potentially be bypassed through the use of in vitro embryo transfer. The use of oocytes collected

from abbatoir-derived ovaries can be used as an inexpensive source of genetic material for

producing embryos for large scale embryo transfer breeding schemes. While there are producer

concerns about the genetic make-up of abbatoir-derived oocytes, a study by Rutledge (1997)

indicates that the genetic merit of cows sent to slaughter is only slightly lower than for the

average cow in the herd of origin. Moreover, the ability to produce hundreds of embryos with

only a few straws of semen allows for genetic improvement by utilizing semen from genetically

valuable sires that in other instances, would be too expensive. To date, few studies have directly

compared the pregnancy rates obtained with artificial insemination versus embryo transfer in

lactating dairy cattle (Putney et al., 1989; Ambrose et al., 1999; Drost et al., 1999; Al-Katanani et

al., 2002). The use of embryo transfer in situations where pregnancy rates to artificial

insemination are above average does not seem to provide any increase in fertility (Sartori et al.,

2006). In contrast, however, in cases where pregnancy rates to artificial insemination are low,

such as during heat stress, in vitro embryo transfer can be effective in improving fertility in

lactating dairy cows (Ambrose et al., 1999; Al-Katanani et al., 2002).

Optimize Breeding Schemes

 Production of embryos in vitro also has potential for enhancing crossbreeding schemes.

The use of crossbreeding to take advantage of heterosis is commonly used in beef production

systems. While seldom used for dairy cattle production in the United States, crossbreeding has

received renewed attention recently (McAllister, 2002; Heins et al., 2006a; Heins et al., 2006b).

Production ofF1 crossbred embryos in vitro for transfer to Fi recipients could improve

crossbreeding schemes by eliminating the loss of heterosis and increased phenotypic variation

that occurs when Fi females are mated to purebred or crossbred sires (Rutledge, 2004).