Content and distribution of macro- and micro-elements in the body of pasture-fed young horses

Objective To determine the content and distribution of Na, K, Ca, P, Mg, S, Cu, Mn, Fe and Zn in the body of pasture-fed young horses and then use a f actorial model to calculate the dietary mineral requirements for growth. Procedure Twenty-one foals were killed at about 150 days of age and the org ans, soft tissues, skin and bones and a sample of muscle were dissected out and weighed. The mineral concentrations of elements in all soft tissues an d bones were measured by inductively coupled emission spectrometry. The tot al mineral element composition associated with a tissue was determined from the weight of tissue and its mineral element concentration. Results Expressed as a percent of total body mineral elements, muscle conta ined 20% Na, 78% K, 32% Mg, 62% Cu, 36% Mn and 57% Zn, bone contained 47% N a, 99% Ca, 81% P, 62% Mg, 30% Mn and 28% Zn while the organs accounted for a smaller percentage ranging from 0.06% for Ca to 26% for Fe. In liver Cu a ccounted for 9.2% of total body Cu. Each kilogram of empty body weight was associated with 1.0 g Na, 2.5 g K, 17.1 g Ca, 10.1 g P, 0.4 g Mg, 1.1 mg Cu , 0.39 mg Mn, 52.5 mg Fe and 21.4 mg Zn. Conclusion The mineral element content of body weight gain is a component u sed in the factorial model to determine dietary mineral element requirement s for growth. The calculated dietary mineral requirements, expressed per kg dry matter, for a 200 kg horse gaining 1.0 kg/day were 1.0 g Na, 2.1 g K, 4.6 g Ca, 3.5 g P, 0.7 g Mg, 4.5 mg Cu and 25 mg Zn.