Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: April 23, 1999
Publication Date: July 1, 1999
Citation: Echternkamp, S.E. 1999. Endocrinology of increased ovarian folliculogenesis in cattle selected for twin births [abstract]. Journal of Animal Science Supplement. 77 (Supplement 1):122. Technical Abstract: Genetic selection in cattle using an index of ovulation and twinning rate (Twinner) has increased the frequency of twin births to >50% and enhanced ovarian follicular development. Ovaries of Twinner females contain a twofold greater number of secondary preantral follicles, exhibit 50% more small (< or = 5 mm) and medium (6-12 mm) antral follicles, and have a >70% frequency of twin or multiple dominant (ovulatory) follicles compared to unselected (Control) females; numbers of primordial and primary follicles do not differ. Circulating FSH and LH concentrations at proestrus and estrus or after GnRH treatment or follicle ablation did not differ between populations, except for increased LH release to GnRH in Twinners. Ablation of all follicles >5 mm in Twinner and Control cyclic cows (estrus=d 0) initiated a transient increase in FSH (but not LH) followed by increased numbers of growing follicles and selection of multiple dominant follicles in Twinners, without population differences in FSH or LH. Circulating concentrations of insulin and cholesterol also do not differ between populations. Whereas, IGF-I concentrations are elevated in blood and follicular fluid of Twinner cows. Results suggest that increased follicular recruitment and selection in Twinner cows are not related to level of gonadotropin secretion, but are likely associated with increased intraovarian and(or) systemic IGF-I production. Preliminary results are suggestive of QTLs for ovulation rate on chromosomes 5 and 7.