Calcium metabolism in red deer (Cervus elaphus) offered herbages during antlerogenesis: kinetic and stable balance studies

Summary Kinetic studies of Ca metabolism, using 45 CaCl 32 , were carried out on two mature red deer stags during the period of maximum rate of Ca deposition in the antlers. They were offered green-feed oats to provide energy for maintenance; the diet provided approximately 42mg Ca/kg W per day. Ca appeared to be irreversibly lost from the circulation into the antlers and could be treated for kinetic purposes in the same way as loss of Ca from the body in milk. The size of the rapidly exchangeable Ca pool in the body, excluding the antlers, was 0·21 g/kg W, similar to estimates for lactating cattle. Rates of Ca deposition in the antlers of the two stags, calculated from the model of Ca metabolism, were 58·4 and 38·6 mg Ca/kg W per day. Net endogenous loss was 6–7 mg Ca/kg W per day, much lower than estimates available for other ruminant species. Only 25–40% of Ca requirement or 11–24 mg Ca/kg W per day was derived from the diet, suggesting that the availability of Ca in greenfeed oats is much lower than current estimates for forages. Bones removed on completion of the experiment showed evidence of considerable skeletal demineralization. In other stags subjected to stable Ca balances at the same stage of antler growth, while consuming ryegrass-white clover forage, 60–80% of Ca requirement was derived from the diet, with calculated rates of true absorption of 32–46 mg Ca/kg W per day. These rates of Ca absorption are low compared with values observed in other ruminants at times of high Ca demand such as during lactation.