Periovulatory endocrinology in high ovulating Meishan sows

The present study was designed to investigate the hormone profiles (oestradiol, LH, FSH, inhibin, progesterone) in high ovulating Meishan sows (MS; n = 9) and in contemporary Large-White hybrid control sows (LW; n = 9) during the follicular phase, the periovulatory period and the early luteal phase. Ovulation rate was higher in MS than LW animals (23.7 and 16.6 respectively; P < 0.001) and overall was correlated with the area of the oestradiol peak (P < 0.05) and inhibin concentrations (P < 0.05). Both the duration of and the area of the oestradiol peak were greater in MS than LW (P < 0.01; P < 0.02), as were inhibin concentrations both before and after the LH surge (P < 0.05). Neither basal nor peak concentrations of LH or FSH differed between the breeds (P > 0.05), although FSH concentrations were correlated with the area under the oestradiol peak (P < 0.05). Finally, the time-interval from the onset of the LH surge until the rise in plasma progesterone was shorter in MS than LW (54.5 and 74.3 h respectively; P < 0.01). In conclusion, these results show for the first time that the higher ovulation rate in MS is associated with enhanced oestradiol and inhibin secretion with no significant difference in LH or FSH concentrations. The more rapid luteinization response to the LH surge by MS in terms of plasma progesterone concentrations may be important in ensuring the high level of embryo survival in this breed.