Nitrogen balance studies on pouch young Macropus rufus and M. giganteus (Marsupialia: Macropodidae): The utilisation of cows' milk and carbohydratefree milk replacers.

Abstract

Young Macropus rufus and M. giganteus, aged between 150 and 250 days were reared on two carbohydrate-free milk replacer diets (CF-25 and CF-35 containing, respectively, 25 0Jo and 35% of their total energy as protein). Cows' milk (26% protein energy) was given as a control diet. CF diets were offered to the joeys to provide a wide range of intakes of energy. Cows' milk was offered over a narrow range to avoid diarrhoea. Nitrogen balances over a 5 day collection period demonstrated the protein-sparing effect of the carbohydrate (lactose) in cows ' milk. At the same daily intakes of energy ( 430 kJ kg -0.73) the nitrogen balances of the joeys (mg N kg -0.73) were: CF-25 (n~l4), 195; CF-35 (n ~ l4), 408; cows' milk (n ~ 6), 421; while the daily liveweight changes (g kg -0.73) were: CF- 25, - 0.2; CF-35, +6.6; cows' milk, +11.2. The superior nitrogen balances of joeys given the cows' milk diet could be attributed to the presence of carbohydrate, since similar nitrogen balances could be obtained only with a carbohydrate-free diet if the protein content was raised by some 40% above that in cows' milk. However, the use of cows' milk as the sole feed for pouch young kangaroos is limited by its high content of lactose and the inevitable diarrhoea that follows when cows' milk is fed in amounts sufficient to give acceptable liveweight gains.