Postpartum endocrinology and prospects for fertility improvement in the lactating riverine buffalo (Bubalus bubalis) and yak (Poephagus grunniens L.)

In many Asian countries the riverine buffalo is the major milk producing animal besides contributing towards draught power and meat production. The animal however suffers from inherent reproductive problems such as poor estrus expression and long calving intervals which limits its lifetime production. The yak is a seasonal breeder and the mainstay of highlanders and tribal populations inhabiting the inhospitable terrains of the Himalayan region. The factors responsible for its seasonality include poor nutrition, harsh climate and high altitude. Very little information is available on postpartum endocrinology in riverine buffaloes and even less so in yaks in relation to milk yield and cyclicity commencement. Our recent investigations on endocrine changes associated with cyclicity commencement in buffaloes (Murrah breed) showed a positive correlation between plasma prolactin concentrations and delay in postpartum cyclicity commencement. A significant correlation of plasma GH concentration with milk yield was also obtained. Monitoring cyclicity through milk progesterone analysis in buffaloes postpartum indicated that the incidences of silent estrus was low in winter months and very high in summer months — the overall annual mean being 37%. Preovulatory LH surges post-estrus occurred at different times resulting in ovulations at 28 to 60 h after onset of spontaneous estrus in buffaloes. Progesterone profiles in some yaks indicated cyclic activity even during non-breeding season. The positive correlation between plasma prolactin and melatonin indicates valuable evidence for their role in reproduction in this animal.