Abstract
Summary
Prolactin in sera of four cows subjected to 30 min of continuous milking increased from 28 ± 9 ng/ml before milking to a peak of 290 ± 29 ng/ml at 20 min, and averaged 229 ± 32 ng/ml at 30 min. In comparison with 25 cows maintained in the absence of their offspring on Day 2 postpartum, 23 cows maintained immediately adjacent to their calves (suckling not permitted) decreased basal-, milking-, and TRH-induced release of prolactin by 68, 69, and 29%, respectively, on Days 3 to 5 postpartum. We conclude that direct tactile stimulation of teats maintains increased secretion of prolactin, whereas presence of the calf immediately adjacent to their mothers but without suckling, does not stimulate secretion of prolactin. Indeed, the presence of the calf may be inhibitory to the secretion of prolactin in lactating cows.
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