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Reproductive Steroids in the Bovine. V. Comparisons of Fertile and Nonfertile Cows 0 to 42 Days after Breeding¹

Purdue University, Lafayette, Indiana 47907

Abstract

Urine and blood samples were collected from 40 dairy cows on days 0, 7, 14, 19, 28, 35 and 42 days after breeding if estrus was not observed prior to 42 days. The objective was to compare rates of excretion of estrogens in urine and jugular venous plasma levels of progesterone, luteinizing hormone (LH), corticosterone and cortisol in cows returning to estrus after breeding to pregnant cows. The cows were divided into four groups based on days to return to estrus, namely Group 1—less than 19 days; Group 2–19 to 24 days; Group 3–34 to 49 days; and Group 4—pregnant. The number of cows in each group was 10, 11, 10 and 9, respectively.

Rate of excretion of estrogen in urine was generally more variable in Groups 1 and 2 on day 0 and in Groups 1 and 3 on day 7 as compared to Group 4. Differences between days and groups were nonsignificant. Plasma progesterone increased and plasma LH decreased (P<.01) from day 0 to day 7. The highest average levels of progesterone within groups were observed on day 7 for Group 1, day 14 for Group 2, days 14 and 19 for Group 3 and day 42 for Group 4. Increases in LH occurred with decreases in plasma progesterone on day 14 in Group 1 and on day 19 in Group 2 preceding return to estrus in these groups. Plasma cortisol was significantly higher in Group 4 on day 0 than each of the other groups (P<.10 to 0.01) and higher (P<.05) in Groups 3 and 4 on day 7 than Groups 1 and 2. Plasma corticosterone did not vary significantly between groups or days. Based on partial regressions in a multiple regression analysis, estradiol-17ß was positively related to progesterone in Group 2 (P<.01) and Group 4 (P<.05) and negatively related to cortisol in Group 4 (P<.01). Cortisol and estrone were positively related in Group 1 (P<.05) and Group 2 (P<.01). Compared to pregnant cows, differences which may explain pregnancy failure were alternating low and high rates of excretion of estrogen in urine among individuals during the first 9 days after breeding (Randel et al., 1971b) in conjunction with decreased levels of progesterone in plasma as measured on day 7 after breeding.

¹ Journal Paper No. 4256, Purdue University Agricultural Experiment Station 47907. A contribution from Western Regional Project W-9S. 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 Fellow, Purdue Research Foundation, Grant No. 5076.

³ Present address: Sandoz Pharmaceuticals, Hanover, New Jersey 07936.

⁴ 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.