In order to assess whether the deficient nutrition during lactation has an impact on general development, mice in the three experimental groups were exposed to an early phenotyping protocol including an adapted version of the general screen of the SHIRPA assay [22] . Pre-weaning observations indicated physical impairment in the 'small' mice. Measures of maturation (e.g. eye opening; tables 3 and 7) occur with a slight delay with respect to control animals. 60% and 50% of the pups nursed by wild-type dams had both eyes opened on day 14, all of the pups nursed by acasein deficient females still had their eyes closed at that age, opening them only around 3 days later (Table 7) . Physical abilities which rely on physical strength and coordination when tested on day 21 are significantly less developed in pups reared by a-casein deficient dams (Table 8 ). Significantly fewer of the growth impaired animals (36%, P-value,0.001 Fisher's exact test) were able to hold on to the pole in the vertical pole test, whereas none of the pups nursed by wild-type dams fell off before the pole reached a vertical position. Some animals nursed by a-casein deficient dams presented a rough condition of the fur (84%, P-value,0.001 Fisher's exact test) whereas all control animals had normal fur condition. Grip strength in growth impaired pups was significantly lower (P = 0.001), as 36% of the animals could not hold on to the cage lid for 15 seconds when it was turned upside down, compared to 3% and 0% in the two control groups. Animals nursed by knockout females defecated less during handling and scoring on day 21 (P-value,0.001, Mann Whitney U). Also significantly fewer (76%, P = 0.004) pups nursed by a-casein deficient females showed a provoked biting response at day 21 when compared to pups nursed by wild-type dams (100%). In summary, at preweaning the a-casein deficient milk suckled pups were smaller and physically weaker than those reared on wild-type milk.