Page 85 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 85

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Figure 5-15. Protein structure (A) and formation of peptide bonds (B). The dotted lines show how the peptide bonds are formed, with the
production of water. R = the remainder of amino acids. For example, in glycine, R = (CH ) –COOH.
2 2
port of a well balanced mixture of amino acids from the intes- Apparent vs.True Digestibility
tinal lumen to the portal vein. Estimations of crude protein and amino acid availabilities of
Amino acids and proteins not absorbed in the small intestine most feed ingredients can be provided by determining appar-
can be fermented in the hindgut and produce fecal odor com- ent ileal protein and amino acid digestibilites. Apparent
pounds. These compounds are produced by bacterial enzymes digestibilities are determined by comparing the amounts of
during the degradation of endogenous and undigested food amino acids present in the feed and digesta without determin-
proteins.The fecal odor compounds include ammonia, aliphat- ing endogenous nitrogen losses. For determining true ileal
ic amines, indoles, phenols and volatile sulfur-containing com- amino acid digestibilities, undigested dietary amino acids pres-
pounds. These compounds not only affect fecal odors but can ent in the ileal digesta should be differentiated from endoge-
also seriously affect the GI health of animals (Hussein and nous amino acids. Recent studies suggest that endogenous
Sunvold, 2000). The amount of dietary amino acids that reach nitrogen losses are higher than previously estimated and that
the large intestine can alter fecal compounds. The amount of differences in apparent digestibilities between feedstuffs are
amino acids reaching the large intestine can be affected by high attributed to differences in endogenous gut nitrogen losses
food DM intake, high protein foods and foods that contain low rather than differences in true digestibilities (Nyachoti et al,
quality proteins. An increase in protein and amino acid flow to 1997). Factors such as body weight, dietary fiber content, DM
the large intestine can result in more substrate for the resident intake and the presence of anti-nutritive factors in the diet
bacteria and an increase in fecal odor components (Yamka et al, influence secretions and/or reabsorption of endogenous gut
2006; Hussein and Sunvold, 2000). protein (Nyachoti et al, 1997).
Many studies investigating altering fecal odor compounds Several methods exist for estimating the contribution of
have focused on the use of prebiotics. Researchers found that endogenous protein and amino acids at the distal ileum; three
feeding adult dogs FOS (0.5% of the DM) decreased are used most commonly. The first method is a direct method
putrescine, cadaverine, tyramine and total amines (Hussein for measuring endogenous protein. This method requires that
and Sunvold, 2000). This study demonstrated that fecal odor animals be fed a protein-free diet. It is assumed that the recov-
could be manipulated by prebiotics; however, few studies have ery of endogenous protein and amino acids at the distal ileum
focused on fecal components related to protein source. is the same for animals fed protein-free and protein-containing
Another study found that dogs consuming poultry by-prod- diets (Nissen, 1992; Burns et al, 1982; Kendall et al, 1982).The
uct meal produced more fecal odor compounds than dogs fed second method is the regression method. The regression
soy-based foods (Yamka et al, 2006). The reduction of fecal method determines endogenous protein and amino acid recov-
odor compounds in soy-fed dogs was likely the result of eries in digesta with the aid of regression to zero protein intake
hindgut fermentation of soluble fiber and oligosaccharides using a series of test source protein levels. However, with the
present in soy. regression method, no relationship is assumed between protein