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Serum Prolactin and Growth Hormone in Holstein Bulls¹

Animal Reproduction Laboratory, Department of Dairy Science, Michigan State University, East Lansing 48824

ABSTRACT

Repeatabilities among three estimates of serum prolactin and growth hormone collected in 71 Holstein bulls within 10 days were .13 and .30. However, heritabilities of the serum hormone concentrations were not different from 0. In another experiment of 86 Holstein bulls, serum collected in July contained more than twice as much prolactin as serum collected in January whereas growth hormone was unaffected by months. Prolactin was unchanged whereas growth hormone decreased with age. However, logarithm base 10 of serum concentration of prolactin increased as age advanced. Neither hormone was significantly related to predicted difference. We conclude that simply measuring basal serum prolactin and growth hormone has little usefulness for estimating breeding values of cattle.

¹ Journal Article 6630 from the Michigan Agricultural Experiment Station.

² National Institutes of Health Predoctoral Fellow (5-F01-GM42220).