Embryo transfer as a reproductive management tool

Abstract

Regardless of whether generated by superovulation (otherwise called multiple ovulation – embryo transfer; MOET) or by in vitro production (IVP), the most common purpose of transfer of cattle embryos today is for genetic improvement. The advent of genomics means that genetically-superior females can be identified with acceptable accuracy and these females can be used to produce up to 100 or more embryos from a cow or heifer each year. Embryo transfer can also be used to rapidly establish a herd of high-producing animals, as exemplified by the large numbers of embryos exported from North America to other countries to establish high-yielding dairy herds. Production of embryos in vitro is also an effective means of utilizing sexed semen because one straw of sexed semen can be used to produce multiple embryos in vitro. The pregnancy rates following transfer into recipients is similar between cows receiving embryos produced sexed semen and those receiving embryos produced with conventional semen (Xu et al., 2006; Rasmussen et al., 2012). A less well appreciated use of the bovine embryo is as a tool for improving pregnancy rates. In general, the percent of cows pregnant after receiving an embryo is not appreciably higher than pregnancy success following artificial insemination (AI). However, embryo transfer can improve fertility of cow populations when reproduction is suboptimal because of heat stress. There is also some evidence in dairy cattle that embryo transfer can improve pregnancy rates of lactating cows classified as repeat breeders.