EFFECTS OF INTERMII"rENT INJECTIONS OF LHRH ON SECRETORY PATTERNS OF LH AND FSH AND OVARIAN FOLLICULAR GROWTH DURING POSTPARTUM ANOVULATION IN SUCKLED BEEF COWS 1,2

Changes in numbers of ovarian follicles and coincident secretion of pituitary gonadotropins were characterized in suckled, anovulatory beef cows injected iv with 500 ng of luteinizing hormone-releasing hormone (LHRH) every 2 h for 48 or 96 h, starting 21.4 +_ .4 d after parturition. Two hours after the last injection, all cows were ovariectomized. Compared with saline-injected controls, LHRH had no effect on baseline or overall concentrations of luteinizing hormone (LH) in serum (P> A0), but increased (P<.05) frequency and decreased (P<.05) amplitude of LH pulses. Luteinizing hormone-releasing hormone increased (P<.05) baseline concentration of follicle stimulating hormone (FSH) in serum and frequency of FSH pulses, but decreased (P<.05) pulse amplitude. Overall concentrations of FSH increased 20% (P<. 10). Exogenous LHRH did not affect diameter of the two largest follicles or numbers of follicles 1.0 to 3.9 mm, 4.0 to 7.9 mm or > 8.0 mm in diameter. These data suggest that increasing the frequency of episodic LH and FSH pulses in postpartum cattle by intermittent administration of LHRH did not increase mean circulating levels of LH, or alter size and numbers of ovarian follicles within the 96-h period of injections, Thus, induction of ovulation in anovulatory cows treated with low-dose injections of LHRH cannot be explained on the basis of an increase in mean concentrations of LH or numbers of antral follicles within 96 h after initiation of injections. (