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Plasma LH Concentrations for Prepubertal, Postpubertal, Anestrous and Cyclic Ewes of Varying Fecundity^{1, 2,}

U.S. Department of Agriculture, Clay Center, Nebraska 68933

Abstract

Luteinizing hormone (LH) was measured in plasma samples collected at 15-min intervals for 2 hr from 40 prepubertal Finn, Finn-cross (1/2), Rambouillet and Hampshire ewes at 9, 13 and 17 weeks of age and on Day 5 of the second estrous cycle after puberty. Blood samples were collected at 20-min intervals from 40 yearling and 20 mature ewes of the same breeds during anestrus and on Day 5 of the estrous cycle. Ovulation rates were determined by laparotomy on Day 5 of the estrous cycle.

The plasma LH pattern for the prepubertal females was characterized by pulsatile LH releases which decreased (P<.01) in magnitude with advancing age. Overall mean plasma LH concentration for the yearling ewes was higher (P<.01) than for the mature ewes (2.39 vs 1.38 ng/ml). Plasma LH concentrations for the yearling ewes were higher (P<.05) at mid-anestrus than late anestrus. Ovulation rate was significantly higher for the Finn ewes (lambs, P<.05; yearlings, P<.01), but was not correlated to plasma LH concentration within or among breeds.

¹ Cooperation of the Nebraska Agricultural Experiment Station, University of Nebraska, Lincoln, is acknowledged.

² Appreciation is expressed to Dr. D. J. Bolt, U.S.D.A., ARS, Beltsville, Maryland, for antiserum to ovine LH; Dr. L. E. Reichert, Jr., Emory University, Atlanta, Georgia, for purified ovine LH(LER-1056-C2) and the Endocrine Study Section, NIH, Bethesda, Maryland, for ovine LH (NIH-LH-S18).

³ U.S. Meat Animal Research Center, Agricultural Research Service.