Plasma LH concentrations for prepubertal, postpubertal, anestrous and cyclic ewes of varying fecundity.

Luteinizing hormone (LH) was measured in plasma samples collected at 15-rain intervals for 2 hr from 40 prepubertal Finn, Finn-cross (1/2), Rambouil let 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<.O1) 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<.O1), but was not correlated to plasma LH concentration within or among breeds. (