THE MEASUREMENT OF DIETARY AMINO-ACID DIGESTIBILITY IN PIGS, RATS ANDCHICKENS - A COMPARISON OF METHODOLOGIES

In a collaborative study between three centres several methods of esti mating ileal digestibility of protein and amino acids were compared. T here were five trials with pigs, each with three to four animals: one with T-cannulas (TC), one with postvalve ileocolic re-entrant cannulas (IPVC) and three using end-to-end ileorectal anastomosis (IRA). There was one trial with 18 rats with end-to-end ileorectal anastomosis and two trials with 12 intact and 12 caecectomised cockerels. Three isoni trogenous diets were used: one based on barley (B), one based on dried milk (M) and one which was a mixture of the other two (BM). Diet B wa s reground for pigs with IPVC to avoid cannula blockage and also for r ats because of feed refusals. The reground diet was also tested with I RA pigs. True digestibility was calculated by correction for endogenou s losses using values obtained with protein-free diets. Overall mean d igestibility of nitrogen and amino acids, both for apparent and true d igestibility, was higher for IPVC (apparent 0.83; true 0.92) than for the other pig trials, which gave similar mean values (apparent 0.71-0. 74; true 0.83-0.85). Mean values with rats were similar to these (0.75 and 0.83 respectively). Mean apparent digestibility was lowest with c ockerels (0.66), but true digestibility values (0.86) were similar to those of the pigs (except IPVC) and rats. However, trials giving the s ame or similar mean values ranked individual diets differently. Analys is of the correlations between trials showed that the pattern of varia tion between trials was similar for most amino acids. In this respect, the trials with cockerels were distinctly different from those with p igs and rats, giving lower digestibility of theronine, serine and cyst ine. In all trials, the digestibility, both apparent and true, of Diet BM was essentially equal to that expected from the estimates with Die ts B and M.