The use of embryo transfer to produce pregnancies in repeat-breeding dairy cattle

Abstract Repeat breeding is an important factor affecting economic success in dairy management. The objective of this study was to investigate the effectiveness of transfer of frozen-thawed IVF embryos in establishing pregnancy in repeat-breeding Holstein cattle. Cumulus oocyte complexes were collected by aspiration of 2–5 mm follicles from ovaries obtained at two local abattoirs. After IVF, days 7 and 8 blastocysts were frozen either in 1.5 M ethylene glycol with 0.1 M sucrose, or in 1.4 M glycerol with 0.1 M sucrose. Holstein recipients (122 heifers and 410 cows) included those that had not conceived after 3–21 inseminations. Embryos frozen in ethylene glycol were transferred directly, and embryos frozen in glycerol were transferred after dilution of the cryoprotectant in sucrose into recipients 7 or 8 days after estrus (without-AI group), or following AI (with-AI group). Pregnancy rates were compared by the Chi-square test. Significantly higher pregnancy rates were achieved by embryo transfer following AI (with-AI group) than by embryo transfer alone (without-AI group) in both heifers (49.2 and 29.5%, respectively) and cows (41.5 and 20.4%, respectively; P