Comparative Procedures for Measuring the Phosphorus Requirement of Cattle

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Abstract
Eighteen grade Hereford steers averaging 350 lb. initially were used to compare results using various response criteria when three levels of phosphorus were fed. Six animals in each group were fed a low-phosphorus basal diet (0.12%) plus enough supplemental phosphorus to supply each animal with 1.5, 2.0 and 2.5 gm. of phosphorus per 100 lb. body weight, daily. These designated levels of phosphorus were maintained regardless of amount of feed consumed. When response criteria were weight gains, feed consumption, efficiency of feed utilization, percentage digestibility of phosphorus or percentage net retention of phosphorus, 2.0 gm. of phosphorus per 100 lb. body weight did not meet the phosphorus requirement of these animals. When response criteria were bone growth as measured by autoradiographs and plasma inorganic phosphorus level, 2.0 gm. of phosphorus per 100 lb. body weight met the phosphorus requirement. Analyses of selected bones and soft tissues for calcium and phosphorus content revealed no effect of levels of phosphorus. Day-by-day feed consumption records revealed that feed consumption curves in all animals were cyclic in nature and that feed consumption was related to the phosphorus content of the ration. Implications of this observation as related to response criteria and methods of determining the phosphorus requirement of cattle are discussed. Copyright © . .