The response of the bovine ovary to pregnant mares’ serum and horse pituitary extract

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Abstract
The response of bovine ovary to single subcut. inj. of pregnant mares'' serum (PMS) and horse pituitary ext. was studied. Mean follicular diam. (M.D.) and % follicles larger than 10 mm. were related to treatment. The threshold dose of PMS for quantitative effects was 1000-2000 i. u.; maximal rate of response at 3000-4000 i. u. The response bore no observed relation to the stage of estrous cycle at which inj. were given; except that ovulation followed PMS only when given in follicular stage of cycle. With pituitary extract, ovulation regularly occurred. Various qualitative changes were noted. Variable results are to be expected in field use of gonadotrophins in anestrous heifers and with over 2000 i. u. PMS there is danger of superovulation.