Ovulation induction in anestrous bitches by pulsatile administration of gonadotropin-releasing hormone

Preliminary studies in anestrous Beagle bitches demonstrated that a single injection of gonadotropin-releasing hormone (150 micrograms) produced a rapid, physiological rise in serum estradiol lasting 1-3 days while progesterone remained below 1 ng/ml, whereas serial injections of FSH rapidly produced greater elevations in estradiol and a rapid rise in progesterone over 2 ng/ml. Consequently, attempts to induce fertile ovulation by means of pulsatile intravenous administration of GnRH (1 pulse/1.5 hours for 6-12 days; 0.04-0.43 micrograms/kg body weight/pulse) were conducted in eight anestrous bitches. Willingness to mate, serum progesterone levels and results of mating were monitored. In six of the eight bitches, vulval and vaginal signs of proestrus occurred by Day 2-4 after initiation of treatment (Day 0); but, two bitches showed negligible responses. In five of the six bitches in which proestrus was induced, behavioral (n = 4) and vaginal (n = 5) correlates of early estrus occurred by Day 5-7 of treatment and breedings occurred over a period of 4-12 days. Following onset of estrus, four of the five bitches had increases in serum progesterone levels between Days 14 and 18 after initiation of treatment (and 4-11 days after cessation of treatment); three of them became pregnant and whelped normal litters (ranging from 9 to 11 pups). The fifth bitch did not have elevated progesterone during the induced estrus, and upon return to estrus one month later was successfully bred and whelped a normal litter of 10 pups.(ABSTRACT TRUNCATED AT 250 WORDS)