Effect of suckling on basal and GnRH-induced LH release in post-partum dairy buffaloes

Suckling, a common practice in smallholder dairy-farming systems in the developing world, delays the onset of post-partum ovarian activity in dairy buffalo. The present study was designed to assess the effect of suckling on pituitary function in lactating buffaloes 25-35 days post-partum. Six suckled and nine non-suckled buffaloes were challenged intravenously with a bolus injection of GnRH (20 μg buserelin acetate; Receptal). Heparinized venous blood samples were collected at 15 min intervals for 2 h before and up to 4 h after GnRH for luteinizing hormone (LH) estimation. Pretreatment basal LH concentrations were similar in the suckled (0.6 ± 0.2 ng/ml) and the non-suckled (0.5 ± 0.1 ng/ml) buffaloes. All but one suckled buffaloes released a LH surge, starting 15-60 min post-GnRH treatment, which lasted for 180-225 min. While one suckled buffalo did not respond to GnRH, the LH response in the remaining suckled buffaloes was significantly less than in the non-suckled buffaloes in terms of peak LH concentrations (14.3 ± 2.7 ng/ml versus 26.2 ± 4.3 ng/ml) and area under the LH curve (1575.6 ± 197.4 mm2 versus 2108.9 ± 323.9 mm2). The LH response was least in suckled buffaloes challenged with GnRH while in the luteal phase of an oestrus cycle and with plasma progesterone concentration >1 ng/ml. In conclusion, suckling suppressed pituitary responsiveness to exogenous GnRH challenge in post-partum buffaloes.