Submitted to: International Conference on Farm Animal Endocrinology
Publication Type: Abstract Only
Publication Acceptance Date: January 25, 2002
Publication Date: N/A
Technical Abstract: Ovarian follicular waves of Twinner cows have a larger pool of small follicles (1-5 mm) and recruit and select more twin or multiple ovulatory follicles compared to unselected control cattle. Relationships among antral follicular development and FSH, LH, GH, and IGF-I secretion were compared after follicle ablation between Control and Twinner cows. Follicular fluid was aspirated by transvaginal ultrasonography from all antral follicles >5 mm on both ovaries of 12 Twinner and 12 Control cyclic cows on d 7 or 8 (estrus = d 0). Jugular blood samples were collected at 6-h intervals from 0 to 96 h after aspiration. FSH, LH, GH, IGF-I, and progesterone were measured in plasma by RIA. Follicular activity was monitored daily by transrectal ultrasonography. Data were analyzed by repeated measures analysis. Plasma FSH concentrations were increased (P < 0.01) within 6 h after aspiration, maximal at 24 h, and baseline by 72 h. Plasma IGF-I concentrations exhibited a small increase (P < 0.05), but LH and GH were unaffected (P > 0.1) by aspiration treatment. Plasma IGF-I was greater (P < 0.01) in Twinners vs Control cows (56.2 vs 38.1 ng/ml; SEM = 1.8). Plasma FSH (49.9 vs 44.5 ng/ml; SEM = 1.7), LH (1.26 vs 1.06 ng/ml; SEM = 0.04) and GH (6.4 vs 5.3 ng/ml; SEM = 0.7) did not differ between cattle populations. Plasma progesterone concentrations were proportional to number of functional corpora lutea. Ovulation rate was greater (P < 0.05) in Twinner vs Control cows after follicle aspiration. Results suggest that enhanced recruitment and selection of twin ovulatory follicles is not related to magnitude of endogenous gonadotropin secretion; but follicular response to FSH may be enhanced by greater IGF-I secretion in Twinner females.