Effect of the Uterus on Subnormal Luteal Function in Anestrous Beef Cows

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Abstract
The effect of the uterus on luteal lifespan and pattern of secretion of progesterone following early weaning of calves from anestrous beef cows was studied. Calves were weaned from 15 anestrous beef cows 23 to 33 d postpartum, and cows were allotted to a control (sham surgery, n = 8) or a hysterectomy (n = 7) group, with surgery performed at weaning. Cows in the hysterectomy group were injected (im) with 25 mg prostaglandin F2α (PGF2α) approximately 20 d after first estrus (d 0). The interval from weaning to estrus was longer (P<.05) for the hysterectomy group (10.4 ± 1.6 d) than the control group (6.2 ± .5 d). In the control group, the first estrous cycle (8.8 ± .3 d) was shorter (P<.01) than the second estrous cycle (20.2 ± .5 d). Following first estrus in the hysterectomy group, cows were not detected in estrus until after injection of PGF2α and did not return to estrus. From d 0 to 5, mean concentrations of plasma progesterone were similar (P>.05) between groups for both estrous cycles; after d 5 of estrous cycle 1, concentrations of plasma progesterone decreased in the control group. Within the hysterectomy group, the pattern of secretion of progesterone from d 0 to 16 was similar after the first and second estrus. Furthermore, there was no difference in the pattern of secretion of progesterone from d 0 to 16 between hysterectomy (first or second estrous cycles) and control (second estrous cycle) groups. These results suggest that by d 6 after first estrus, the uterus has a luteolytic effect on the corpus luteum in cows that have had their calves weaned early. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science