The effects of treated straw meal on ileal and faecal digestibility of nutrients in pigs.

Four 40 kg castrated male pigs fitted with simple 'T' cannulas in the terminal ileum were given diets of varying crude fibre content in a change-over experiment with two periods. The basal diet was composed of wheat and fishmeal supplemented with minerals and vitamins. To this was added varying levels of partially hydrolysed straw meal to give crude fibre contents ranging from 40 to 132 g/kg. After adaptation to the particular levels of straw meal, faeces and ileal digesta were collected during successive 24 h periods. Nutrient digestibility values were determined by the chromic oxide ratio method. The addition of treated straw meal to the diet had little or no influence on the DM content of digesta or faeces. The excretion of N in faeces increased with increasing fibre intake but there was no effect on urine N excretion. The overall apparent digestibility of N was reduced from 89 to 79% as crude fibre intake increased from 40 to 132 g/kg but ileal apparent digestibility of N remained constant at about 68%, suggesting that the effect was mediated through hindgut bacteria. Increased fibre intake caused increased net secretion of Na in the small intestine and reduced the apparent absorption of P in the large intestine.