Relationship of progesterone in plasma and whole milk of buffaloes during cyclicity and early pregnancy.

Blood and milk samples were collected on alternate days from 5 cycling buffaloes on 16 occasions and 2 pregnant buffaloes on 13 and 8 occasions. The blood and milk samples were analysed for progesterone by sensitive direct radioimmunoassay (RIA) procedures developed in this laboratory. The calculated correlation values (r) between plasma and milk progesterone concentrations during cyclicity were 0.8143, 0.5454 and 0.8147 on 0 to 4, 6 to 14 and -6 to -2 days, prior to next oestrus (day 0 = day of oestrus) and the correlations for individual buffaloes during cyclicity were in the range of 0.82 to 0.89 for plasma and milk progesterone concentration. The correlation between milk and plasma levels during early pregnancy in buffaloes was very low (0.1472). The linear regression equation between milk (Y, ng/ml) and plasma (X, ng/ml) progesterone concentration was Y = 1.8 + 3.61X which indicated that the milk progesterone levels were about 4 times higher than those in plasma. It was concluded from this study that in certain situations, such as during cyclicity when large variations occur in corpus luteum activity, the milk and plasma progesterone concentrations from the same buffalo are highly correlated. However, the correlation is very poor when corpus luteum activity remains more or less unchanged, as seen during pregnancy.