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Behavioral, Ovarian and Endocrine Relationships in the Pubertal Bitch^{1 ,2,}

Veterinary Resources Branch, National Institutes of Health³, Bethesda, MD 20205

Abstract

Behavioral, ovarian and endocrine correlates were determined in seven bitches experiencing first estrus, and the results compared with previous data obtained on multiparous females. One or more atypical reproductive patterns were observed in certain bitches at the pubertal estrus. The ability of pubertal dogs to display normal reproductive relationships appeared to be related to age, because animals that exhibited normal sexual behavior and endocrine profiles tended to be older than females that produced aberrant patterns. For the latter group, atypical observations included lack of sexual receptivity and reduced or inconsistent patterns of circulating concentrations of estradiol-17β, luteinizing hormone (LH) or progesterone. Ovulation was confirmed in all four pubertal dogs subjected to laparoscopy, including two bitches that failed to demonstrate estrous behavior. In individual animals, it appeared that inadequate or sporadic elevations in titers of estradiol-17β during the preovulatory phase of the cycle were associated with reduced or abbreviated LH surge concentrations, and the latter were subsequently related to an absent or only minor preovulatory rise in serum progesterone. Reduced preovulatory estradiol-17β concentrations and a delayed increase in circulating progesterone were also associated with a lack of sexual receptivity. These results (1) suggest that hormonal insufficiencies or irregularities exist in certain bitches at the pubertal estrus and that such atypical activity appears more characteristic of the first than later adult estrous periods, and (2) are consistent with the theory that estrogen preconditioning and a decrease in the endogenous estrogen to progesterone ratio are important in the initiation of sexual receptivity in this species.

¹ The authors wish to acknowledge Dr. G. D. Niswender, Colorado State Univ., for supplying estradiol-17β (#244), progesterone (#337) antiserum and ovine LH antibody (#15); Dr. L. E. Reichert, Emory Univ., for providing the ovine LH (LER-1056-C2) for radio-iodination and the canine pituitary LH standard (LER-1685-1), and P. Schmidt, A. Stewart and S. Charman-Guthrie for their technical expertise. Names of commercial manufacturers and trade names are provided for identification only and inclusion does not imply endorsement by the National Institutes of Health, US Public Health Service or US Department of Health and Human Services.

² Portions of this study were conducted at the Institute of Comparative Medicine, Baylor College of Medicine, Houston, TX, with partial financial support from the Ralston Purina Co., St. Louis, MO.

³ Division of Research Services, Building 14G, Room 102.