Date of this Version
Changes in plasma and follicular fluid concentrations of inhibin were examined in sows after weaning at 28-32 days post partum. From 0 to 48 h after weaning, inhibin concentrations were 200-300times higher in follicular fluid from small ( < 4 mm) and medium-large( ≥4 mm) follicles than in ovarian venous plasma. Inhibin concentrations increased in follicular fluid from medium-large follicles at 24 and 48 h after weaning; concentrations in ovarian venous plasma were positively correlated with the number of medium-large follicles (r= 0·40)and with ovarian venous plasma concentrations of oestradiol (r= 0·61).Blood samples were collected for 30 days from sows (n=6) that exhibited oestrus within 5 days after weaning and from sows (n=5) that remained anoestrous for 11 days after weaning. Plasma inhibin concentrations rose in oestrous and anoestrous sows by 12 h and continued to rise for 60 h after weaning. Plasma inhibin concentrations rose further and were higher at 3·5-4·5days after weaning in oestrous sows than in sows that remained anoestrous. After oestrus, plasma inhibin concentrations declined. At weaning, plasma concentrations of follicle-stimulating hormone (FSH) were higher in sows that subsequently exhibited oestrus than in sows that remained anoestrous. After weaning, plasma concentrations of FSH declined in both groups, reached a nadir at 2·5days, and increased gradually in anoestrous sows; oestrous sows exhibited an FSH surge at oestrus. Plasma FSH returned to preweaning concentrations in both groups of sows at Days 7-8.The results demonstrated dynamic changes in plasma concentrations of FSH and inhibin in sows after weaning; an inverse relationship of these, with the exception during the preovulatory surge of FSH, typifies the porcine oestrous cycle.