Effects of Various Hay: Concentrate Ratios on Nutrient Utilization and Production Responses of Dairy Cows. II. Observations on Ration Digestibility and on the Excretion Pattern of Chromic Oxide

Abstract

A digestibility study made with the chromic oxide ratio technique was conducted with 36 dairy cows. Four ratios of hay to concentrates (replacement on an estimated net energy basis), 3 feeding levels, and 3 ability levels were used. The nature of the fecal excretion pattern of chromic oxide, under the wide range of conditions imposed by the experimental design, also was studied. From the high to the low hay rations, the dry matter digestibilities were, respectively, 54.5, 58.5, 55.2, and 63.1%. Dry matter digestibilities for high, medium, and low ability cows, and for high, medium, and low feeding levels were essentially unchanged. The fecal excretion of chromic oxide followed a diurnal pattern. Maximum excretion of chromic oxide occurred in samples taken at 5 A.M. or 9 A.M. and the minimum excretion in samples at 5 P.M. or 9 P.M. This diurnal excretion pattern was largely independent of the wide variation in the physical nature of the rations and of the feeding level.