Title: Determinants of embryo development and quality in beef cattle: Effect of pre-ovulatory follicle size, CL volume, and serum concentrations of progesterone Authors
|Atkins, Jackie -|
|Smith, Mike -|
Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 3, 2009
Publication Date: July 10, 2009
Citation: Atkins, J.A., Smith, M.F., MacNeil, M.D., Geary, T.W. 2009. Determinants of embryo development and quality in beef cattle: Effect of pre-ovulatory follicle size, CL volume, and serum concentrations of progesterone. Society for the Study of Reproduction Annual Meeting. Online only. Technical Abstract: Previous research indicates cows ovulating a small dominant follicle (<_ 12 mm) had lower pregnancy rates than cows ovulating a large follicle (> 12 mm). We hypothesized cows ovulating a small follicle would have delayed embryo development and decreased embryo quality. Objectives of this study were to determine 1) the relationship between follicle size at GnRH induced ovulation, CL volume, and serum concentrations of progesterone (P4) 7 d later and 2) effects of ovulatory follicle size, CL volume, and P4 on embryo stage and quality 7 d after AI. Lactating multiparous beef cows (n=931; 644 donor and 287 recipient cows) were synchronized for single ovulation embryo transfer (d7) with the CO-Synch protocol (GnRH1 on d-9, PGF2a on d-2, and GnRH2 with timed AI on d0). Diameter of the ovulatory follicle (d0), CL, and lumen of the CL (d7) were determined using transrectal ultrasonography. The functional CL volume was calculated by subtracting the lumen volume from the total CL volume. Embryos recovered from donor cows were assessed for stage of embryo development (1 to 7; where 1 = unfertilized oocyte and 7 = expanded blastocyst) and quality (1 = excellent to good and 4 = dead or degenerate) according to the IETS guidelines. The effects of follicle size (d0), serum concentrations of progesterone (d7), functional CL volume (d7), and embryo age (time from GnRH2 until embryo grading) on embryo stage and quality were analyzed using a multiple regression model. The size of the pre-ovulatory follicle in both donors and recipients was positively correlated with the functional CL volume and P4 (r = 0.45 and 0.29, respectively; P < 0.001). Functional CL volume was positively correlated with P4 (r = 0.36; P < 0.001) in donors and recipients. There were 37 oocytes and 319 embryos recovered, of which 13, 36, 189, 71, 9, and 1 of the embryos were stage 2, 3, 4, 5, 6, and 7, respectively. The majority of the embryos recovered were quality grade 1, followed by 2, 3, and 4 (196, 75, 29, and 19, respectively). As the age of the embryo increased so did the stage of development (P= 0.02) but follicle size, functional CL volume, and progesterone did not affect embryo stage (P = 0.32, 0.20, and 0.44, respectively). There was a tendency for better quality embryos recovered from cows with larger follicles (P = 0.09) but functional CL volume, P4, and embryo age did not affected quality grade (P= 0.90, 0.53, and 0.30, respectively). When only transferrable embryos were included in the analysis, embryo stage increased as follicle size, functional CL volume, and embryo age increased (P< 0.01) and embryo quality improved as follicle size increased (P = 0.05). In summary, follicle size at day of AI was positively correlated with P4 and functional CL volume 7 d after AI. When all embryos were analyzed, neither follicle size, functional CL volume, nor P4 affected embryo development but follicle size may have played a role in embryo quality. When only live embryos were analyzed, as follicle size and CL volume increased so did the developmental stage of the embryo and quality increased as follicle size increased.