Body composition of muskoxen (Ovibos moschatus) and its estimation from condition index and mass measurements

Abstract

We used data on the anatomical and chemical body composition of 22 muskoxen (7 adult females, 6 subadult females, 2 yearlings, 5 calves, and 2 near-term fetuses) from Victoria Island, Northwest Territories, to evaluate basic patterns of body composition and allometric growth in this species and to assess methods of estimating body composition from mass and index measurements. Ingesta-free body mass (IFBM) ranged from 9 kg in the 2 fetuses to 150 kg in the largest cow, and fatness from 2.0% of IFBM in a newborn calf to 29.0% in a mature cow. The proportion of fat increased most rapidly in muskoxen with IFBM ≥ 100 kg. In the fatter females, about 33% of the fat was intermuscular, 27% subcutaneous, 20% abdominal, and 13% intramuscular. In muskoxen ≥ 3 years old, ingesta accounted for 26.8 ± 1.1% of body mass and pelage for 4–4.5% of IFBM. Muscle mass was best estimated from masses of individual muscles, protein mass from IFBM, bone mass from the masses of limb bones, and ash mass from IFBM. Dissectible and total fat masses were less predictable, and were best estimated by multiple regressions combining kidney fat mass and a measure of body mass with up to three other measurements. Body composition and fat distribution in muskoxen were similar to those in cattle and sheep and the extent of fattening exceeded that reported in wild ruminants except for Svalbard reindeer (Rangifer tarandus platyrhynchus).