Before the weaning day (day 23), wild-type pups nursed by acasein deficient dams had a significantly slower growth rate than pups (wild-type and heterozygous) nursed by wild-type dams (p,0.001 for both comparisons). The growth rate of wild-type and heterozygous pups nursed by wild-type dams 1 and 3 was not significantly different (p = 0.729). After weaning, wild-type pups nursed by a-casein deficient dams had a significantly higher growth rate than pups (wild-type and heterozygous) nursed by wild-type dams (p = 0.039 and p = 0.014 respectively). The growth rate of wild-type and heterozygous pups nursed by wild-type dams was not significantly different (p = 0.449) For wild-type pups nursed by a-casein deficient dams the average growth rate was 0.14 g/day for days 1-23 and 0.52 g/day for days 24-60 (cf. Fig. 9b ). For pups (wild-type and heterozygous) nursed by wildtype dams the growth rates were for days 1-23 0.64 g/day and 0.63 g/day, respectively, and for days 24-60 0.47 g/day and 0.45 g/day, respectively (Fig. 10 ).