Effects of Zeranol on Some Reproductive Traits in Beef Bulls (Semen, Histology, Hormones)

The objectives of this experiment were to determine the effects of zeranol on some reproductive traits in beef bulls from 9 to 20 months of age. Three groups with 5 bulls per group were employed. Group I served as a control group. Group II was implanted with 36 mg zeranol (RALGRO) at birth, 3, and 6 months of age. Group III was implanted with 36 mg zeranol every 3 months from birth through 18 months of age. Zeranol reduced the release of GnRH-induced release of LH, increased secretion of FSH in response to GnRH, and suppressed synthesis of testosterone by Leydig cells in response to GnRH-induced release of LH and hCG. However, pituitary and Leydig cell function recovered from the effects of zeranol in a similar manner in both implanted groups with increasing age. Zeranol also reduced testicular development and serving ability (the ability of the bull to serve an artificial vagina or a heifer). However, both of these variables tended to recover as the bulls aged. Semen quality was low in the implanted groups and did not improve with increasing age. Samples of spermatozoa taken from the cauda epididymidis showed that implanted groups had a higher incidence of certain sperm abnormalities than the control group. No differences were found in testicular and vesicular gland weights and penis length at 20 months of age. Epididymal weight, however, was greater in the group III bulls. Histological examination of the genital organs showed that zeranol induced degenerative changes in the testes, induced adenomyosis and sperm granulomas in the cauda epididymidis and markedly altered the structure of the ampullae, vesicular glands, prostate, and bulbourethral glands. Based on the results from this study, it can be concluded that transient or continuous implantation of zeranol in bull calves resulted in a temporary imprint on pituitary and Leydig cell function. Consequently, testicular development and serving ability also were affected in a transient manner. Zeranol implantation also decreased semen quality, increased the incidence of certain sperm abnormalities in the cauda epididymidis, and induced lesions in the genital tract.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Veterinary Medical Science

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Deschamps, Joao Carlos

• Biology, Veterinary Science

Identifier

(UMI)AAI8409764

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/71308