Abstract
The studies were conducted on 12 lactating animals comprising of six Karan Swiss (KS) cows and six Murrah buffaloes in second and third lactation. At the start of experiment the cows had completed on an average 51 days in lactation and were yielding an average of 15.1 kg milk a day. The buffaloes had completed 53 days in lactation and were yielding an average of 11.6 kg milk a day. At fortnightly intervals jugular blood samples were drawn at morning, noon, evening and night hours. Plasma growth hormone concentrations were highest during morning and thereafter decreased. In both the species there was a definite trend in the change of growth hormone concentrations during the day. In general growth hormone concentration decreased as the stage of lactation advanced. The overall average values of plasma growth hormone in cows and buffaloes were 2.95 and 2.48 ng/ml which were not statistically different. With the advancing lactation, the decline in milk yields in both the species was positively correlated with the growth hormone concentrations.