Estrous cycle length in heifers was reduced significantly (P<0.01) by the following treatments: oxytocin (150 units daily) injected on day 3 to 7 (9.4 days), progesterone (100 mg. daily) injected on days 1 to 3 (13.6 days) or on days 2 to 6 (16.5 days). Corpora lutea were removed on day 8 from heifers injected with oxytocin on days 3 to 7 or with progesterone on days 2 to 6. Oxytocin treatment significantly reduced CL weight, progesterone concentration and 20β-ol concentration. Progesterone treatment reduced CL weight significantly but did not affect the concentration or total content of progesterone or 20β-ol. Progesterone was injected in combination with oxytocin and CL were removed on day 8 of the estrous cycle. The CL from heifers receiving the combination did not differ significantly in weight or hormone concentration from those in heifers receiving only oxytocin. These results caused the rejection of the hypothesis that exogenous progesterone might prevent the depletion of pituitary LH caused by oxytocin and thereby decrease the amount of luteal inhibition.
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Harms et al. (1969) studied this question.