Serum luteinizing hormone and estrogen profiles before puberty in the gilt

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 greater than or equal to 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, mean +/- SE) at age 7 (1.0 +/- .1) was greater (P less than .01) than at ages 2, 3, 4 and 5 (6 +/- .1) but not ages 1 and 6 (.8 +/- .1).(ABSTRACT TRUNCATED AT 250 WORDS)