Phosphorus Deficiency Metabolism and Food Utilization in Beef Heifers

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Abstract
Two beef heifers fed a phosphorus-deficient diet containing only 0.13% of phosphorus ceased to grow after 6 months of the low-phosphorus regimen, maintained their body weight during the next year (with 0.09% phosphorus in the food), and finally when fed a diet still lower in phosphorus (with 0.068% phosphorus) lost weight. Two control heifers fed with the same food but supplemented with dicalcium phosphate so that the phosphorus content was above 0.4% increased their weight while their phosphorus-deficient pair mates ceased to grow. The phosphorus-deficient animals developed bone-chewing and coprophagia. The inorganic phosphorus content in their blood dropped from 9.0 to 3.9 mg. of phosphorus per 100 cc. of blood serum while that of the controls remained at the initial level of about 9 mg. phosphorus per 100 cc. of serum. Phosphorus deficiency had no effect on body temperature, digestibility and metabolizability of the food energy, R. Q. and fasting katabolism. Phosphorus deficiency increased slightly the regression of CO2 production and O2 consumption on food intake (not proved with statistical significance). It decreased the partial efficiency of energy utilization, the efficiency of food protein for sparing body protein, and the appetite of the animals. Phosphorus deficiency lowers the total efficiency of energy utilization ( = mean partial efficiency ) mainly by lowering the appetite and secondly by lowering the partial efficiency whereas it does not seem to influence the fasting katabolism.