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Luteal Function as Related to Pituitary and Ovarian Cytology and Embryo Development in the Bovine¹

Department of Animal Husbandry and New York State Veterinary College Cornell University, Ithaca, New York

ABSTRACT

Embryos recovered 15 days after insemination from 20 of 27 untreated Holstein heifers and those recovered from 18 of 43 heifers treated daily with 7 U.S.P. units of oxytocin per hundredweight per day did not differ in total length, embryonic disc size, or mesodermal development attained. No embryos were recovered from animals with less than 100 µg. of total progesterone in their corpora lutea; normal embryo development appeared possible when the level of luteal progesterone was above this figure. The weights of the corpora lutea of the 15 oxytocin-treated heifers which had precocious ovulations were significantly (P < 0.01) reduced, and these corpora contained few normal luteal cells. Ten cystic corpora lutea were found in treated heifers and one in an untreated heifer. These cystic corpora lutea were all formed after ovulation; the cysts were 7 mm. or more in diameter and were separated from the surrounding luteal cells by fibrous tissue. Only two heifers with cystic corpora lutea had embryos. Low levels of progesterone were found in cystic corpora lutea, except in one heifer that had a normal embryo. Although an occasional cystic corpus luteum can produce enough progesterone to maintain an embryo until the 15th day, most of them appear to produce little progesterone and they are not likely to be associated with live embryos. The gonadotrophin-producing delta cells in the anterior pituitary were degranulated in some of the heifers which ovulated precociously and in the control heifers that did not have embryos.

¹ Supported in part by funds provided by the regional research project NE-41 entitled Endocrine Factors Affecting Reproduction and Lactation in Dairy Cattle, a cooperative study by Agricultural Experiment Stations in the Northeast and the Dairy Husbandry Research Branch, ARS-USDA.

² Present address: Department of Endocrinology, Wm. S. Merrell Co., Division of Richardson-Merrell Inc., Cincinnati, Ohio.