The potential for genetic change in milk fat composition.

Effecting genetic improvement requires genetic variation, a mechanism of selection, and an economic incentive for the improvement. Limited data suggest that there is within-breed genetic variation in milk fat composition, but accurate estimates are lacking. There is some evidence for modest differences among breeds. Substantial differences exist among species, indicating that substantial genetic change in fat composition is biologically possible. The economic incentives for genetic change are not clear. Changes in fat composition that would improve the quality of one milk product would often be detrimental to other products. Such changes would best work where subpopulations produced milk for specific end products. Such division of the industry would be difficult to organize and might impede existing improvement programs. Changes in fat composition that increased consumer acceptance of milk products, such as reduced saturated fat concentration, might increase the market for milk products. However, only large changes in composition are likely to affect consumer acceptance; thus, the gradual changes of conventional genetic improvement would produce little or no return to the breeder. Genetic changes that reduced processing costs or increased product value might have low to moderate economic value, inducing slow rates of change. Production of transgenic animals might provide a route for genetic alteration of fat composition in the future. Such improvement would most likely be cost effective in a subdivided production industry in which milk from cows of a particular genotype can be directed to a particular milk product. It is concluded that although alteration of fat composition could be achieved, it is unlikely to be an important component of genetic improvement of dairy cattle.