Nutrition of grazing cattle. 3. Estimation of protein, phosphorus and calcium in mixed diets

Abstract

Regressions developed to relate dietary and faecal composition in terms of protein, phosphorus and calcium are applied to estimate the percentages of protein, phosphorus and calcium in diets comprising two or more feeds differing widely in chemical composition. The regressions for phosphorus and calcium give satisfactory results when applied over a wide range of dietary phosphorus and calcium levels in a variety of feedstuffs. The regression for estimating protein percentage is unsatisfactory, giving a marked under-estimate of the protein level in most mixed diets. When the diet consists of two feeds which differ in phosphorus or calcium content, analysis of each feed together with the regression estimates of phosphorus and calcium permits an assessment of the relative proportion of each feed in the diet. From this proportion the protein content in the mixed diet may be calculated.