INTRODUCTION Buffalo is the principal dairy animal in the developing countries of Asia and the mainstay of the Indian dairy industry, contributing over 60% of the total milk production. India produces about two-thirds of the world's buffalo milk and nearly half of the world's buffalo meat (FAOSTAT, 2005). Problem of silent heat coupled with late maturity, poor expression of estrus, irregular oestrous cycle, seasonality in breeding, anestrous, low conception rate, long postpartum interval, repeat breeding are some of the major constraints in buffalo productivity and improvement through artificial breeding (Madan, 1990). Silent estrus is one of the major impediments in understanding reproductive parameters and assisted reproduction in this species (Mondal et al., 2003b; Mondal and Prakash, 2003c; Mondal et al., 2008b). Buffalo tends to exhibit overt signs during night or early morning and most farmers are ignorant of physical signs of oestrous. The inherently suboptimal functioning of hypothalamo-hypophysial-gonadal axis and consequently low circulating hormones might be responsible for higher incidence of inactive ovaries and true anestrous in buffalo. Oestrus detection is also difficult in buffaloes due to lack of expert personnel, variation in duration of oestrous and reluctance of some teaser bulls to mate. Therefore, an understanding of oestrous expression mechanism in terms of endocrine modulations will form the basis for elucidating the causes of lower reproductive efficiency in buffalo.