Alterations in hypophysial responsiveness to synthetic GnRH at different postpartum intervals in Murrah buffalo...

The objective of this study was to investigate the hypophysial responsiveness to GnRH at different intervals post partum in Murrah buffalo. Plasma LH and FSH levels were measured at 1 h before and upto 6 h subsequent to the administration of GnRH (1 ug/kg body weight) or saline on Days 2, 20 and 35 post partum in 2 groups of buffalo (n=4 each). Plasma progesterone levels were measured in samples collected once daily from Day 3 to Day 46 post partum. Pretreatment basal LH levels exhibited a progressive increase from Day 2 through Day 35 post partum, while the basal FSH levels increased only until Day 20 post partum. Following a highly subdued LH response to GnRH on Day 2 post partum, a 408% increase (P < 0.01) was observed in the total LH released in response to GnRH on Day 20 post partum, followed by a 20% reduction (non-significant) over Days 20 to 35 post partum. The interval from parturition was highly correlated with total LH released (r = 0.711, P < 0.01). Unlike LH, a substantial amount of FSH was released following GnRH treatment on Day 2 post partum, which was not significantly different from the FSH response on Days 20 and 35 post partum. The LH and FSH response to GnRH was not significantly different between animals in which luteal activity resumed and in those which showed no luteal activity post partum. While pointing to a dramatic enhancement in the hypophysial responsiveness to GnRH between Days 2 and 20 post partum, these results suggest that pituitary responsiveness to GnRH does not appear to be the limiting factor for resumption of estrous cycles by Day 35 post partum in Murrah buffalo.