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Reproductive Steroids in the Bovine. VII. Changes Postpartum^{1, 2,}

Purdue University, Lafayette, Indiana 47907

Abstract

JUST after calving the pituitary contains more follicle-stimulating hormone (FSH) and less luteinizing hormone (LH) than 20 to 21 days later (Labhsetwar et al., 1964; Saiduddin et al., 1968). The regressing corpus luteum (CL) of pregnancy and plasma from blood draining the ovaries contains very low levels of progesterone 1 to 4 days postpartum (Labhsetwar et al., 1964; Erb et al., 1968b). Rate of excretion of estrogen in urine decreases rapidly as measured at 0.5 days and 3 days after calving (Hunter et al., 1970) but does not decrease in a consistent way thereafter through 42 days postpartum (Erb, Randel and Callahan, 1971). During this latter period estrogen excretion rates generally are several times higher than observed at 0, 7 and 14 days of pregnancy (Randel and Erb, 1971) or during estrus cycles 60 or more days postpartum (Garverick et al., 1971). Although excretion of estrogen generally is high, a majority of otherwise normal cows do not show signs of behavioral estrus preceding the first postpartum follicle rupture (Morrow et al., 1966; Marion and Gier, 1968) and time to first ovulation is delayed in cows diagnosed as abnormal (Morrow et al., 1966; Callahan et al., 1971). The foregoing observations suggest that the endocrine balances required to support normal estrous cycles and to reestablish fertility are restored gradually after calving.

¹ Journal Paper No. 4386, Purdue University Agricultural Experiment Station 47907. A contribution from Western Regional Project W-95. This work was partially supported from a trust agreement between Purdue University and the Normandy Farm, New Augusta, Indiana, Mr. and Mrs. Herman C. Krannert, owners.

² We are indebted to Dr. L. E. Reichert, Jr., Emory University, Atlanta, Georgia for providing purified bovine LH and to Dr. G. D. Niswender, University of Michigan, Ann Arbor for providing anti-bovine LH antisera.

³ Present address: Sandoz Pharmaceuticals, Hanover, New Jersey.

⁴ Fellow, Purdue Research Foundation, Grant No. 5076.