Effect of photoperiod and castration on prolactin, testosterone and luteinizing hormone concentrations in male calves

Stanisiewski, E.P.; Chapin, L.T.; Petitclerc, D.; Tucker, H.A.

Journal of Animal Science 65(5): 1306-1311

1987


ISSN/ISBN: 0021-8812
PMID: 3693155
DOI: 10.2527/jas1987.6551306x
Accession: 001575695

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Abstract
After 8 wk exposure to 8 h of light per day, prolactin (PRL) averaged 18.3 ng/ml of serum in eight male calves. Four calves then received 16 h of light per day; 6 wk later (age 14 wk) PRL averaged 93.8 ng/ml of serum, whereas PRL averaged 36.9 ng/ml of serum in four calves maintained under 8 h of daily light. By wk 20, PRL was not different in calves exposed to 16 or 8 h of daily light, averaging 34.7 and 17.2 ng/ml serum. Testosterone averaged .43 ng/ml of serum at wk 8 but was greater at wk 14 in calves receiving 16 hof light daily when compared with controls receiving 8 h of light (1.92 vs. .97 ng/ml of serum). Testosterone concentrations were not different between photoperiod treatments at wk 20. Luteinizing hormone (LH) concentrations were unaffected by photoperiod. In a second experiment, four male calves were castrated at approximately 2 wk of age while four similar controls were left gonadally intact. After 8 wk exposure to 8 h of light per day, PRL averaged 12.3 ng/ml of serum in all calves. After 6 wk exposure to 16 h of light per day, PRL in serum increased in castrates to 48.0 ng/ml and in controls to 59.8 ng/ml. We conclude that serum concentrations of PRl and testosterone, but not LH, increased in bull calves receiving 16 h of light daily relative to calves receiving 8 h of light, and that the PRL response to photoperiod is independent of the testes. However, 16 h light-induced stimulation of serum concentration of prolactin is not maintained indefinitely.