Two days of pulsatile GnRH infusion beginning 4 days before weaning in sows initiates a wave of follicular growth that is not sustained after weaning

Intervals to estrus and ovulation in weaned sows depend partially on the diameter of ovarian follicles at weaning. The objective was to determine if follicular diameter in sows could be increased by a 48 h period of GnRH infusion before weaning and whether this pre-weaning growth would advance follicular development after weaning. The posterior vena cava was cannulated in eight sows at 10 ± 1 day after farrowing. Sows were randomly assigned to receive intravenous treatment with either 2 mL of GnRH (1 μg/mL; n = 4) or 2 mL of saline (n = 4) every 0.5 h for 48 h beginning 94 h before weaning. The average follicular diameter and the number of follicles within diameter classes were determined daily by ultrasonography. Serum LH concentrations increased on the first infusion day but serum LH was equal to control on the last infusion day (P < 0.077). The GnRH infusion increased the average diameter of ovarian follicles (P < 0.001). Serum estradiol increased (P < 0.001) and serum FSH decreased (P < 0.016) coincident with GnRH-induced follicular development but these changes were reversed within 24 h after the end of the infusion period. Follicles that grew in response to GnRH regressed and were replaced by a new population of follicles within 4 days after weaning. Within the experimental model for the present study, a GnRH infusion increased follicular growth in lactating sows but follicles could not be sustained beyond the end of GnRH infusion.