Biology of Reproduction, Vol 22, 227-232, Copyright © 1980 by Society for the Study of Reproduction

Serum Hormone Concentrations and Their Relationships to Sexual Behavior at the First and Second Estrous Cycles of the Labrador Bitch

¹ Institute of Comparative Medicine and Department of Cell Biology, Baylor College of Medicine, Texas Medical Center, Houston, Texas 77030

Seven purebred Labrador bitches were monitored for sexual behavior at the first and second estrous cycles. Serum was analyzed for luteinizing hormone (LH), estrone (E₁), estradiol-l7 (E₂) and progesterone (P) concentrations. All hormonal data were normalized to the day of preovulatory peak LH (Day 0) for both cycles. Mean E₁ concentration during the week preceding Day 0 was greater (P<0.05) in the second cycle compared with that at the first cycle (42.0 ± 3.0 vs 29.0 ± 2.0 pg/ml), but the mean peak E₁ levels were not different (52.0 ± 16.0 vs 34.0 + 6.3 pg/ml). Both the mean peak E₂ concentration (54.0 ± 8.0 vs 28.0 ± 7.0 pg/ml) and the mean level during the week before peak LH (47.0 ± 4.0 vs 22.0 ± 4.0 pg/ml) were greater (P<0.05) in the second cycle compared with the first cycle. Mean serum LH concentration during the week before Day 0 (4.8 ± 0.9 ng/ml) in the second cycle was higher (P<0.05) compared with that of the first cycle (2.5 ± 0.7 ng/ml). The peak preovulatory LH (Day 0) for the second cycle was also higher (P<0.0l) than that of the first cycle (51.6 ± 6.9 vs 23.1 ± 4.2 ng/ml, respectively). The mean serum P concentration during the week before Day 0 was greater (P<0.05) in the second cycle (1.6 ± 0.1 vs 1.0 ± 0.3 ng/ml) but the mean P level during the second week following Day 0 was higher (P<0.05) in the first cycle (15.8 ± 2.0 vs 9.4 ± 0.8 ng/ml). The durations of proestrus (7.7 ± 0.5 vs 3.9 ± 0.7 days) and estrus (11.0 ± 1.1 vs 5.4 ± 0.4 days) were longer (P<0.01) in the second estrous cycle. The data suggest that 1) in general, serum hormone concentrations were elevated during the second cycle compared with the first cycle; and 2) durations of proestrus and estrus were longer during the second cycle. It appears that the shorter duration of sexual receptivity at the first behavioral estrous cycle in the bitch may have a hormonal basis.

Note:
ACKNOWLEDGMENTS The authors wish to acknowledge Dr. G. D.Niswender, Colorado State University, for supplying the ovine LH antibody and Dr. L. E. Reichert, Emory University, for providing the ovine LH (LER-1056-C2) for iodination and canine LH (LER-1685-1) for use as a standard. The authors also gratefully acknowledge Mr. Andrew Stewart and Ms. Barbara Alford for valuable technical assistance and Mr. Carrol Platz and Dr. David Wildt for critical evaluation of the manuscript.