Milk Consumption and Energetics of Growth in Pouch Young of the Tammar Wallaby, Macropus-Eugenii

Abstract

Milk consumption rates of young tammar wallabies, Macropus eugenii, were measured during the first 32 weeks of lactation by means of 22*Na turnover. Milk consumption rates were low during the first 18 weeks or so of lactation, rising from 1.2 to 9.0 ml d-'. Milk consumption rose to 43 ml d-' at 30 weeks post-partum. Changes in milk consumption were paralleled by increases in the size of mammary glands and weight gain by the sucklings. The mass gain for each millilitre of milk consumed (crude growth efficiency) averaged 0.23 g ml-I during the first 26 weeks of lactation, but then increased to more than 0.35 g ml-'. The increased growth efficiency was associated with massive increases in the lipid and energy content of milk from 26 weeks onwards. The conversion efficiencies of milk protein and energy to body materials were intermediate (55-87%, 23-36%, respectively) to those of other mammals, which suggests that the slow growth of pouch young during the first 17 weeks of lactation is the result of restricted milk production by the mother. Milk production and the growth of young were closely correlated with maternal mass (r=0.96; r=0.80, respectively) at 16 weeks post-partum.