Interval of gonadotropin administration for in vitro embryo production from oocytes collected from Holstein calves between 2 and 6 months of age by repeated laparoscopy

Abstract

Laparoscopic Ovum Pick-Up (LOPU) in calves followed by in vitro embryo production (IVEP) and transfer (ET) into adult recipients has great potential for accelerated genetic gain through shortening of the generation interval. In this study, 11 Holstein calves were subjected to up to six LOPU procedures between the ages of 2-6 months at 2-3 weeks interval. In all cases, the animals received a CIDR 5 days prior to LOPU and were gonadotropin-stimulated starting at 72 h before LOPU using one of three protocols that were rotated twice among the animals during the study. Calves were injected with FSH every 12 h (FSH12h), or every 8 h (FSH8h) or every 8 h until -36 h from LOPU at which point the FSH was replaced with a single dose of 400 IU eCG (FSH8h-eCG). No statistical differences were observed among the 3 treatments in terms of mean follicles available for aspiration (35.7 ± 16 vs. 38.5 ± 25 vs. 31.1 ± 22), mean oocytes recovered (26.5 ± 14 vs. 21.6 ± 10 vs. 19.4 ± 14) and cleavage rate (66.0 ± 14 vs. 61.1 ± 11 vs. 72.2 ± 8), for FSH12h, FSH8h and FSH8h-eCG, respectively. However, FSH8h-eCG resulted in a significantly higher rate of transferable embryos (17.5 ± 8%) compared with FSH12h (8.9 ± 5%, P < 0.05). Oocytes from follicles of ≥5 mm in diameter yielded a higher rate (P < 0.05) of development to the blastocyst stage (13.8%) than those collected from <5 mm follicles (6.8%). Animal age, by comparing animals at <100, 101 to 130 and > 130 days of age, did not affect the mean number of follicles (34.2 ± 15 vs. 39.3 ± 26 vs. 31.6 ± 25), the mean number of oocytes recovered (21.2 ± 10 vs. 24.5 ± 15 vs. 22.6 ± 17), and the cleavage rate (68.6 ± 11 vs. 61.7 ± 12 vs. 70.7 ± 10%), respectively. However, animals in the older age range had significantly higher development to the blastocyst stage (19.9 ± 6 vs. 9.5 ± 8%, P < 0.01) and better embryo quality, as evidenced by higher average cell numbers (119.1 ± 47 vs. 91.5 ± 25, P < 0.05) compared with those in the lower age. Finally, we tested the benefits of relieving endoplasmic reticulum stress by supplementing the culture medium with 50 μM tauroursodeoxycholic acid (TUDCA) and found a numerically higher rate of development to the blastocyst stage (21.1 ± 8 vs. 18.6 ± 4%), but not statistically different, compared with control culture. Overall, our findings indicate that a significant number of transferable embryos (range 10-30) can be produced from Holstein calves before they reach 6 months of age.

Keywords: Dairy cattle; Embryo development; FSH; Laparoscopic ovum pick-up; Prepubertal.