Effects of Miscanthus grass as a fiber source in pet diets on extrusion processing and diet utilization by dogs and cats



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Gastrointestinal health, digesta passage, regularity and consistency of elimination, and energy dilution of the diet can be affected by dietary fiber. Cellulose and beet pulp have been common fibers used in pet foods. Pet owners and pet food companies are in search of alternatives. Miscanthus grass is an ingredient produced from the dried canes of Miscanthus giganteus, a C4 grass grown for its high fiber content; however, it has not previously been evaluated in pet foods. Thus, the objectives were to determine the effect of Miscanthus grass on processing, nutrient utilization, hairball management, and fermentation end products. Pet foods were produced in a pilot scale extruder (E525, Extru-Tech, Sabetha, KS), dried to less than 10% moisture, then coated with chicken fat and flavor enhancer. Extrusion parameters (preconditioner and barrel water and steam addition, preconditioner discharge temperature, screw speed, die pressure, diet temperature, knife speed, specific mechanical energy, total mass flow, and wet bulk density) and kibble characteristics (kibble length, diameter, volume, density, sectional expansion ratio index, hardness, and compression energy) were evaluated for dog and cat foods produced with 10% Miscanthus grass, cellulose, or beet pulp. Miscanthus grass and cellulose dog diets required less specific mechanical energy. Additionally, these two canine diets were less dense than the beet pulp containing diet. Pet foods were fed to dogs and cats to evaluate nutrient digestibility and stool quality. Generally, dry matter, organic matter, and gross energy digestibility were lower for animals fed Miscanthus grass and cellulose diets than beet pulp diet. However, crude protein digestibility was higher for animals fed Miscanthus grass and cellulose diets compared to beet pulp diet. In both dog and cat studies, feces were softer when animals were fed the beet pulp diet. For cats, hairball management was evaluated by feeding a diet with 10% Miscanthus grass versus a non-fiber containing control diet. Most parameters evaluated (fecal hairball count, hair masses per day, average hairball size, total hair weight) were not affected by inclusion of Miscanthus grass, but there was a trend for more hair collected on the strainer (P = 0.0884), less total hair per gram of dry feces, and less hair masses per gram of dry feces (P < 0.05). Finally, to evaluate the effects of colonic fermentation an in vitro model used canine feces as the inoculum. Five fiber sources (Miscanthus grass, cellulose, beet pulp, pea fiber, and sorghum bran) were incubated (0, 4, 8, 12h) to determine organic matter disappearance and short chain fatty acid production. Beet pulp had a higher concentration of acetate, propionate, butyrate, and total volatile fatty acids compared to all other fiber sources. Sorghum bran produced the highest amount of isobutyrate and isovalerate compared to other test fibers. Miscanthus and cellulose were very poorly fermented and generally did not differ from each other. Therefore, Miscanthus grass is an alternative fiber source that compares favorably to cellulose in dogs and cat foods without affecting processing parameters, nutrient utilization, and fermentation end products.



Miscanthus grass, Dietary fiber, Extrusion, Nutrient utilization, Hairball, In vitro fermentation

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Doctor of Philosophy


Department of Grain Science and Industry

Major Professor

Greg Aldrich