1. Maize, wheat and barley meals, and a protein-free diet were each force-fed to 24 intact and 24 caecectomised adult cockerels. For each test, birds were starved of solid food for 48 h, fed, and then excreta collected for 48 h. 2. Quantities of nitrogen (N) and amino acids excreted after feeding the protein-free diet did not differ between intact and caecectomised birds. 3. True digestibility coefficients of N and amino acids did not differ between intact and caecectomised birds. 4. Differences between cereals in apparent digestibility of amino acids were inconsistent and more readily attributed to differences between amino acid intake than bioavailability. 5. Differences between cereals in true digestibility of amino acids were confined to higher values for N, aspartic acid, alanine and leucine in maize than in barley or wheat meals.

1. Three isonitrogenous diets were formulated in which soyabean (dehulled), sunflower (hulled) and groundnut (dehulled) meals were the sole protein sources. 2. 50 g of each diet was tube-fed to each of 24 intact and 24 caecectomised cockerels, which had been previously starved for 48 h. Excreta were collected, individually, for 48 h. The concentrations of amino acids in the diets and excreta were determined, and digestibility coefficients calculated. 3. Differences between intact and caecectomised birds for true digestibility evaluations reached significance for threonine, glycine and lysine only. Deamination of threonine and glycine, and synthesis of lysine, in the caeca was implied. 4. Neither the true digestibility of nitrogen, nor that of the sum of the amino acids differed between protein sources. 5. True digestibilities of most essential amino acids, considered individually, in sunflower and groundnut meals were similar to or greater than, those of soyabean meal. Exceptionally, lysine was more digestible in soyabean (0.879) than in sunflower (0.722) or groundnut (0.788) meals.

Evaluation was made of the extent to which amino acids in maize, wheat and barley meals were digested by pigs.Apparent Digestibility (AD) of an individual amino acid was determined as the difference between amino acid intake and amino acid in the ileal digesta, expressed as a percentage of the intake. AD was adjusted to True Digestibility (TD) by correcting for the endogenous amino acid in the digesta, measured after feeding protein-free diets. An attempt was made to account for the possible influence of dietary fibre on digestility determinations by using protein-free diets which provided similar intakes of crude fibre as that achieved with the cereals.4 littermate male pigs (22 kg live weight) were each surgically modified to create an ileo-rectal anastomosis. The large intestine was sealed at both ends and a cannula exteriorized from its lumen to enable fermenting residues to escape. Pigs were housed in individual metabolism crates. Digesta by-passed the large intestine, were expelled via the anus and collected in trays. The spurious influence of bacteria in the large intestine, on digestibility measurement, was thus avoided.