Identification of potential intrafollicular factors involved in selection of dominant follicles in heifers

A surgical procedure to aspirate follicular fluid concurrently from individ ual follicles from the same heifer was validated and used to determine if i ntrafollicular amounts of estradiol, progesterone, inhibins, activin-A, fol listatins, and insulin-like growth factor binding proteins (IGFBP) differed for the future dominant compared with subordinate follicles during selecti on of the first wave dominant follicle. Heifers were subjected to surgery a nd aspiration of follicular fluid from the hive or three largest follicles on Day 3 of the estrous cycle (similar to 1.5 days after emergence). Ultras ound was used to determine the fate of each aspirated follicle after surger y. At aspiration, diameter of the future dominant and largest subordinate f ollicle was similar in heifers. However, estradiol was higher, whereas IGFB P-4 was lower in the future dominant compared with the largest or next larg est subordinate follicles. Also, the future dominant follicle in most cohor ts had the highest estradiol and lowest IGFBP-4 compared with future subord inate follicles. We concluded that: IGFBP-4 and estradiol may have key role s in determining the physiological fate of follicles during selection of th e first wave dominant follicle in heifers, and that both are reliable marke rs to predict which follicle in a growing cohort of 5- to 8.5-mm follicles becomes dominant.