Dietary phosphorus as related to clinical and reporductive performance in cattle

During a 10-year period, 96 Hereford females were individually fed diets in which dietary phosphorus (P) ranged from 10 to 35g P/day, 9 to 13g P/day, 6g P/day or less. Symptoms of P deficiency developed within 12 months in animals fed 6g P/day or less. The clinical changes were body weight loss, reduced feed intake, decreased blood and urine P levels, bone depletion, reproductive failure and finally death. Cows showed evidence of recovery within 2 months after receiving 12g or 19g P/day. Thirty-four Holstein cows in their second lactation were individually fed P levels for one year that were 60, 80, or 105R of NRC requirements. Feed intake, body weight, milk production, % protein in milk, and blood and urine P levels were reduced in cows receiving diets containing 60% of NRC requirements. Reproduction was not affected by P levels. Results indicate that 12g of P/day for a 450 kg beef cow, or P equal to 80% of NRC requirements for a 592 kg high-producing dairy cow, are adequate. Phosphorus deficiency seldom occurs in a simple uncomplicated form.