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Bovine Serum LH, GH and Prolactin following Chronic Implantation of Ovarian Steroids and Subsequent Ovariectomy¹

Michigan State University³, East Lansing 48824

Abstract

Holstein heifers were randomly assigned to be given: 1) No steroid (n=3); 2) a progesterone pessary (n=4); 3) four 17ß-estradiol implants in silastic (n=4); or 4) a progesterone pessary and 17ß-estradiol implants (n=4) 60 hr prior to ovariectomy. Implants were removed 8.5 days after beginning steroid treatment (6 days post-ovariectomy). Serum estradiol at 1 and 6 days after ovariectomy averaged 25 ± 5 and 22 ± 5 pg/ml in heifers receiving estradiol implants and 7 ± 1 and 4 ± 3 in heifers not receiving 17ß-estradiol. Serum progesterone averaged 3.2 ± 1.3 and 1.1 ± .1 ng/ml at 1 and 5 days post-ovariectomy in heifers bearing a progesterone pessary and .1 ng/ml in heifers without progesterone. Serum LH concentrations and variance were increased, relative to comparable values pre-ovariectomy, by 48-hr post-ovariectomy in all heifers except those receiving the combination of steroids. After cessation of steroid treatment, LH concentrations in heifers treated with estradiol plus progesterone increased during the next 7 days to values equal to controls. Serum GH and prolactin concentration was not significantly changed by steroid treatments. These data suggest that ovarian steroids do not influence serum prolactin and GH concentrations when present in blood at concentrations comparable to those found during the normal estrous cycle. However, the same concentrations of these steroids appear to act together to maintain basal serum LH concentration in the bovine.

¹ Published with the approval of the Michigan Agricultural Experiment Station as Journal Article No. 7037. Supported in part by NIH Grant No. 1 R01 AM-15899-01.

² Present address: Department of Dairy Science, University of Guelph, Guelph, Ontario, Canada.

³ Animal Reproduction Laboratory, Department of Dairy Science.