Ovarian Activity, Circulating Hormones and Sexual Behavior in the Cat. II. Relationships During Pregnancy, Parturition, Lactation and the Postpartum Estrus

Abstract

Endocrine, ovarian and behavioral responses of cats throughout a mated estrus, pregnancy, parturition, lactation, weaning and the postpartum estrus were studied. Blood samples were analyzed for serum luteinizing hormone (LH), progesterone and estradiol-17β and laparoscopy was used to monitor follicle and corpus luteum (CL) development. Mean (± SEM) duration of the initial mated estrus (5.4 ± 0.4 days) was longer (P < 0.05) than the postpartum estrus (3.8 ± 0.5 days). Following 3 daily matings throughout each estrus, all cats (12/12) ovulated at the initial estrus and six of eight cats ovulated at the postpartum estrus. The ovulation to parturition interval was 64.2 ± 0.4 days (n=12) and the averag’e litter size was 3.3 ± 0.4 kittens (male:female sex ratio, 100:95). No queen demonstrated estrous behavior during the 6-week lactation interval. Postpartum laparoscopy indicated that four of 12 and three of 12 queens had more and fewer CL respectively, than were detected at the end of the mated estrus. Seven of eight queens demonstrated estrous behavior within 10–27 days (mean, 17.6 ± 2.3 days) following weaning. The eighth queen had a 133-day weaning to estrus interval. Although two of eight queens failed to ovulate at the postpartum estrus, average CL number for the ovulating queens (mean, 4.8 ± 0.3) was not different (P > O.05) from that observed at the initial mated estrus (mean, 4.9 ± 0.3). From the initial mated estrus through the first half of pregnancy serum LH and estradiol-17β profiles mimicked patterns reported earlier in queens mated with a vasectomized male and experiencing a prolonged luteal phase (Wildt et al., 1981). Both serum LH and estradiol-17β concentrations became more variable during the second half of gestation and a distinct estradiol-17β surge was detected within the 9-day interval before parturition in six of 12 queens. Individual cats varied considerably in their serum progesterone profiles with peak concentrations occurring from Days 11–60 (Day 1=first day of estrus and mating). Although progesterone titers approached nadir near term pregnancy in the majority of queens, baseline concentrations (< 1 ng/ml) were not a prerequisite for the onset of parturition. During the 6-week lactation interval, temporal fluctuations in serum LH and progesterone, as well as evidence of distinct ovarian follicle development were negligible. Low amplitude, episodic increases in estradiol-17β were measured at 10- to 18-day intervals during this time. Weaning resulted in a reflex elevation in serum LH and estradiol-17β in six of eight cats. Estradiol-17β profiles during the postpartum estrus were similar to the initial estrus. However, the postovulatory rise in progesterone at the postpartum estrus was delayed and progesterone concentrations measured during the first week after the postpartum estrus were less than half the magnitude detected at the initial estrus. These data: 1) integrate events associated with pregnancy and the postpartum interval of the cat; 2) suggest that suckling during lactation is a potent inhibitor of ovarian follicle development and gonadal and pituitary hormonal secretion, this negative effect being eliminated by weaning; and 3) indicate that reproductive efficiency is compromised at the postpartum estrus, as illustrated by delayed or abbreviated estrus, ovulation failure and depressed postovulatory elevations in serum progesterone.