The digestion of fibre by pigs. 1. The effects of amount and type of fibre on apparent digestibility, nitrogen balance and rate of passage.

The effects of the amount and the type of dietary fibre on the apparent digestibility (AD) by growing pigs of neutral-detergent fibre (NDF) and NDF components, on nitrogen balance and on the rate of passage of digesta were studied using a semi-purified basal diet and fibre in the forms of soya-bean hulls, lupin (Lupinus sp.) hulls, pea (Pisum sativum) hulls, wheat bran, maize hulls, maize cobs, oat hulls and lucerne (Medicago sativa) stems. Both the amount and the type of dietary fibre significantly influenced the AD of dietary dry matter, N and energy. The AD of NDF and of NDF components was markedly affected by the type and the amount of fibre in the diet. The proportion of NDF digested ranged from 0.016 to 0.905, of cellulose from 0.026 to 0.931 and of hemicellulose from 0.010 to 0.999. N retention by the pigs ranged from 12.9 to 25.8 g/d and with some fibres there was a tendency towards increased N retention with increasing intakes of NDF. Rate of passage of digesta, expressed as the 50 and 95% excretion times of stained feed particles, ranged from 22.2 to 85.1 h and 40.0 to 117.1 h respectively. Large individual variations in rate of passage occurred but, in general, the rate of passage tended to increase with increasing intakes of NDF. No strong associations between the rate of passage of digesta and apparent digestibility of NDF components were observed. The results suggest that the extent of fibre digestibility depends predominantly on the origin of the fibre and to a lesser extent on the amount of fibre in the diet.