KNOTT, K.K.; BARBOZA, P.S.; BLAKE, J.E.; University of Alaska, Fairbanks: Postnatal development of two arctic ruminants

Young reindeer (Rangifer tarandus) and muskoxen (Ovibos moschatus) transition from milk to forage over a short summer at high latitudes. Digestive and metabolic systems must develop quickly to support the dietary transition and establish tissues for winter. We hypothesized that reindeer develop faster than muskoxen. Measures of organs from young reindeer (n = 11 R) and muskoxen (n = 15 M) were compared with adult nonreproductive males of each species (n = 3 R; 5 M). Reindeer were smaller than muskoxen at birth (6.8 vs. 10.1 kg), 30 d (peak milk intake; 17.0 vs. 21.4 kg), and adulthood (115.5 vs. 253.5 kg) but similar at 60 d (27.6 � 5.7 vs. 33.5 � 2.2 kg). Organ mass was adjusted for body size by ANCOVA with ingesta-free mass. Rumen and abomasum were proportionately smaller in young than in adult muskoxen, whereas mass of foregut organs in reindeer was similar between young and adults. Reindeer were born with proportionately large small intestines, liver and kidneys that were similar across age groups. Young reindeer were born with larger thyroid glands than muskoxen and sustained a proportionately large mass of thyroid tissue at 30 and 60d. Absolute thymus mass was also greater in reindeer than in muskoxen at 60d. Precocious development of the foregut could allow young reindeer to switch from milk to forage diets more quickly than young muskoxen. Proportionately larger glands in reindeer than in muskoxen may indicate greater endocrine secretion and immune capacity to support rapid maturation. These changes may facilitate establishment of body protein and fat for the first winter and survival to breeding in the following year.