Tritiated Water in the Measurement of Milk Intake and Tissue Growth of Ruminants in the Field

Abstract

MEASUREMENT of the turnover and content of water in grazing animals is a useful approach to their physiological ecology. Young ruminants obtain this water from milk. Linnaeus, when he named the mammals, recognized that the provision of milk is a major adaptation of these vertebrates to dry land, but it is not easy to measure the amount of milk taken by mammalian young in the field¹. The supply of milk, however, determines not only the early growth but often the survival of neonates³. Most milk is more than 80 per cent water and the burning of hydrogen in the milk solids yields a volume of water near to that of the solids themselves, so that measurement of water turnover in the young provides a close estimate of milk intake⁴. The use of tritiated water in the young allows estimation of the body solids content as well as an integrated measure of milk taken, while mother and offspring live undisturbed (apart from recapture at 7–10 day intervals) in their normal environment.