Evaluation of a Forage-Fat Blend as an Isocaloric Substitute for Steam-Flaked Wheat in Finishing Diets for Feedlot Cattle: Growth Performance and Digestive Function

Abstract

Two trials were conducted to evaluate the addition of a forage-fat blend (FFB) as a substitute for grain in finishing diets for feedlot cattle. Treatments consisted of a steam-flaked wheat-based finishing diet containing 15, 29, or 45% FFB. The FFB contained 80% chopped alfalfa hay and 20% yellow grease and was formulated to have NEm and NEg values similar to that of wheat. In Trial 1, 126 crossbred steers (225 ± 5.4 kg) were used to evaluate treatment effects on growth performance and dietary NE. In Trial 2, three Holstein steers (448 ± 21 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on characteristics of digestion. Increasing the FFB did not affect (P>0.10) ADG, but decreased gain efficiency (linear effect, P<0.05) and dietary NE concentration (linear effect, P<0.01). Increasing the FFB did not affect (P>0.10) ruminal digestion of starch, N, or microbial N (MN) efficiency, but decreased (linear effect, P<0.10) ruminal digestion of OM and increased (linear effect, P<0.10) ruminal digestion of ADF. Increasing the FFB did not affect (P>0.10) postruminal digestion of OM, starch, and N, but decreased postruminal digestion of fatty acids (linear effect, P<0.05). Increasing the FFB did not affect (P>0.10) percentage of total tract starch, N, and ADF digestion, but decreased the percentage of total tract digestion of OM (linear effect, P<0.01) and DE (linear effect, P<0.05). We conclude that an isocaloric FFB can replace grain at levels of up to 45% of dietary DM without affecting ADG in feedlot cattle. However, when dietary inclusion rates are > 15%, dietary NE and, hence, BW gain efficiency may decrease. The magnitude of the effect of FFB inclusion rate on energy recovery is a predictable function of the relationship between fatty acid intake and intestinal fatty acid digestion.