120 Juvenile in vitro fertilization embryo transfer in seasonal pasture-based dairy systems

Laparoscopic ovum pickup (LOPU) in prepubertal calves followed by in vitro embryo production and transfer into adult recipients, also known as juvenile IVF embryo transfer (JIVET), has great potential for accelerated genetic gain through significant shortening of the generation interval. The objective of this study was to investigate the use of JIVET in a seasonal pasture-based dairy production system. Elite Holstein Friesian (HF) donor calves (n = 49) from seven herds were enrolled, all of which were within the top 2% of the Economic Breeding Index (the dairy genetic index used in Ireland). On the day of LOPU, mean (±SD) calf age was 79.6 ± 9.9 days (range: 55–102). Calves were derived from either embryo transfer (n = 21) or AI (n = 28). Immature cumulus–oocyte complexes (COCs) were collected from each donor calf on one occasion following stimulation with FSH using a proprietary protocol. After IVM, IVF was conducted using X-sorted semen from a panel of eight HF bulls (both at 38.5°C, 5% CO₂ in air). After 7 days of in vitro culture (38.5°C, 5% CO₂, 5% O₂, 90% N₂), a single blastocyst (grade 1, n = 40; grade 2, n = 34; grade 3, n = 13) was transferred fresh to the uterine horn ipsilateral to the corpus luteum (CL) in recipients (n = 87) synchronized using a Progesterone-Ovsynch protocol (heifers, n = 77; lactating dairy cows, n = 10) located in four herds. On the day of scheduled embryo transfer, 7 days after presumptive estrus, recipient reproductive tracts were examined by transrectal ultrasound to confirm the presence of an adequately sized CL. Pregnancy diagnosis was carried out on Day 35 by transrectal ultrasonography and pregnant recipients were re-examined on Day 62–64. Embryonic loss was characterized as loss between Day 35 and Day 62–64. LOPU data were analyzed using univariate and descriptive statistics procedures in SAS. The mean (±SD) number of COCs recovered per donor was 14.9 ± 15.4 (range, 1–71), and the mean number of transferable embryos produced per donor was 1.77 ± 2.9 (range, 0–15). Calf origin (ET vs. AI) did not affect total oocytes recovered (14.9 vs. 15.0; P = 0.99) or total number of transferable embryos produced (1.3 vs. 2.1; P = 0.36) per donor. Mean cleavage and blastocyst rates following IVF were 65.0 ± 26.7% and 12.8 ± 18.6%, respectively. Across all embryos transferred, pregnancy/ET on Day 35 was 39.1% (34/87) and 33.3% (29/87) on Day 62–64. The pregnancy/ET for grade 1, grade 2, and grade 3 embryos on Day 35 was 47.5% (19/40), 38.2% (13/34), and 15.4% (2/13), respectively, and the corresponding values on Days 62–64 were 45% (18/40), 29.4% (10/34), and 7.7% (1/13), respectively. Embryonic loss between Day 35 and Day 62–64 was 5.7%. The results of this pilot study confirm the feasibility of using JIVET in seasonal pasture-based dairy production systems.

This study was supported by the Department of Agriculture, Food and the Marine Research Stimulus Fund (Grant 2021R665) and Trans Ova Genetics.