Comparisons of methods for estimating in vivo digestibility of feedstuffs in dairy cattle

Abstract

An experiment was done which compared the digestion coefficients obtained from dairy cows using the traditional separate total collection of faeces and urine with a modification of the combined collection technique described by Lindgren (1981). The use of the dry matter contents of the various components of excreta to obtain faecal output was examined. Four cows were used in two cross-over trials, one in which pasture was fed, and the other where maize silage and lucerne hay constituted the diet. Combined collection of excreta gave accurate measures of digestion, particularly with wet feeds where urine formed a large proportion of the total excreta voided. With the dry feeds, greater attention needed to be paid to mixing although there may also have been problems with losses of volatile compounds from mixed excreta. If the combined collection technique is to be used, it should only be considered if a full 24 h separate collection of faeces and urine is included because wide diurnal variation was found in most faecal components. Milk production was higher with combined collections than with separate collections (18.2 vs. 17.3 kg day −1) which suggests that combined collection, without urine separators, was less stressful to the animals.