RIS ID
33258
Abstract
Red kangaroos (Macropus rufus) are large (>20 kg) herbivorous marsupials common to arid and semiarid Australia. The population dynamics of red kangaroos are linked with environmental factors, operating largely through juvenile survival. A crucial period is the young-at-foot (YAF) stage, when juveniles have permanently left the mother's pouch but still take milk from a teat in the pouch. Forage quantity and quality have been implicated in drought-related mortalities of juvenile kangaroos. Here we compared how forage quality affected nitrogen (N) intake and excretion by YAF, weaned, and mature, non-lactating female red kangaroos. On high-quality forage ( chopped lucerne hay, Medicago sativa) low in neutral-detergent fiber (43% +/- 1%) and high in N (2.9% +/- 0.1%), YAF and weaned kangaroos had ideal growth rates and retained 460-570 mg dietary N kg(-0.75) d(-1). But on poor-quality forage ( chopped oaten hay, Avena sativa) high in neutral-detergent fiber (64% +/- 1%) and low in N (0.9% +/- 0.1%), YAF and weaned kangaroos could not sustain growth and were in negative N balance at -103 +/- 26 mg and -57 +/- 31 mg N kg(-0.75) d(-1), respectively. Notably, the YAF kangaroos excreted 64% of their truly digestible N intake from forage as nondietary fecal N (NDFN). By weaning age, the situation had improved, but the juveniles still lost 40% of their truly digestible N intake as NDFN compared with only 30% by the mature females. Our findings support field observations that forage quality, and not just quantity, is a major factor affecting the mortality of juvenile red kangaroos during drought.
Included in
Life Sciences Commons, Physical Sciences and Mathematics Commons, Social and Behavioral Sciences Commons
Publication Details
Munn, A. J., Dawson, T. J. & Hume, I. D. (2006). Endogenous nitrogen excretion by red kangaroos (Macropus rufus): Effects of animal age and forage quality. Physiological and Biochemical Zoology, 79 (2), 424-436.