COMPARISONS OF ENDOCRINOLOGY AND BEHAVIORAL EVENTS DURING THE PERIOVULATORY PERIOD IN MEISHAN AND LARGE-WHITE HYBRID GILTS

Attainment of puberty, cycle lengths, ovulation rate and endocrinology during the periovulatory period were studied in Meishan (MS) and Euro pean Large-White hybrid (LW) gilts. The mean age at onset of puberty o f 115 days in MS (n = 20) gilts was younger (P < 0.001) than the 235 d ays in LW (n = 23). In the MS population studied, ovulation rate was n ot different (P > 0.1) during the third and fourth oestrous cycles, no r were there differences (P > 0.1) in the mean cycle length over the f irst three cycles. Overall changes in plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH) and oestradiol did not differ sign ificantly (P > 0.1) between the breeds (MS, n = 6; LW, n = 5) during t he periovulatory period, but plasma inhibin concentrations were signif icantly (P < 0.05) higher in the MS. The time intervals from the oestr adiol peak concentration and the onset of the LH surge until the onset of behavioural oestrus were significantly different (P < 0.005) betwe en the breeds, with oestrus occurring earlier in the MS. However, no d ifference (P > 0.1) was found between the groups when the intervals fr om the peak oestradiol concentration to the onset of the LH surge were compared. These results indicate differences between the breeds, part icularly in terms of the age of attainment of puberty and the timing o f the onset of behavioural oestrus relative to the oestradiol and LH s urges.