Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 1996
Publication Date: N/A
Technical Abstract: Ovarian follicles and follicular fluid (FFL), estradiol (E), and progesterone (P) concentrations were compared on day 3, 5, 7, and 11 (estrus=day 0) between populations (POP) of cows selected (S) and unselected (U) for dizygotic twins. The 3 largest growing follicles present on day 3 were categorized as ORDER 1, 2, and 3 and monitored daily by ultrasonography until slaughter. Ovaries were obtained by slaughter. FFL and P were measured by RIA. Follicle diameter was larger (p<0.01) for S than U cows and differed among ORDER 1, 2, and 3 within S (13.7+/-0.2 vs. 11.5+/-0.2 vs. 9.4+/-0.3 mm, respectively) and U (12.2+/-0.2 vs. 8.4 +/-0.2 vs. 7.6+/-0.2 mm, respectively) cows (POP ORDER; p<0.01). Diameter of ORDER 1 and 2 follicles increased (p<0.01) from day 3 to 7 but ORDER 3 was unchanged by day (day ORDER; p<0.01). Maximum FFL E occurred on day 5 (229.7+/-16.7 vs. 69.5+/-15.7, 36.4+/-19.5, and 73.5+/-15.0 ng/ml for day 5 5vs. 3, 7, and 11; p<0.01) in both POP (POP D; p>0.1). FFL P was unaffected (p>0.1) by day, POP, ORDER, or their interactions. FFL E was similar for S vs. U cows in ORDER 1 (178.6+/-16.8 vs. 175.8+/-20.5 ng/ml) and ORDER 3 (60.5+/-25.2 vs. 9.7+/-21.4 ng/ml) follicles, respectively, but was higher in ORDER 2 follicles from S vs. U (150.3+/-17.4 vs. 38.9+/-20.5 ng/ml) cows (POP ORDER; p<0.01). Three-way interactions were not significant (p>0.1). Maximal aromatase activity occurred early in selection of the dominant follicle but declined during continued follicle growth and maintenance of dominance. Emergence of two or more large (>8 mm) estrogen- active follicles within a follicular wave suggests that selection of cattle for natural dizygotic twins has alter follicular dominance to allow selection of multiple dominant (or ovulatory) follicles within a wave.