The evaluation of cattle foods and diets in terms of the ruminal concentration of volatile fatty acids I. The effects of level of intake, frequency of feeding, the ratio of hay to concentrates in the diet, and of supplementary feeds

Abstract

1. A study was made of the effects of feeding regimen and the composition of the diet on the ruminal production ofV.f.a.'S in cattle.2. The day-to-day variations in the pattern of rumen fermentation in cows given a diet of hay and concentrates indicated that within-cow differences in the molar proportions of the acids from diet to diet are of significance if they exceed about 3% (of the mean value) for acetic acid, about 10% for propionic and butyric acids, and about 25% for valeric acid. The results emphasized also the important differences to be found between cows given the same diet.3. A change in the frequency of feeding from once to four times daily at a constant daily drymatter intake had little effect on the daily mean values for pH, concentration of totalV.f.a.'S, or the molar percentages of the individual acids, but almost invariably decreased the range of values observed between feeding.4. With diets of hay and of hay and concentrates an increase in daily dry-matter intake was associated with a fall in pH and an increase in the concentration of totalV.f.a.'S; with the diet of hay and concentrates there was a considerable decrease in the molar percentage of acetic acid and a corresponding increase inN-butyric, but there was little change in the molar percentages of the acids with the diet of hay.