1. The use of a nylon-bag technique for pig feed digestibility determination was studied. Bags, measuring 25 × 40 mm and containing feed samples, were introduced into the pig gastrointestinal tract through a duodenal cannula, and recovered in the faeces between 23 and 69 h later. The disappearance of organic matter and crude protein (nitrogen × 6.25) from the bags was compared with in vivo apparent digestibility, determined by conventional faecal-collection methods, and neutral-detergent-fibre content for eleven feeds. The residues left in the bags after passage through the intestine from whole-crop-pea (Pisum sativum) and barley-grain samples were analysed for starch, non-starch polysaccharide residues, Klason lignin, crude protein and ash.
2. Dry matter disappearance of barley or whole-crop peas was not influenced by increasing bag pore size from 10 to 36 μm or sample weight from 250 to 1000 mg. Pepsin (EC 22.214.171.124) pretreatment had no effect on the degradation in the bags of the feeds investigated.
3. Organic matter and crude protein disappearance from the bags exceeded in vivo apparent digestibility by up to 0.10 and 0.42 units respectively. In vivo apparent organic matter digestibility could be predicted (P < 0.001) by the organic matter disappearance from the bags and the neutral-detergent-fibre content of the feed, while in vivo apparent crude protein digestibility was highly correlated (P < 0.001) to all these indices but poorly to crude protein disappearance from the bags.
4. Klason lignin was the least degraded component measured in the whole-crop-pea and barley residues from the bags, while starch was completely digested. Of the non-starch polysaccharide residues, xylose was the most resistant to degradation in both samples whereas other sugars vaned in susceptibility to solubilization between samples.
5. Results are discussed in relation to the potential uses of the nylon-bag technique described in the present paper for studies in simple-stomached animals.