A Study of the Phosphorus Requirement of Dairy Cattle: I. Phosphorus Requirement for Growth and Reproduction from Three Months of Age to First Calving

Abstract

Summary (1)This experiment was designed to determine the phosphorus requirement of dairy cattle when a ration of alfalfa hay with less than 0.2 percent phosphorus, corn silage, and corn was fed. (2)The low phosphorus ration caused an immediate lowering of the inorganic blood phosphorus.These values remained lower than normal during the first eighteen months of age. (3)The blood calcium values were highest during the time that the phosphorus values were lowest. The calcium values were slightly higher than the normal values during the first 18 months of age but were still within normal range. (4)Other symptoms of phosphorus deficiency exhibited by the heifers in lot I (low phosphorus ration) were depraved appetite and a reduced appetite for hay and silage. (5)The ration fed' the heifers in lot I which contained from 5.7 to 9.9 grams of phosphorus per day from three to 18 months of age was insufficient when the calcium-phosphorus ratio was from 4:1 to 5:1 and when the sources of vitamin D were five pounds of sun-cured alfalfa hay and sunshine. (6)Ten and three tenths grams of phosphorus per day appeared to furnish sufficient phosphorus for the heifers in lot II fed the basal ration supplemented with bone meal from three to six months of age. (7)Ten to 12 grams of phosphorus daily furnished sufficient phosphorus for normal growth, maintenance, and for the development of the fetus from 18 months of age to first calving as indicated by blood phosphorus and the strength and size of calves at birth. (8)During gestation the blood calcium and phosphorus values were normal for both groups. The blood phosphorus values of both groups decreased markedly immediately prior to parturition. (9)The phosphorus requirement for growth is not directly proportional to body weight but probably depends on the rate of growth. Consequently, the method used in this experiment of feeding about 0.2 per cent of the dry matter as a low phosphorus ration to the animals in lot I and 0.41 per cent phosphorus as optimum phosphorus level to those in lot II is not a satisfactory method of studying phosphorus requirement for growth. However, under practical farm conditions in which alfalfa hay and the cereal grains furnish protein and energy, calves consume more food as they grow older even though the rate of growth declines.