In order to distinguish between the effect of the genetic alteration in the offspring and the effect of the modified milk, the mice were put into 3 groups and cross-fostered such that wild-type offspring was nursed by a-casein deficient dams (3 litters with a total of 25 pups; 6 to 11 pups per litter) and heterozygous a-casein [+/2] offspring was nursed by wild-type dams (3 litters with a total of 22 pups; 4 to 10 pups per litter). Wild-type offspring nursed by wild-type dams were used as additional controls (3 litters with a total of 34 pups; 10 to 13 pups per litter; Table 2 ).