Energy and Carbohydrate Metabolism in Magnesium-deficient Calves

Magnesium participates in almost all phosphorylating enzyme systems of the animal body, and it is to be expected therefore that when animals are deprived of dietary magnesium abnormalities of intermediary energy transfer would result.Indeed, some of the signs of Mg deficiency are similar to those of thiamine deficiency, in which abnormalities of carbohydrate metabolism are known to occur.The present paper is concerned with the total energy exchange and certain aspects of carbohydrate metabolism of calves given rations deficient in Mg.The results show that the elevation of heat production and the abnormalities of carbohydrate metabolism that were observed were not due to failures of enzyme systems in which Mg acts as an activator, but to an increase in muscular activity. EXPERIMENTAL Animals.Ten bull calves were used.Two pairs each consisting of a control (nos.214 and 219) and a Mg-deficient animal (nos.215 and 220) were used in studies of total energy metabolism throughout the whole course of production of the Mgdeficiency syndrome.These involved 108 determinations of the 24 h exchange of energy, water, carbon and nitrogen.One pair was the subject of experiment from September to December 1952, the other from January to April 1953.The experiments with the remaining six calves took place from September to December 1953.Two (nos.225 and 226) were given the control diet, two (nos.221 and 222) the diet deficient in Mg and two (nos.223 and 224) a diet deficient in thiamine, and their carbohydrate metabolism was studied.The general treatment of the calves was as previously described (Blaxter, Rook & MacDonald, 1954). Diets.The normal diet and the Mg-free diet described by Blaxter, Rook & Mac-Donald (1954) were used.The thiamine-free diet was obtained by replacing the commercial casein of the normal diet with vitamin-free casein, by omitting thiamine from the supplement and replacing the liver extract with a supplement of vitamin B,, and folic acid.All calves were given 4 I. daily of the control diet for a short while before the experiment began.Of the experimental diet, 4 1. daily were given, increasing to 6 1. Methods.Energy exchange was determined in a closed-circuit respiration apparatus (Blaxter, Graham & Rook, 1954).Calorific values were determined by bomb calorimetry, carbon by direct combustion and nitrogen by the Kjeldahi procedure.The factors of Blaxter & Rook (1953) were used to estimate fat retention from the carbon and nitrogen balances.9