78 Fertility in lactating dairy cows following timed artificial insemination or timed embryo transfer with fresh or frozen in vitro-produced embryos
A. D. Crowe A B , J. M. Sánchez B C , S. G. Moore A , M. McDonald B , R. Rodrigues D , M. F. Morales D , L. Orsi de Freitas D , F. Randi E , P. Lonergan B and S. T. Butler AA Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland
B School of Agriculture and Food Science, University College Dublin, Dublin, Ireland
C Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Madrid, Spain
D Vytelle LLC, Hermiston, OR, USA
E CEVA Santé Animale, Libourne, Bordeaux, France
Reproduction, Fertility and Development 34(2) 275-275 https://doi.org/10.1071/RDv34n2Ab78
Published: 7 December 2021
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
The aim of this study was to compare pregnancy rates in lactating dairy cows bred by timed AI (TAI) or timed embryo transfer (TET) with fresh or frozen in vitro-produced (IVP) embryos. Oocytes were collected weekly from the ovaries of elite dairy (Holstein Friesian and Jersey; ET-Dairy) donors (n = 40) and elite beef (Angus; ET-Beef) donors (n = 21) using transvaginal ovum pick-up. In addition, oocytes were collected from the ovaries of beef heifers of known pedigree following slaughter at a commercial abattoir (Comm-Beef; n = 119). Following IVM asnd IVF, single grade 1 blastocysts were transferred either fresh or frozen. Recipient cows (all lactating, predominantly Holstein-Friesian) located on 16 herds were blocked based on parity, calving date, and economic breeding index and randomly assigned to receive TAI, ET-Beef, ET-Dairy, or Comm-Beef. A total of 1192 recipients were synchronised with a 10-day progesterone-Ovsynch protocol, of which 240 (20%) were assigned to receive AI (16 h after second GnRH) and 952 (80%) were assigned to receive ET on Day 7. In 12 of the herds, the cows allocated to ET were randomly assigned to either ET-Beef or ET-Dairy, with approximately equal numbers of fresh and frozen embryos transferred. For the other 4 herds, all cows allocated to receive ET were assigned beef embryos (one herd ET-Beef, three herds COMM-BEEF), with approximately equal numbers of fresh and frozen embryos transferred. On the day of scheduled ET, recipient reproductive tracts were examined by transrectal ultrasound, and 91 cows (9.6%) were rejected (no or poor quality CL, luteal cyst, uterine infection). Thus, the final number of recipients included in the analysis was 861. Pregnancy was diagnosed in cows that had not returned to oestrus on Day 32 to 35 and Day 62 to 65 after synchronised ovulation. Data were analysed using generalised linear mixed models including service treatment (AI vs. ET), parity, days in milk, and two-way interactions as fixed effects and herd as a random effect. Overall mean (95% CI) pregnancy/service event at Day 32 was not different (P = 0.96) between AI (47.7%; 41.0, 54.5) and ET (fresh/frozen combined, 47.9%; 44.1, 51.8) and did not differ between dairy and beef embryos (Dairy: 50.1% vs. Beef: 46.1%; P = 0.68). Overall, pregnancy rate was lesser (P = 0.003) on Day 32 following transfer of frozen embryos compared with fresh embryos (Dairy: 40.1% vs. 61.1%; Beef: 41.2% vs. 51.7%, respectively). Across all cows that were diagnosed pregnant on Day 32, pregnancy loss between Day 32 and 62 was greater (P = 0.003) for ET (15.6%) compared with AI (4.7%). There was also an effect (P = 0.001) of embryo type on embryo loss, with greater losses observed for frozen beef (16.6%), fresh beef (17.7%), and frozen dairy (22.8%) compared with fresh dairy (6.7%). In conclusion, pregnancy/service event was similar for TAI and TET, although 9.6% of cows initially synchronised for ET were rejected and of cows that were pregnant on Day 32, pregnancy loss was greater for TET than for TAI.
