Potential of Cytoplasmic Effects for Selection in Dairy Cattle

Maternal cytoplasmic inheritance may cause an upward bias in heritabili ty estimates from daughter on dam regression. Inaccurate evaluations of bulls or dams of future sires would result if such estimates were used in genetic evaluation. Expected genetic selection differential for bulls would be overestimated, but genetic gain would be little affected by incorrect heritabili ty estimates. Genetic evaluations of dams of sires would be less accurate when incorrect heritabili ty estimates are used, but actual selection differentials would be only slightly less than opt imum. If cytoplasmic effects were ignored during selection, less genetic improvement would seem to be the result. However, expected genetic gain would be only slightly increased if selection considered both nuclear and cytoplasmic components of inheritance rather than nuclear inheritance only. Reasons for both results are that selection for cytoplasmic effects can be done directly only through dams of cows for which selection is not very intense and that overestimates of heritabili ty have little effect on genetic selection differentials as compared to using correct estimates of heritabili ty. Expected genetic gain, if based on overestimates of heritabili ty, however, will be considerably greater than can be realized.