PLASMA LH CONCENTRATIONS FOR PREPUBERTAL, POSTPUBERTAL, ANESTROUS AND CYCLIC EWES OF VARYING FECUNDITY

Luteinizing hormone (LH) was measured in plasma samples collected at 15-min intervals for 2 h from 40 prepubertal Finn, Finn-cross (1/2), Rambouillet and Hampshire ewes at 9, 13 and 17 wk of age and on day 5 of the 2nd 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.