THE EFFECT OF BODY WEIGHT OF PIGS ON TRUE AND APPARENT ILEAL AMINO ACIDS DIGESTIBILITY OF RYE

It is generally accepted that the ability of pigs to digest protein increases with age. However, it has been shown that small pigs excreted more endogenous nitrogen (N) than large pigs. Consequently, the apparent amino acids (AA) digestibility may be lower in young pigs while true digestibility, which is corrected for endogenous losses, may be comparable with that found in older pigs. To test this hypothesis, six cannulated piglets (mean body weight 20.6 kg) fitted with a simple T-cannula at terminal ileum were used to estimate apparent and true digestibilities of AA and of total N in a rye-based diet (96 % rye). The digestibility study was repeated on the same pigs fed the same diet when they reached mean body weight 61.7 kg. The apparent ileal digestibilities of total AA and total N were significantly higher in heavier pigs than in piglets. Except for methionine and phenylalanine, the apparent digestibilities of individual AA showed a similar pattern. In contrast, there was no significant difference between piglets and heavier pigs for the true ileal digestibility of total N. True digestibility of most AA was lower in heavier pigs than in piglets, the differences for total and some individual AA being significant. The present results suggest that the higher apparent digestibility values found in heavier pigs as compared to piglets are due to the confounding effect of endogenous N losses rather than the better ability of older pigs to digest protein.