SIGNIFICANCE OF ENDOGENOUS GUT NITROGEN LOSSES IN THE NUTRITION OF GROWING PIGS - A REVIEW

During the past two decades endogenous gut N losses (ENL) at the dista l ileum in the growing pig have received considerable attention in swi ne nutrition research. Estimates of ENL are important for determining true ileal N and amino acid digestibilities and for identifying means to improve the efficiency of N and energy utilization in growing pigs. Endogenous secretions originate from various sources including saliva , pancreatic secretions, bile, sloughed off epithelial cells, serum al bumin and mucin. It has been estimated that 70 to 80% of endogenous N secretions are digested and re-absorbed. Therefore, ENL represents onl y a fraction of total endogenous N secreted into the gut. Increased EN L are likely associated with elevated rates of gut protein synthesis. This is bound to increase maintenance energy and amino acid requiremen ts of pigs. Traditionally, ENL were determined by feeding protein-free diets or by the regression method. Various alternative techniques (N- 15-isotope dilution technique, homoarginine technique, enzymatically h ydrolysed casein method) are now available to estimate the ENL in pigs fed protein-containing diets. Each of these techniques has some limit ations and all require different assumptions. Results obtained with th ese alternative techniques indicate that the net ENL losses are much h igher and more variable than previously estimated, and that they are a ffected both by animal and dietary factors. Recent estimates of ENL lo sses vary between 1.8 and 8.3 g kg(-1) dry matter intake. The main fac tors (feed intake, body weight, content of anti-nutritional factors, f ibres and [digestible] protein) that affect ENL and approaches (plant breeding and selection, ingredient processing and use of exogenous enz ymes) to reduce ENL are discussed in this review. In addition, the met abolic costs associated with ENL are estimated.