Effects of embryo transfer in beef cattle on genetic evaluation methodology.

Because female cattle may be superovulated and their embryos dispersed to many surrogate dams, both the recording system and the models for genetic evaluation need to be modified. The recording system must keep track of the breed of the surrogate dams as well as their age and registration numbers. The model for evaluation of beef cattle for traits in which maternal effects are important, for example, must distinguish between natural and surrogate dams. The potential for interactions of breed and age of surrogate dam with sex of calf and the possibility that these may differ from age of natural dam x sex of calf interactions needs further study. A discussion of these issues is given. An example is given to illustrate how surrogate dams might be modeled. Assuming that only the breed of surrogate dam is known and that each surrogate dam gives birth to only one progeny, the mixed model equations for genetic evaluations can be simplified. These are illustrated.