Peripheral plasma levels of lh in the cow throughout the estrous cycle

Peripheral plasma levels of LH during the bovine estrous cycle were measured in 5 cows and one heifer by using double antibody radioimmunoassay. The sources of variability of basal LH-levels were analyzed in detail. The range of basal levels of LH WAS 0.3--3.5 Ng/ml. Between days 11 and 14 of the cycle the mean daily levels were lower in all cows by about 28% as compared with the remaining parts of the cycle. This did not seem to be directly influenced by changes in progesterone levels. A single peak of LH was observed around estrus. The magnitude of that preovulatory peak varied from 6.7 to 16.0 mg/ml, and lasted only a few hours.