Effects of Varying Amounts of Calcium and Phosphorus in Rations for Dairy Cows

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Abstract
Different dietary percentages and ratios of calcium and phosphorus were studied with 48 dairy cows in a randomized block design. The respective members of each block were assigned to one of three ration treatments : a) Ca : P ratio approximately 3:1, 0.4% phosphorus; b) Ca:P 3:1, 0.6% phosphorus; and c) Ca:P 1.5:1, 0.6% phosphorus. Response criteria were blood mineral concentrations, milk yield and composition, parturient paresis, and reproductive performance. Average blood serum inorganic phosphorus was lower (P < .05) in the cows fed the 0.4% phos- phorus ration than in the other treatment groups at all times, except on the day of calving. Blood serum calcium was highest in the group fed the 0.4% phosphorus ration. No differences in blood serum mag- nesium, potassium, copper and zinc, or in milk production and composition were at- tributed to the ration treatments. In the lowest phosphorus group (.4% P), inci- dence of ovarian dysfunctions was higher, and in addition, a larger number of ser- vices per concepgon were required in the second breeding season.