Ileal amino acid digestibility assay for the growing meat chicken--effect of the imposition of a fasting period and the nature of the test diet.

1. The objective of this study was to investigate the effects of cold-pelleting, the length of the fasting period before feeding of the test diet and the nature of the test diet on apparent ileal nitrogen (N) digestibility in the broiler chicken. 2. Four-week-old broiler chickens were given a pelleted or non-pelleted maize/soyabean meal (basal) diet. The birds were starved for 24 h, given a single test meal (25 g) by intubation and killed 4 h after the start of feeding by administration of a barbiturate, to allow sampling of ileal digesta (terminal 15 cm). Cold-pelleting did not affect apparent ileal N digestibility. 3. Four-week-old broiler chickens were fasted for 12 or 24 h and then received a test meal (1 h free access) of either a pelleted soyabean meal or a pelleted meat-and-bone meal diet or were continuously fed on one of the two diets. The imposition of a fast did not affect apparent ileal N digestibility. However, a 24 h fasting procedure was preferred, as the between animal variation for apparent ileal N digestibility was lower than for the 12 h fast or for continuous feeding. 4. Four-week-old broiler chickens were given either semi-synthetic starch-based diets containing maize, wheat bran, meat-and-bone meal or fish meal as the sole sources of protein or each of these diets in combination with the basal diet (50:50 on a dry matter basis). With the exception of the maize diet, the apparent ileal N digestibility values calculated by correcting for the digestibility of the basal dietary component were significantly lower than when digestibility was determined directly using a diet in which the respective proteins were the sole protein source. This implies that interactions between the dietary ingredients influence estimates of apparent ileal N digestibility.