Effect of rabbit kappa-casein expression on the properties of milk from transgenic mice

Transgenic mice were produced carrying the coding region of the rabbit kapp a -casein gene linked to the upstream region of the rabbit whey acidic prot ein gene. Mice from the highest-expressing line produced 2.5 mg rabbit kapp a -casein/ml in their milk. The foreign protein was associated with the cas ein micelles and altered micelle size, though in the high-expressing line r abbit kappa -casein also segregated into the whey fraction obtained after c entrifuging the milk samples. Milk from transgenic mice had the same overal l protein content as that from non-transgenic mice, except for the transgen ic product. However, litters fed with this transgenic mouse milk grew less well than litters given milk from non-transgenic mice. This reduction in gr owth was not related to changes in mammary gland structure or mammary cell morphology. Preliminary results indicated that milk from the transgenic mic e had a higher viscosity.