Submitted to: Journal of Animal Science Supplement
Publication Type: Proceedings
Publication Acceptance Date: April 21, 2000
Publication Date: December 1, 2000
Citation: Echternkamp, S.E. 2000. Endocrinology of increased ovarian folliculogenesis in cattle selected for twin births. Journal of Animal Science. Available: http.www.asas.org/jas/symposia/proceedings/0935.pdf (E28). Accessed 1-28-05. Technical Abstract: Genetic selection for ovulation and twinning rate in cattle increased twinning rate to >50%. Ovaries of Twinner females had 200% more secondary preantral follicles, 50% more small (</=5 mm) and medium (6-12 mm) antral follicles, and a > 70% frequency of twin or multiple ovulatory follicles compared to unselected Controls. Primordial and primary follicles did not differ between genetic populations. Blood FSH and LH concentrations at estrus, after GnRH (25 or 150 ug) treatment, or after follicle aspiration did not differ between populations, except for increased LH release to GnRH in Twinners. Follicular fluid concentrations of estradiol and progesterone did not differ between dominant follicles of controls and twinners; whereas, blood estradiol and progesterone concentrations were related positively to number of dominant follicles and corpora lutea, respectively. Blood and follicular fluid IGF-I concentrations were greater in Twinner cows. Aspiration of follicles >/=5 mm in cyclic Twinner and Control cows initiated a transient increase in FSH, but not LH, followed by increased numbers of growing follicles and selection of twin dominant follicles in Twinners. Blood concentrations of FSH, LH, GH and insulin did not differ between cattle populations, but cholesterol was greater in Controls. Results suggest that the increased follicular recruitment and selection of twin ovulatory follicles in cattle selected for dizygotic twinning are associated with increased extra- and/or intraovarian IGF-I production; whereas, gonadotropin secretion was unaffected.