The apparent and true ileal digestibility of nitrogen and amino acids in lactic casein for the growing pig

Abstract

The apparent and true ileal digestibility of nitrogen and amino acids in lactic casein were determined in the growing pig. A semi-synthetic diet containing lactic casein as the sole protein source was given to 12 pigs at three levels of feeding and following slaughter, samples of ileal digesta were collected from the terminal ileum. Estimates of endogenous ileal nitrogen and amino acid excretion, determined in a separate study by feeding pigs a protein-free diet, were used to calculate the true digestibility. The effect of sampling site within the ileum on the apparent digestibility of nitrogen was investigated at the highest feeding rate. Level of feeding of the casein diet did not influence the apparent digestibility of nitrogen or amino acids. Apparent estimates of digestibility ranged from 0.67 for glycine to 0.98 for lysine, methionine, tyrosine and phenylalanine, whilst the true values ranged from 0.92 for serine to 1.04 for proline, glycine, phenylalanine and tyrosine. Sampling site over the final 140 cm of ileum did not influence apparent digestibility of casein nitrogen. It was concluded that casein protein was virtually completely digested and absorbed anterior to the terminal ileum of the growing pig. On this basis, regression equations were derived showing the influence of dietary dry matter intake on ileal endogenous amino acid excretion.