Effect of photoperiod and castration on prolactin, testosterone and luteinizing hormone concentrations in male calves.
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 h of 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 concentrations of prolactin is not maintained indefinitely.
Dept. of Anim. Sci., Michigan State University, East Lansing 48824.
E P
EP
Stanisiewski
L T
LT
Chapin
D
D
Petitclerc
H A
HA
Tucker
D000818:Animals; D002417:Cattle / Q000502:physiology*; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood* / Q000378:metabolism; D008297:Male; D009919:Orchiectomy / Q000662:veterinary*; D010507:Periodicity; D011388:Prolactin / Q000097:blood* / Q000378:metabolism; D013739:Testosterone / Q000097:blood* / Q000378:metabolism
D013739:Testosterone; D011388:Prolactin; D007986:Luteinizing Hormone