Effects of Dietary Acetate and Propionate on Nutrient Digestibility, Ruminal Characteristics, and Performance by Steers Fed Diets Containing All-Concentrate or 20% Roughage1

Four experiments were conducted to evaluate the effects of dietary volatile fatty acids (VFA) on nutrient digestibility, ruminal characteristics, and growth performance by finishing steers. Diets were based on sorghum grain in Exp. 1 and 2, and corn in Exp. 3 and 4. Experiment 1 was a digestibility study with eight steers used in two 4 x 4 latin square arrangements of steers and diets. Diets in the first square were all-concentrate (C) with 1 or 2% acetate (A) or 2% propionate (P), and diets in the second square were 20% rice straw (RS) with 1 or 2% A or 2% P. In Exp. 2, steers (four per treatment) were individually fed C or RS basal diets with 1.72% A or 5.00% P added to the C diet, and 1.14% A or 3.33% P added to the RS diet based on expected intake. In Exp. 3 and 4, C diets were diluted with 1.65 or 0.55% A, respectively. These diets were further diluted with 20% rice hulls (RH) in Exp. 3, and 20% RH and 20% RS in Exp. 4. The C diet was also diluted with 20% RS in Exp. 3 and considered a positive control. Adding A, P, or RS to C diet based on sorghum grain had no effect (P>0.10) on energy digestibility or N retention. In Exp. 2, P reduced (P<0.05) DMI and ADG, compared with A. Acetate improved (P<0.05) DMI of C and RH diet in Exp. 3, but only the RH diet in Exp. 4. Likewise ADG and, in most cases, carcass weights were improved (P<0.05) by A in C and RH diets, but not in RS diets. Dietary P reduced (P<0.05) ruminal acetate levels and increased (P<0.05) ruminal propionate in Exp. 2. Acetate may have potential to improve DMI and ADG of steers consuming diets containing all-concentrate or poorly digestible roughage.