Growth in an Arctic grazer: Effects of sex and dietary nitrogen on yearling muskoxen
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abstract
Muskoxen (Ovibos moschatus) are sexually dimorphic ruminants from a highly seasonal environment. Five males and 4 females were assigned at the start of spring (309 days) to supplemental diets of either 12.8% or 25.1% protein with ad libitum grass hay (9.1% protein). Males grew more rapidly than females especially in the 2nd autumn (0.29 versus 0.15 kg/day) but returned to slow growth in the next winter (0.09 kg/day). Water space (3H 2O) grew from 62 to 94 kg, whereas fat increased from 1.36% to 16. 52% of body mass from 312 to 522 days of age. Depth of subcutaneous fat was greater on the high nitrogen (N) supplement, which indicated deposition of excess dietary protein as lipid. Differences in protein content and 15N enrichment of the supplements did not affect density, composition, or enrichment of hair, which indicated minimal incorporation of supplemental protein into lean mass and a low requirement of N for growth. Low body fat may impair survival of muskoxen during the 1st winter, whereas gains of mass as fat and lean tissue in the 2nd summer may be influenced by diversity and abundance of forage and by differential maturation of males and females.
