An ultrasonographic study of ovarian antral follicular dynamics in prepubertal gilts during the expected activation of the hypothalamo-pituitary-ovarian axis.

Daily transrectal ultrasonography was carried out in eight 4-5-month-old Polish Large White×Polish Landrace gilts for 42 days to monitor the growth of individual ovarian antral follicles≥2 mm in diameter. In total, 52.4±16.2 and 123.0±6.7 follicles per gilt (mean±SD) that grew to ≥4 mm were identified during the first and second 21-day study periods, respectively (P<0.01). Four follicular waves (defined as the synchronous growth of a group of follicles from 2-3 mm to ≥4 mm) emerged during the first period, and five waves emerged during the second period. The maximum diameters attained by the largest follicles of waves were 5.7±0.6 and 7.0±0.5 mm (first and second periods, respectively; P<0.01). The present results provide direct evidence for the rhythmic, wave-like pattern of antral follicle recruitment in prepubertal gilts. The number of follicles and maximum diameter they attain increase significantly during the expected activation of the hypothalamo-pituitary-ovarian axis in prepubescent gilts.