Ovary

Associated and Independent Comparisons Between the Two Largest Follicles Preceding Follicle Deviation in Cattle

Abstract

Diameters of follicles and concentrations of follicular-fluid factors were studied in the two largest follicles (F1, F2), using F1 diameter groups in increments of 0.2 mm (equivalent to an interval of 4 h) and extending from 7.4 to 8.4 mm (12 heifers in each of six groups). Changes were compared between follicles, using the F2 associated with each F1-diameter group. Diameter deviation began in the 8.2-mm group, as indicated by a greater (P <0.05) diameter difference between F1 and F2 in the 8.4-mm group than in the 8.2-mm group. In the 8.0-mm group, estradiol concentrations began to increase (P <0.05) differentially in F1 versus F2, and free IGF-1 began to decrease differentially in F2 (approached significance, P <0.06). Combined for F1 and the associated F2, mean activin-A concentrations progressively increased (P <0.05) between the 7.6 and 8.2-mm groups and then decreased (P <0.05). Comparisons between F1 and F2 also were done by independently grouping F2 and using diameter groups at 0.2-mm increments for each follicle. In the diameter groups common to F1 and F2 (7.4, 7.6, 7.8, 8.0 mm), there was a group effect (P <0.003) for estradiol, involving an increase (P <0.05) between 7.6 and 7.8 mm averaged over F1 and F2. For free IGF-1, a fluctuation (significant increase followed by a significant decrease) occurred independently in F1 between 7.4-7.8 mm and independently in F2 between 7.0-7.4 mm. There were no independent changes for activin-A. Results indicated the following: 1) estradiol and free IGF-1 concentrations began to change between F1 and the associated F2 before the beginning of diameter deviation, 2) a mean transient elevation in activin-A was present in the two associated follicles at the beginning of the estradiol and free IGF-1 changes, 3) estradiol began to increase independently in both follicles at 7.6 mm, and 4) a free IGF-1 fluctuation encompassing an equivalent of 8 h occurred in both F1 and the independent F2 at different diameters.