Short communication: Effects of increased expression of α-lactalbumin in transgenic mice on milk yield and pup growth

Lactose synthase (a complex of β1,4-galactosyltransferase and α-lactalbumin) forms lactose in the Golgi complex of mammary epithelial cells. To determine whether α-lactalbumin is a limiting component in this complex, transgenic mice that expressed bovine α-lactalbumin were studied. Transgenic mice produced 0.5 to 1.5 mg/ml of bovine α-lactalbumin in their milk, 5-to 15-fold more α-lactalbumin than in milk of control mice. Transgenic and control mice produced milk with the same concentrations of lactose, cream, and total solids, and showed similar mammary gland growth, morphology, and histology. Milk from transgenic mice had 0.6% less protein than milk from control mice (P < 0.05). The in vitro lactose synthase activity in mammary gland homogenates from α-lactalbumin transgenic mice was increased (P < 0.05), demonstrating that bovine α-lactalbumin could interact with murine β 1,4-galactosyltransferase. Pups reared by lactating transgenic mice showed a 4% increase in growth on d 10 of lactation, suggesting that milk production was increased (P = 0.06). Milk volume, estimated using the weigh-suckle-weigh technique, tended to be higher (although not significantly) in transgenic mice (P = 0.11). These results suggest that augmenting α-lactalbumin expression in the dam increases the growth of suckling offspring.