Seasonal changes in the composition and mineral content of the body of hill ewes

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Abstract
SUMMARY: Groups of ewes kept under hill conditions were killed at intervals during October to July 1965–66. Supplementary feed was given between February and May. The carcasses were divided into soft tissue, uterus and its contents and skeletal fractions. Each fraction was dissolved in HNO3 and its fat and mineral content measured. The sheep were heavier in November and lighter in May during lactation than at other times. The content of fat in the body fell progressively from October to May and then increased; initially fat was withdrawn only from the soft tissues but by April and May the fat contents of both skeleton and soft tissues were exceedingly low. The weight of fatfree soft tissue remained relatively constant but was heaviest in July. Fat-free skeleton fraction was lighter in January than in April.The contents of the predominantly intracellular ions, P, Mg and K in the soft tissue fell between November and January, remained constant between January and May and then increased. There was an increase in Na towards the end of pregnancy followed by a marked fall after parturition. The contents of Ca and P in the skeleton fell between November and January and during lactation between April and July. There was a marked increase between February and April when supplementary feeding was given. Evidence that Mg was selectively removed from the skeleton was obtained in November and January, two sheep having Ca:Mg ratios in skeleton greater than 100. Na and K contents of the skeleton were greatest at the end of pregnancy in April. For the lambs between 6 and 23 kg live weight, each kg of live-weight gain contained 8·8 g Ca, 5·0 g P, 0·27 g Mg, 0·83 g Na and 1·85 g K.