Reaction of Cows Ovaries to GnRH Administration in Different Estrous Stages
Keywords:
cow, estrous cycle, GnRH, luteal phaseAbstract
Administration of GnRH in the luteal phase of estrous in dairy cows induces an increase of LH levels, with the modification of the growth waves of the ovarian follicles. GnRH induces ovulation or atresia of the dominant follicle and the recruitment of a new wave of follicular growth. The GnRH administration in the luteal phase of the estrous cycle induces growth waves synchronization of ovarian follicles, so that, a new wave of follicles started to grow at 5-6 days after administration. In our experiments, we administered 2ml Ovarelin (100 mcg GnRH), to three groups of cows (116 cows): in early luteal phase of the estrous cycle (days 4-5), in the middle of luteal phase (days 9-12), and late luteal phase (days 15-16). The rates of cows standing heat were 91.66% when GnRH was administered in early luteal phase, 95.22% when was administrated in the middle of luteal phase, and 73.68% in late luteal phase GnRH administration. After artificial insemination, the conception rates were 48.48% in early luteal phase, 52.5% at middle luteal phase and 46.42% in the late luteal phase of the estrous cycle.
References
Wolfenson, D., Thatcher, W. W., Savio, D. J., Badinga, L., Lucy, M. C., The effect of a GnRH analogue on the dynamics of follicular development and synchrinization of estrus in lactating cyclic dairy cows. Theriogenology, 1994, 42, 633-644.
Thatcher, W. W., Macmillan, K. L., Hansen, P. J., Drost, M., Concepts for regulation pf corpus luteum function by the conceptus and ovarian follicles to improve fertility. Theriogenology, 1989, 31, 149-164.
Crowe, M. A., Goulding, D., Baguisi, A., Boland, M. P., Roche, J. F., Induced ovulation of the first postpartum dominant follicle in beef suckler cows using a GnRH analogue. J. Reprod. Fertil., 1993, 99, 551-555.
Martinez, M. F., Adams, G. B., Berghfelt, D. R., Kastelic, J. P., Mapletoft, R. J., Effect of LH or GnRH on the dominant follicle of the first follicular wave in beef Heifers. Anim. Sci., 1999, 57, 23-33.
Guilbault, L. A., Lussier, J. G., Grasso, F., Matton, P., Influence of an analogue on follicular dynamics in cows pretreated or not with FSH-P. Theriogenology, 1990, 33, 240.
Twagiramungu, H., Guilbault, L. A., Dufour, J. J., Synchronization of follicular wanes with a GnRH agonist to increase the precision of estrus in cattle: a review. J. Anim. Sci., 1995, 73, 3141-3151.
Ryan, M., Mihm, M., Roche, J. F., Effect of GnRH given before or after dominance on gonadotropin response and the fate of that follicle wave in postpartum dairy cows. J. Reprod. Fertil., 1998, 21, 28.
Ginther, O. J., Wiltbanch, M. C., Fricke, P. M., Gibbons, J. R., Kot, K., Selection of the dominant follicle in cattle. Biol. Reprod., 1996, 55, 1187-1194.
Vasconcelos, J. L. M., Silcox, R. W., Rosa, G. J. M., Pursley, J. R., Withbank, M. C., Synchronization rate, size of the ovulatory follicle and pregnancy rate after syncronizarion of ovulation beginning on different days of the estrous cycle in lactating dairy cows. Theriogenology, 1999, 52, 1067-1078.
