Transgenic mice were produced carrying the coding region of the rabbit
κ-casein gene linked to the upstream region of the rabbit whey acidic protein gene.
Mice from the highest-expressing line produced 2·5 mg rabbit κ-casein/ml in their
milk. The foreign protein was associated with the casein micelles and altered micelle
size, though in the high-expressing line rabbit κ-casein also segregated into the whey
fraction obtained after centrifuging the milk samples. Milk from transgenic mice had
the same overall protein content as that from non-transgenic mice, except for the
transgene product. However, litters fed with this transgenic mouse milk grew less
well than litters given milk from non-transgenic mice. This reduction in growth was
not related to changes in mammary gland structure or mammary cell morphology.
Preliminary results indicated that milk from the transgenic mice had a higher
viscosity.