Luteal Function and Embryo Survival in the Bovine

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Abstract
The ability of oxytocin injections to inhibit the development of the corpus luteum in the bovine was utilized to study the relationship between progesterone content of luteal tissue and embryo survival at 15 days after insemination in 70 Holstein heifers. Twenty of 27 untreated heifers (74.1%) had normal embryos and the average total progesterone in their corpora lutea was 270.2 [mu]g. The corpora lutea of the 7 untreated heifers from which embryos were not recovered had an average of 304.1 [mu]g of total progesterone. Eighteen of the 43 heifers (41.9%) injected subcutaneously with 7 U.S.P. units of oxytocin per hundred pounds of body weight per day had normal embryos and the average total progesterone content of their corpora lutea was 310.6 [mu]g. The total progesterone levels in the corpora lutea were not significantly different among these 3 groups of heifers. Fifteen oxytocin-treated heifers had a precocious ovulation prior to the 15th day and no embryos were recovered from this group; their corpora lutea contained only an average of 45.8 [mu]g of total progesterone (P< 0.01). The remaining 10 oxytocin-treated heifers had no embryos and their corpora lutea also contained significantly (P<0.05) less total progesterone (154.1 [mu]g) than the treated heifers having embryos. The level of [DELTA]4-pregnene-20[long dash]01-3-one was significantly (P< 0.01) higher in the corpora lutea of the untreated animals without embryos than in any other group. The data suggest that a threshold level of progesterone production represented by a luteal progesterone level of the order of 100 [mu]g is necessary for embryo survival at the 15th day. The 4 of 15 oxytocin-treated heifers that ovulated precociously without showing signs of estrus had little or no measurable progesterone in their corpora lutea.