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Serum Luteinizing Hormone and Estrogen Profiles before Puberty in the Gilt¹

University of Georgia, Athens 30602 and and US Department of Agriculture, Athens, GA 30613

Abstract

The hypothesis that an increase in serum luteinizing hormone (LH) concentration occurs before the onset of puberty in the gilt was tested. Blood samples were collected from 14 gilts, 166 d of age and 72.6 ± 1.8 kg body weight, every 15 min for 8 h 1 d after jugular cannulation. Gilts were checked daily for estrus with a boar. The sampling procedure was repeated 21 and 33 d later, by which time three gilts had attained puberty (first estrus with continued regular estrous cycles), and then every 7 d thereafter until an additional five gilts attained puberty. Serum LH and estrogen (E) concentrations were quantitated by radioimmunoassay. Bleeding periods were grouped into seven common physiological ages before puberty; age 1 57 d (n=4), age 2 = 43 to 50 d (n=5), age 3 = 31 to 38 d (n=4), age 4 = 22 to 26 d (n=5), age 5 = 17 to 19 d (n=4), age 6 = 10 to 12 d (n=5) and age 7 = 3 to 5 d (n=5). Mean serum LH concentration (ng/ml, x ± SE) at age 7 (1.0 ± .1) was greater (P<.01) than at ages 2, 3, 4 and 5 (.6 ± .1) but not ages 1 and 6 (.8 ± .1). Number of LH peaks/8 h (x ± SE) at age 7 (5.8 ± .9) was greater (P<.03) than at all previous ages (2.8 ± .3) and was greater (P<.03) at age 6 (4.0 ± .3) than at both ages 1 and 2 (2.1 ± .1). The LH peak amplitude (ng/ml, x ± SE) decreased (P<.03) from 1.8 ± .1 at age 1 to 1.3 ± .1 at age 7. Serum E concentration (pg/ml, x ± SE) at age 7 (14.0 ± 1.6) was greater (P<.05) than at ages 1, 2, 3 and 4 (9.4 ± .6), at age 5 (11.1 ± .9; P<.10) and at age 6 (10.8 ± 1.7; P<.06). Onset of puberty in the gilt was preceded by a significant increase in serum concentrations of both LH and E. The LH secretion immediately preceding puberty was characterized by an increased frequency of lower amplitude LH release compared with previous ages.

¹ This research was supported by State and Hatch funds allocated to the Georgia Agr. Exp. Sta. and by USDA funds. The authors thank Dr. Terry E. Kiser and Dr. Russell D. Page, Dept. of Anim. and Dairy Sci., Univ. of Georgia, for their advice in conducting this research and Sharon B. Tillman for preparing this manuscript. The authors gratefully acknowledge and thank Dr. Leo E. Reichert, Jr. of Albany Medical College, Albany, NY, for providing purified LH used in our radioimmunoassay, and Dr. Dennis R. Marple, Auburn Univ., Auburn, AL, for supplying the estrogen antiserum. Appreciation is extended to Mary A. Hart, Bennett Johnson and Doris M. Powell for their excellent technical assistance.

² Dept. of Anim. and Dairy Sci., Univ. of Georgia, Athens 30602

³ Anim. Physiol. Res. Unit, USDA, ARS, Richard B. Russell Agr. Res. Center, Athens, GA 30613

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