EMERGENCE AND DEVIATION OF FOLLICLES DURING THE DEVELOPMENT OF FOLLICULAR WAVES IN CATTLE

The nature of emergence and deviation of follicles during follicular w aves in cattle was studied in 3 experiments by re-examining data from previous projects. Wave emergence was defined as the day or examinatio n (when more than 1 examination per day) the future dominant follicle was 4 mm (Day 0 or Examination 0). Deviation was defined as the beginn ing of the greatest difference in growth rates between the 2 largest f ollicles and between 2 consecutive examinations. The search for deviat ion in an individual wave was done retrospectively from the examinatio n with the maximum diameter of the second largest follicle. In Experim ent 1, follicles were assessed ultrasonically for 28 waves every 8 h. The number of examinations that encompassed the emergence of all growi ng 3-mm follicles was 10.0 +/-0.5 (mean +/-SEM; equivalent to 3.3 d) a nd extended from mean Examination -3.1 +/-0.3 to mean Examination 6.0 +/-0.6. A mean of 24 growing 3-mm follicles was found, and the maximal attained diameters were 4 mm (46%), 5 mm (25%), and greater than or e qual to 6 mm (29%). More (P<0.05) 3-mm follicles at Examinations -2 an d -1 grew to greater than or equal to 6 mm than to 4 or 5 mn, whereas more 3-mm follicles at Examinations 2 to 6 grew to only 4 mm. On avera ge, the future dominant follicle appeared as a 3-mm follicle (Examinat ion -2.1 +/-0.2) 6 and 10 h earlier (P<0.03) than for the largest (Exa mination -1.4 +/-0.3) and second-largest (Examination -0.8 +/-0.4) fut ure subordinates, respectively. This result supported the hypothesis t hat the future dominant follicle has, on the average, an early develop mental advantage. In Experiment 2 (n=33 waves), data were normalized t o the day at the beginning of deviation (Day 2.8 +/-0.2) when the mean diameters of the dominant and largest subordinate follicle were 8.5 /-0.2 mm and 7.2 +/- 9.2 mm, respectively. This result suggests that t he follicle selected to become dominant, as manifested by deviation, i s the first follicle to develop to a decisive stage. In Experiment 3 ( n=19 waves), FSH concentrations were lower (P<0.05) on the day at the beginning of deviation (8.5 +/-0.5 ng/ml) than on the day before (10.1 +/-0.8 ng/ml), with no continuing decrease after deviation. This temp oral result suggests that the attainment of approximate basal levels o f FSH is a component of the deviation mechanism. (C) 1997 by Elsevier Science Inc.