Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2010
Publication Date: 9/3/2010
Citation: Atkins, J.A., Smith, M.F., Macneil, M.D., Jinks, E.M., Geary, T.W. 2010. Contributions of follicle size to establishment and maintenance of pregnancy in suckled beef cows using reciprocal embryo transfer. 8th International Ruminant Reproduction Symposium Abstract #117. Interpretive Summary: abstract only
Technical Abstract: GnRH-induced ovulation of a small dominant follicle reduced pregnancy success in cattle. A reciprocal embryo transfer study was conducted at Fort Keogh from 2007 to 2009 in order to differentiate between follicular effects on pregnancy mediated through oocyte quality or uterine environment. Suckled beef cows (n = 1,166) were administered GnRH on d -9 (GnRH1), PGF*2a* on d -2, and GnRH (GnRH2) either with (donor cows; n = 810) or without (recipient cows; n = 354) artificial insemination on d 0. Single embryos (n = 394) or oocytes (n = 45) were recovered from the donor cows (d 7; ET) and all live embryos were transferred into recipients the same day. Embryos from cows that ovulated a small (< 12.5 mm) or large follicle (>= 12.5 mm) were transferred into cows that ovulated either a small or large follicle to remove co-linearity of follicle sizes pre- and post- day 7 of pregnancy; small to small (S-S; n = 71), small to large (S-L; n = 111), large to small (L-S; n = 122) and large to large (L-L; n = 50). Probability of successful fertilization increased with increasing diameter of the ovulatory follicle (P = 0.08) and serum concentrations of estradiol at GnRH2 (P =0.006). The probability of embryo survival up to d 7 increased with increasing serum concentrations of progesterone at PGF*2a* (P = 0.008) and follicle diameter at GnRH2 (P = 0.02). The stage of the embryo development was positively associated with serum concentrations of progesterone at ET (P = 0.05) but negatively associated with ovulatory follicle diameter at GnRH2 (P = 0.06). No direct effect of follicle size in either donor or recipient cows was detected for maintenance of pregnancy to d 27 or d 72 (P > 0.10). Probability of pregnancy at d 27 increased with increasing concentrations of estradiol at GnRH2 (P = 0.09) and progesterone at ET (P = 0.0005) in the recipients cows. There was no direct effect of donor serum concentrations of estradiol (GnRH2) or progesterone (ET) on pregnancy at d 27 (P > 0.10). In summary, increased ovulatory follicle diameter influenced the probability pregnancy through increased serum concentrations of estradiol on d 0, increased fertilization rate, increased incidence of a live embryo on d 7, and increased progesterone production from the resulting corpus luteum. Supported by NRI grant 2006-35203-17284 from USDA-CSREES.