Effects of Urea and Distillers Inclusion in Finishing Diets on Steer Performance and Carcass Characteristics

Crossbred steers (n = 432; initial BW = 285 ± 24 kg) were utilized to study the effects of wet distillers grains and urea inclusion in finishing diets on performance and carcass characteristics. Distillers grains (DGS) have 63% RUP as a % of CP; suggesting RDP in finishing diets with distillers grains may be deficient without recycling of excess metabolizable protein. A randomized block design study with a 3×3 factorial arrangement of treatments was performed with six replications per treatment. One block was removed prior to analysis of carcass data due to missing data points leaving four replications per treatment for carcass characteristics. Factors included three inclusions of DGS (10%, 15%, or 20% of diet DM) and three inclusions of urea (0%, 0.5%, or 1% of diet DM). Blood samples were collected after cattle were fully adapted to finishing diets on d 30 of the trial and 80 days later on d 110 of the trial for analysis of plasma urea nitrogen (PUN) levels. A quadratic interaction (P < 0.05) between urea inclusion and DGS inclusion was observed for G:F. Diets containing 20% DGS had the greatest G:F when 0% urea was included. In diets containing 0.5% urea G:F was lowest for the 10% DGS diet and highest for the 15% DGS diet with 20% DGS diet being intermediate. For diets with 1% urea the 10% DGS diet had the lowest G:F, 15% DGS was intermediate and the 20% DGS diet was greatest. There were no other interactions observed (P > 0.11). There was a tendency (P < 0.08) for a linear increase in ADG with increasing inclusion of DGS. A linear decrease (P <0.01) in DMI was observed for increasing DGS levels. A linear increase in 12^th rib fat and PUN was also observed for increasing levels of DGS. There was a tendency (P = 0.08) for a quadratic effect of urea inclusion on live ADG with cattle being fed 0% urea having the lowest ADG and cattle fed 0.5% urea having the greatest ADG with cattle fed 1.0% being intermediate. A linear increase (P < 0.01) in PUN level was observed as levels of urea increased. Increasing inclusion of DGS from 10 to 20% of diet DM increased ADG, G:F, and HCW. Additionally, as urea and DGS were increased together G:F was improved suggesting insufficient recycling when less than 20% distillers grains are fed.