Serum luteinizing hormone and plasma progesterone levels during the estrous cycle and early pregnancy in cows.

Abstract

Luteinizing hormone (LH) was measured in serum with a radioimmunoassay and progesterone was measured in plasma with a competitive protein binding assay throughout the cycle and early pregnancy in cows. Blood samples (162) were collectedduring five estrouscyclesand fiveperiods of early pregnancy from seven nonlactating dairy cows. LH concentrationsas high as 100 ng/ml (range 7-100 ng/ml) were obtained 3 to 6 hr afterthe onset of estrus.Elevated levelslastedfor 8 to 10hr. LH was below 1 ng/ml during most of the 20 to 25 days following estrusin both pregnant and nonpregnant cows. The concentrations of progesterone in plasma reached a peak on day 14 in pregnant cows and on day 16 in nonpregnant cows. Progesterone concentrationswere higher from days 10 to 14 in the pregnant cows than in the nonpregnant cows. The concentrations of serum LH and plasma progesterone were not associatedduring the estrous cycle or early pregnancy as determined by submitting the data to regression analyses.