Changes in the milk proteins during lactation in the tammar wallaby, Macropus eugenii

Samples of whey proteins from the milk of tammar wallabies, Macropus eugenii, were examined by acrylamide gel electrophoresis at all stages of lactation up to 280 days post partum. Whey albumin, beta-globulin and gamma-globulin fractions had similar electrophoretic mobility to that of the equivalent serum protein fractions, but the proteins in the alpha-globulin and pre-albumin regions differed markedly. The alpha-globulins are presumed polymorphic because individuals at the same stage of lactation showed great variability in these electrophoretic regions: up to five polymorphic bands were recognized. Milk proteins changed qualitatively throughout lactation, and in particular the concentration of the pre-albumin and alpha-globulin fractions increased from approximately day 180 to the end of lactation. Total protein concentration of both whole milk and whey approximately doubled in the second half of lactation compared to the first half, reaching maximum mean values of 114 +/- 47 and 96 +/- 50 gl-1, respectively. Whole milk contained consistently more protein than whey, presumably due to the casein it contains.