PELTIER, T.C.; BARBOZA, P.S.: Growth in the arctic: effects of sex and diet on muskoxen
Muskoxen born in May must grow to survive their first winter from October until plants emerge in May-June. We predicted that growth of lean tissue is affected by dietary N and by sex because adult males are larger than females. Nine muskoxen (Ovibos moschatus; 5:4) were studied from weaning through the second winter (0.5-3y). At 0.8y (March), animals were assigned to low-N (2.1%) or high-N (4.1%) supplements (70g.kg0.75/wk) with ad libitum hay (Bromus sp.; 1.5%N). Sexes grew similarly through 1y. Males grew more than females in autumn (2.5y; 0.29 + 0.06 vs. 0.16 � 0.04 kg/d), but both sexes grew slowly (0.09�0.03 kg/d) in the second winter suggesting that dimorphism is due to late summer growth of males. Body composition was not affected by sex but water (3H2O) space (62 to 94kg) increased more slowly than total mass (79 to 141kg) through the second year (0.8-1.8y) indicating increasing fat content. Subcutaneous rump-fat was greater on the high-N ration (1.33 � 0.15 vs. 1.02 � 0.13 cm) at 1.4y (October) which indicated supplemental protein was deposited as fat. Differences in 15N between the supplements did not affect enrichment of hair or plasma also suggesting poor retention of supplemental N. Diet did not affect limb length, hair density (99mg/cm2) or composition (16%N, 2.9%S). Season affects growth differentially between males and females but supplemental N above 10% crude protein (good quality hay) does not enhance gains of lean tissues. Growth of muskoxen is likely limited by quantity of dietary N and energy especially during late summer when growth rates of lean tissue and hair are greatest. Funding provided by ASTF, UAF, and Alaska EPSCoR.
