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Levels of Pituitary FSH and LH in Heifers from Birth through Puberty¹

Michigan State University³, >East Lansing

Abstract

Pituitary FSH and LH were determined in 65 heifers slaughtered in groups of five at monthly intervals from birth through 12 mo. of age. Average age at first estrus was 31.7 wk. and average estrous cycle length (20.5±0.6 days) did not change from first to subsequent cycles. Average weight of the whole pituitary increased from 0.69 gm. at birth to 1.80 gm. at 12 mo. Over 90%. of this increase was attributable to increases in the anterior lobes. Pituitary FSH concentrations were 1.7, 2.7 and 1.1 meg. equivalents NIH-FSH-S2 per mg. at 0, 1 and 2 mo. respectively, but did not change significantly thereafter. Pituitary LH concentrations (adjusted for stage of estrous cycle of post puberal heifers) increased four fold from 2.4 at birth to 9.1 meg. equivalents NIH-LH-B2 mg. at 3 mo. of age, varied considerably from 3 to 7 mo. and declined from 10.4 at 7 mo. to 4.8 mcg. equivalents at 12 mo. (P<0.05). Total pituitary LH and FSH contents paralleled the concentration values. These results reveal that puberty is associated with decreased levels of pituitary LH. Among 23 post puberal heifers, pituitary LH concentrations decreased from 8.7 before estrus to 1.1 mcg. equivalents per mg. (av. of day of estrus and day after estrus), and then increased almost continously toward the next estrus. Pituitary FSH concentrations decreased relatively less than and somewhat before LH during the week before estrus.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as paper No. 4130. This research was a part of a larger study on reproductive development of the pubertal female (U.S.P.H.S. research grant HD 01374). We acknowledge Dr. J. Jewel, Ayerst Laboratories, and Dr. R. Zimbelman, The Upjohn Company, for supplies of PMS and HCG, respectively. The Endocrinology Study Section, of the National Institutes of Health supplied the standard NIH-LH-B2 and NIH-FSH-S2.

² Present address: The Jackson Laboratory. Hamilton Station, Bar Harbor, Maine.

³ Animal Reproduction Laboratory, Department of Dairy.