| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2004 Young ruminants must grow and develop digestive function during brief summers in the Arctic. I examined growth and development of nutritional organs in reindeer and muskoxen as neonates (1 d), during transition from milk to forage (30-60 d) and at maturity. Reindeer and muskoxen gave birth to relatively smaller offspring than ruminants from more temperate regions. Costs of small birth mass are likely offset in neonates by an increase of thyroid hormones to enhance thermogenesis and hepatic reserves that provide additional nutrients during early development. Body mass gains during the neonatal period (1-30 d) were associated with well-developed abomasa that allow young to utilize milk immediately after birth. Transition to forage coincided with mass gains of the rumen, small intestine and colon. Digestive morphology also was modified to facilitate fermentation of plants and enhance digestion and absorption of nutrients by 60 days of age. Digestive anatomy of young reindeer and muskoxen also indicated that feeding strategies of adults may be determined from birth. Growth of reindeer and muskoxen, therefore, is dependent upon an endogenous sequence of nutritional development that allow young to take advantage of concentrated milk after birth and time fermentative function to plant emergence at high latitudes. These advances permit young to meet requirements of growth and establish reserves before winter. Introduction -- Growth in Arctic ungulates: postnatal development and organ maturation in Rangifer tarandus and Ovibos moschatus -- Nutritional development of feeding strategies in Arctic ruminants : digestive morphometry of reindeer, Rangifer tarandus, and muskoxen, Ovibos moschatus -- Conclusion.
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