Abstract
Summary
Four heifers were exposed to 10° and 27° for 5 days after preconditioning to 21° in a controlled environment chamber. Serum prolactin decreased from 13 to 4 ng/ml during the 4-hr interval when ambient temperature was reduced from 21° to 10°. Prolactin increased from 8 to 22 ng/ml during the 3-hr period when ambient temperature was increased from 21° to 27°. During 5 days of chronic exposure to 10°, serum prolactin was 38% lower (P < 0.05) than during a control period at 21°; and while at 27°, heifers had twice the concentration of serum prolactin (P < 0.10) as those at 21°. Injection of 10 μg of thyrotropin releasing hormone (TRH) caused serum prolactin to increase within 5 min from 20 to 140 ng/ml in heifers at 27° and from 8 to 70 ng/ml in heifers at 10°. We conclude that ambient temperature influences basal and TRH-stimulated concentrations of serum prolactin in heifers.
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