Published online by Cambridge University Press: 02 September 2010
Processing roughages generally causes marked changes in the particle size of the feed and this review is restricted to the effect of this on nutritive value; processing roughages by chemical methods is not considered. Where possible experiments with milking cows given processed artificially dried forages are discussed, but unfortunately relatively little work has so far been reported with these feeds. It is therefore necessary to refer to results from a much larger body of American information on processing field-cured lucerne, and to the few European studies with milled hays and straws. Much of the work has been done with small numbers of cows and often without reporting the particle size of the processed roughages. On the occasions this information was given it shows that, between experiments, the average particle size of pelleted hay varied enormously from 1·35 mm to 0·22 mm. The average particle size of the feed was the size of mesh through which half the total weight of particles passed (Gill, Campling and Westgarth, 1966). Processing a feed into pellets therefore does not imply a common particle size.