Straw in Different Proportions as Sole Roughage in Diets for Cows in Mid-lactation

Abstract

A complete switch-back trial was designed for 12 cows in mid-lactation; they received three different rations of chopped wheat straw (Triticum aestivmn) and concentrates -45:55 (A), 30:70 (B), and 15:85% (C). Milk yield and composition in all three treatments were similar; milk fat was relatively low although the molar percentage of ruminal acetic acid was high in all groups. Concentration of plasma glucose was similar in all three groups whereas plasma free fatty acids of group B were higher than for the two others. Differences in the composition of plasma free fatty acids were not significant. Digestibility of dry matter decreased slighly with increasing percentage of straw in the ration; metabolizable energy per gram dry matter was equal in rations B and C and lower in ration A. Cows in group C showed a higher gross efllciency in using metabo-]izable energy for milk production.