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.