Factors affecting the outflow of protein supplements from the rumen. 2. The composition and particle size of the basal diet

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Abstract
Two experiments were conducted to investigate the effect of the composition and particle size of the basal diet on the outflow of chromium-treated fish meal from the rumen of lactating British Friesian dairy cows, using Cr-concentrations in faeces. A 4 × 4 Latin square design was used and the cows were fed at twice the estimated energy requirements for maintenance in two equal meals.Fractional outflow rates per h were, 0·079, 0·088, 0·086 and 0·064 for the 1·00 hay: 0·00 concentrate, 0·75 hay: 0·25 concentrate, 0·50 hay: 0·50 concentrate and 0·25 hay: 0·75 concentrate respectively. The difference between 0·75 and 0·50 concentrate was significant (P < 0·05).Grinding of long dried grass through 40 or 20 mm screens had no significant effect on the outflow of Cr-treated fish meal from the rumen, however fine grinding (5 mm) and pelleting significantly reduced the outflow from rumen (P < 0·05). Fractional outflow rates per h were 0·080, 0·086, 0·088 and 0·047 for the long, 40, 20 mm and the 5 mm and pelleted diets respectively.