungus as evidenced by the histological evaluation. Decrements in number of Sertoli cells could lead to a permanent impairment of testicular function.

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