Ovarian follicular development in cattle selected for twin ovulations and births12
Journal of Animal Science
Ovarian follicular development in cattle selected for twin ovulations and births 2004. 82:459-471. J Anim Sci http://jas.fass.org/cgi/content/full/82/2/459 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by on ABSTRACT: Comparisons of numbers of antral ovarian follicles and corpora lutea (CL), of blood hormone concentrations, and of follicular fluid steroid concentrations and IGFBP activity were conducted between
... e conducted between cows selected (twinner) and unselected (control) for twin births to elucidate genetic differences in the regulation of ovarian follicular development. Ovarian follicular development was synchronized among cows by a single i.m. injection of PGF 2α on d 18 of the estrous cycle; six cows per population were slaughtered at 0, 24, 48, and 72 h after PGF 2α . Jugular vein blood was collected from each animal at PGF 2α injection and at 24-h intervals until slaughter. Ovaries of twinner cows contained more small (≤5 mm in diameter, P < 0.05), medium (5.1 to 9.9 mm, P < 0.05), and large (≥10.0 mm, P < 0.01) follicles and more (P < 0.01) CL than ovaries of controls. Follicular fluid concentrations of estradiol, androstenedione, testosterone, and progesterone reflected the stage of follicular development and were similar for twinner and control follicles at the same stage. Earlier initiation of follicular development and/or selection of twin-dominant follicles in some twinner cows resulted in greater concentrations of estradiol in plasma at 0, 459 24, and 48 h and of estradiol, androstenedione, and testosterone in follicular fluid of large follicles at 0 h after PGF 2α for twinner vs. control cows (follicular status × time × population, P < 0.01). Binding activities of IGFBP-5 and -4 were absent or reduced (P < 0.01) in follicular fluid of developing medium and large estrogen-active (estradiol:progesterone ratio > 1) follicles but increased with atresia. Only preovulatory Graafian follicles lacked IGFBP-2 binding, suggesting a possible role for IGFBP-2 in selection of the dominant follicle. Concentrations of IGF-I were twofold greater (P < 0.01), but GH (P = 0.10) and cholesterol (P < 0.05) were less in blood of twinners. Three generations of selection of cattle for twin ovulations and births enhanced ovarian follicular development as manifested by increased numbers of follicles within a follicular wave and subsequent selection of twin dominant follicles. Because gonadotropin secretion and ovarian steroidogenesis were similar for control and twinner cattle, enhanced follicular development in twinners may result from decreased inhibition by the dominant follicle(s), increased ovarian sensitivity to gonadotropins, and/or increased intragonadal stimulation, possibly by increased IGF-I.