Abstract #T317

# T317
In vitro fertilization (IVF) from low or high antral follicle count pubertal beef heifers using semi-defined culture conditions.
C. C. Chase*1, R. A. Cushman1, A. K. McNeel1, E. C. Wright-Johnson1, O. L. Amundson2, E. L. Larimore2, B. N. Richardson2, G. A. Perry2, S. C. Tenley3, J. R. Wood3, A. S. Cupp3, J. L. Vallet1, D. D. Sypherd1, J. L. Miles1, 1USDA, ARS, US Meat Animal Research Center, Clay Center, NE, 2Dept. of Animal Science, South Dakota State Univ, Brookings, SD, 3Dept. of Animal Science, University of Nebraska, Lincoln, Lincoln, NE.

Our objective was to compare the in vitro maturation and fertilization of oocytes collected from low and high antral follicle count (AFC) heifers. Trans rectal ultrasonography was performed on 120 heifers to determine AFC and presence of a corpus luteum (i.e., pubertal). Those 10 heifers with the lowest AFC (avg. 14.2) and those 10 heifers with the highest AFC (avg. 29.9) all with evidence of estrous cyclicity (i.e., pubertal) were synchronized with 2 injections of PGF and killed over 4 d; on d 5 to 6 of the estrous cycle. Nineteen heifers (n = 9 low and n = 10 high AFC) were at the appropriate stage of the estrous cycle. The IVF procedures and media were as described (P. J. Hansen’s Laboratory, IVP Protocol). Cumulus-oocyte complexes (COCs) from follicles less than 8 mm in diameter were cultured in maturation medium (5% CO2; 38.5°C) for 24 h. Matured COCs were fertilized using thawed frozen semen from a crossbred bull that was purified using Percoll separation procedures. Motile spermatozoa were added to COCs in fertilization medium at a final concentration of 1x106 spermatozoa per mL. About 24 h later, presumptive zygotes were placed in micro drops of development medium under oil, and cultured (5% CO2; 5% O2; 38.5°C). On d 3 and 8 after fertilization, cleavage and blastocyst development, respectively, were assessed. Data were analyzed using the MIXED procedure of SAS and the model included the effects of collection d, group, and their interaction. Percentage data were analyzed using the GLIMMIX procedure with a binomial distribution and a logit link. Neither collection d nor the interaction differed (P ≥ 0.13). High compared with low AFC heifers had greater numbers of COCs (P < 0.01; 27.0 ± 3.79 vs. 9.6 ± 3.97 per heifer), oocytes that cleaved (P < 0.04; 15.2 ± 2.63 vs. 6.1 ± 2.76 per heifer), and developed to blastocysts (P < 0.007; 4.08 ± 0.662 vs. 0.83 ± 0.695 per heifer). There was no difference (P > 0.9) in the percentage of COCs that cleaved (low = 52.3 ± 8.37%, high = 53.6 ± 7.98%) or in the percentage of COCs that developed to blastocysts (P < 0.13; low = 6.6 ± 2.79% vs. high = 13.7 ± 2.66). These results agree with our previous findings, high AFC heifers had greater numbers of COCs, oocytes that cleaved, and blastocysts compared with low AFC heifers; however, AFC does not appear to affect oocyte development and maturation through the blastocyst stage.

Key Words: heifer, IVF, antral follicle count