Cereal coproducts used as energy source for feeding pigs has increased in the last decade in the United States. However, a major concern is batch-to-batch variation and limited information about the quality of coproducts available. Wheat middlings is the most common wheat coproduct used in animal feeding, and red dog is also produced in some wheat mills (mix of fiber and endosperm fractions from wheat grain). The present study was designed to determine the nutrient composition and apparent total tract digestibility (ATTD) of GE, DM, OM, and NDF and the concentration of DE and ME in 10 sources of wheat middlings and in 1 source of red dog from different flour mills in the United States. Twelve growing pigs (31.0 ± 1.0 kg of initial BW) were randomly allotted to a 12 × 8 Youden square design with 12 dietary treatments and eight 14-d periods. Pigs were individually housed in metabolism crates for total collection of feces and urine. A corn-soybean meal basal diet, and 11 diets containing corn, soybean meal, and 39.4% of one of the 10 sources of wheat middlings or red dog were formulated. In all diets, the ATTD of GE, DM, OM, and NDF was calculated using the direct procedure, and the ATTD of GE, DM, OM, and NDF in each source of wheat middlings or red dog was calculated by difference. Furthermore, the values for DE and ME were also calculated.
The average concentration of CP was 17.67% in wheat midlings and 17.0% in red dog, and the concentration of acid hydrolyzed ether extract (AEE) and total dietary fiber (TDF) were 2.44 and 13.90% in red dog, but 4.07 and 36.45% in wheat middlings. More starch (42.98%) was detected in red dog compared with wheat middlings (20.28%). Similarly, red dog had greater bulk density (498.5 g/L) and smaller particle size (146 µm) than wheat middlings (315.1 g/L and 783 µm). The average ATTD of GE, DM, OM, and NDF in wheat middlings (67.2%, 71.2%, 72.9%, and 53.0%, respectively) was less than in red dog (79.35%, 82.9%, 86.6%, and 58.7%, respectively). The DE and ME average concentrations in wheat middlings were 2,990 and 2,893 kcal/kg DM, and these values were lower than the DE and ME in red dog (3,408 and 3,292 kcal/kg DM).
In conclusion, the nutrient composition of the wheat middlings used in this experiment generally had limited variability, but the fractions that were most variable were the concentration of starch, NDF, and TDF. The concentration of starch in red dog was greater than in wheat middlings, but the concentration of NDF and TDF was lower. Variation in ATTD of GE and nutrients among the 10 sources of wheat middlings was low, but the ATTD of GE and nutrients in red dog was greater than in wheat middlings. Differences in physical characteristics and concentration of starch and fiber are likely the main reason for the greater nutritional value observed of red dog compared with wheat middlings.
Casas, G. A., Rodriguez, D. A., and Stein, H. H. (2018). Nutrient composition and digestibility of energy and nutrients in wheat middlings and red dog fed to growing pigs. Journal of Animal Science, 96(1), 215-224. https://doi.org/10.1093/jas/skx010