Fiber in Animal Nutrition

63 Fecal volume In-vitro fermentation of cellulose was equally low for feces derived from dogs fed a dry diet containing 8% cellulose or 14.5% beet pulp for 26 days (Sunvold et al., 1995b). The data indicate that cellulose is hardly fermented in the colon of dogs and cats and that a high- cellulose diet does not stimulate bacterial fermentation. 5.2.3 Cellulose and energy digestibility In addition to its impact as caloric diluter, cellulose inclusion lowers the energy value of petfood by interference with the digestion of carbohydrates (nitrogen-free extract) and proteins, which are calorie-yielding nutrients. Therefore, an accurate estimate of the meta- bolizable energy content of fiber-enhanced foods can only be determined by animal ex- periments rather than by predictive equations. Digestibility studies in dogs show that mixing a wet food with cellulose lowers the apparent digestibility of dietary carbohydrates and proteins (Dobenecker and Kienzle, 1998; Kienzle et al., 2001; Lewis et al., 1994). The lowering effect was found to be dose- dependent when a wet food was mixed with 3, 6 or 9% cellulose (Burrows et al., 1982). For commercial dry dog foods, an increase in 1.5% units of crude fiber in the dietary dry matter is associatedwith a 1%unit decrease in the apparent digestibility of energy (Kienzle et al., 1998; 2006). When cellulose was mixed with a moist complete food or a mixture of beef shoulder muscles and a vitamin-mineral mix, to a level of 17 or 24% in the dietary dry matter, apparent protein and carbohydrate digestion was reduced in cats (Kienzle et al., 1991; Prola et al., 2010). Such effect was also seen by Fekete et al. (2004) who added cellulose-rich peanut hulls to a wet food. For commercial dry cat foods, a negative, linear relationship has been reported for the amount of total dietary fiber and apparent energy digestibility (Kienzle et al., 2006). 5.3 Fecal volume Dogs excrete with their feces more bulk, water and dry matter when substantial amounts of cellulose are added to their wet food containing about 1% crude fiber in the dry matter (Burrows et al., 1982; Kienzle et al., 2001; Lewis et al., 1994). The increase in fecal volume is explained by the facts that the added cellulose is indigestible and depresses the apparent digestibility of dietary dry matter. Cellulose feeding does not increase the percentage of water in feces (Burrows et al., 1982; Kienzle et al., 2001; Lewis et al., 1994). Because cellulose is poorly fermentable, the concentration of short-chain fatty acids in feces may remain unchanged. This will also hold for the colonic content so that osmotic pressure is not raised. Water is not pulled into the lumen and does not end up in the feces. This effect in combination with a higher digestibility of dietary dry matter explains that cellulose, when compared with certain other types of fibers, may diminish fecal bulk. To dog owners, feces consistency and vo- lume are indicators of intestinal health and food quality. Well formed stools that are not too moist and loose, and not too dry and hard, are gladly seen and so is low feces volume associated low defecation frequency. Adding cellulose has been shown to prevent diarrhea when dogs are fed a fiber-free diet, but it increases feces volume. As described below, it has been demonstrated that ligno- cellulose versus wheat bran or beet pulp, at a constant level of dietary crude fiber, © ERLING Verlag