Exogenous carbohydrases can be used in diets for pigs to increase digestibility of dietary fiber and energy in cereal grains and cereal co-products. The three main fibers in cereal grains and cereal co-products are arabinoxylans, cellulose, and mixed-linked beta glucans. The fermentability is different among these three types of fiber. Energy digestibility is often improved if xylanase is added to wheat-based diets, whereas positive responses to xylanase in corn-based diets have been difficult to demonstrate, indicating that fermentation of dietary fiber differs among ingredients. However, there is less information about effects of carbohydrases on digestibility of fiber and energy in sorghum-based diets. Therefore, an experiment was conducted to test the hypothesis that xylanase and cellulase improve the digestibility of energy and total dietary fiber in diets based on corn or sorghum with addition of high fiber co-products.

Animals, Housing, Experimental design, and diets

A total of 144 growing pigs with an average initial BW of 61.71 ± 5.39 kg were allotted to a randomized complete block design with 4 blocks of 36 pigs, 12 diets, and 3 pigs per diet in each block. Therefore, there were 12 replicate pigs per diet. A corn-soybean meal diet and a sorghum-soybean meal diet were formulated, and 2 diets based on corn, soybean meal, and 40% distillers dried grains with solubles (DDGS) or corn, soybean meal, and 40% wheat middlings were also formulated. Two additional diets based on sorghum, soybean meal, and 40% DDGS, or sorghum, soybean meal, and 40% wheat middlings were also be formulated. All diets were fed both without and with a xylanase-cellulase mixture that was sourced from Archer Daniels Midland Company, Decatur, IL. Vitamins and minerals were included in all diets to meet or exceed the estimated nutrient requirements for growing pigs.

Diets were fed to pigs for 24 days. During the initial 12 days, pigs were housed individually and diets were provided on an ad libitum basis during this period. On d 13, pigs were moved to individual metabolism crates and they were adopted to the crates for 4 days (d 13 to 16). Urine and feces were collected from the feed fed from d 17 to 22. In the metabolism crates, pigs were fed 3.2 times the maintenance energy requirement and water was available at all times.

Following chemical analysis, total tract digestibility (ATTD) of DM, energy and total dietary fiber was calculated for each diet and the DE and ME in all diets was calculated. Data were analyzed following a 2 × 2 × 3 design with two types of diets (corn based or sorghum based), two microbial enzymes treatments (none or enzyme), and three co-product inclusion to the diets (none, DDGS, or wheat middlings) using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) with pig as the experimental unit.

Results

The ATTD of DM was lower (P < 0.01) in diets with inclusion of wheat middlings than in diets with no inclusion of co-products or diets with inclusion of DDGS (Table 1) and the ATTD of total dietary fiber was lower (P < 0.01) if a co-product was included in the diet than if no co-product was used. However, the reduction was greater (P < 0.05) if the co-product was added to the sorghum based diets than if added to the corn-based diets (grain source × by-product interaction, P < 0.05). The ATTD of GE also decreased (P < 0.01) with co-products in the diets. However, this reduction was greater if co-product was added to the corn-based diets than if added to the sorghum based diets (grain source × by-product interaction, P < 0.01). Regardless of grain source, the ATTD of GE improved (P < 0.01) if the enzyme mix was added to the diets. The concentration of DE and ME was greater (P < 0.01) in sorghum-based diets than in corn-based diets, but DE and ME decreased (P < 0.01) if a co-product was added to the diet. Addition of enzymes improved (P < 0.01) the concentration of DE and ME in all diets regardless of grain sources or co-product inclusion.

Key points

• Total tract digestibility of energy and DE and ME in corn based as well as sorghum-based diets increased if diets were supplemented with a xylanase-cellulase enzyme mix regardless of grain source and fiber concentration.

• The improved DE and ME that was caused by the enzyme mix was not a result of increased digestibility of total dietary fiber.

Table 1. Apparent total tract digestibility (ATTD) of energy and nutrients, and concentrations of digestible and metabolizable energy of experimental diets fed to pigs¹

¹Data are least squares means of 12 observations per treatment.

²GE = gross energy; DM = dry matter.

³TDF = total dietary fiber.

⁴DE = digestible energy; ME = metabolizable energy.

⁵SBM = soybean meal; DDGS = distillers dried grains with solubles.

⁶Enz = enzyme premix supplied by ADM Animal Nutrition, Quincy, IL, USA.