Serum Luteinizing Hormone and Estrogen Profiles before Puberty in the Gilt1

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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. Copyright © 1984. American Society of Animal Science. Copyright 1984 by American Society of Animal Science.

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