Effects of forage intake to minimize the risk of subacute ruminal acidosis on performance of feedlot finishing cattle

Abstract Text: Growing beef cattle in North America are typically fed high grain diets with a limited amount of forage to maximize productivity cost-effectively. Distillers grains (DG) are now commonly fed as part of the concentrate lowering the amount of fermentable starch in the diet and the potential risk of ruminal acidosis. The objectives of the study were to determine the effects of varying the concentration of forage in barley-based diets containing DG on feed intake, growth performance, and carcass traits of feedlot finishing cattle. A uniform group of 160 cross-bred beef steers was stratified according to initial BW (349.7 ± 22.3 kg) and randomly allocated to 20 pens (5 pens of 8 steers per treatment). The treatments were barley silage at 0, 4, 8, and 12% of diet DM. The remainder of the diet consisted of 80, 76, 72, and 68% barley grain for the 4 diets, respectively, 15% corn dried DG and solubles, and 5% supplement (with monensin at 28 mg/kg diet DM). The diets were fed as a total mixed ration for ad libitum intake (minimum of 5% orts) once per day. Cattle were weighed on 2 consecutive d at the start and end of the experiment and on 1 d every 3 wk throughout the experiment (124 d). The DMI of each pen was determined from feed offered daily and orts at the end of each 3-wk period. The ADG was determined from linear regression of BW over time. Data for DMI for each pen, and BW, ADG, G:F, and carcass traits for each animal were analyzed as a completely randomized design using a mixed linear model with diet as a fixed effect, pen replicate and diet × pen replicate as random effects (except for the model for DMI), and pen as the experimental unit. There was a trend (P = 0.10) towards a linear increase in DMI by steers with increasing percentage of barley silage. However, there was no effect (P > 0.05) of the barley silage treatments on final shrunk BW (612.7 ± 4.25 kg), ADG (1.86 ± 0.03 kg/d), and carcass traits. Feed efficiency linearly decreased (P < 0.05) with increasing percentage of barley silage. Increasing the proportion of barley silage in a barley grain-based diet with DG may reduce the incidence of subacute ruminal acidosis but feed conversion efficiency is reduced.

Keywords: finishing cattle, forage, growth performance