Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/13/2013
Publication Date: 1/20/2014
Publication URL: http://handle.nal.usda.gov/10113/58318
Citation: Hales, K.E., Brown-Brandl, T.M., Freetly, H.C. 2014. Effects of decreased dietary roughage concentration on energy metabolism and nutrient balance in finishing beef cattle. Journal of Animal Science. 92(1):264-271. Interpretive Summary: The optimal roughage concentration in feedlot diets changes continuously for many reasons such as source, availability, price, and interaction with other ingredients in the diet. We hypothesized that roughage concentration in feedlot diets containing a moderate level of wet distillers grains with solubles could be reduced because of the high amount of fiber contained in the distillers grains. The effects of roughage concentration in dry-rolled corn diets containing wet distillers grains with solubles on energy metabolism and nutrient balance were evaluated in beef steers. Our results demonstrate that nutrient retention in feedlot cattle can be improved by reducing the amount of alfalfa hay used in finishing diets containing at least 25% wet distillers grains with solubles.
Technical Abstract: The optimal roughage concentration required in feedlot diets changes continuously for many reasons such as source, availability, price, and interaction with other ingredients in the diet. Wet distillers grains and solubles (WDGS) are common in finishing diets and they contain relatively high amounts of fiber compared with other grains they replace (Klopfenstein et al., 2008). Therefore, concentration of roughage could be altered when WDGS are included in feedlot diets. There has been very little data published regarding the effects of roughage concentration on energy metabolism and nutrient balance in beef steers. Therefore, the effects of roughage concentration in dry-rolled corn (DRC)-based diets containing 25% WDGS were evaluated in 8 steers (BW = 362 kg) using a replicated Latin square. Data were analyzed with the fixed effects of dietary treatment and period and random effects of square and steer within square were included in the model. Diets consisted of 25% WDGS and the balance being DRC and coarsely ground alfalfa hay (AH) replacing corn at 2% (AH-2), 6% (AH-6), 10% (AH-10), and 14% (AH-14) of dietary dry matter. As a proportion of GE intake, fecal energy loss increased linearly (P = 0.02), and DE decreased linearly (P = 0.02) as dietary level of AH increased. Methane energy loss, as a proportion of GE intake, increased linearly (P < 0.01) and ME decreased linearly (P < 0.01) as dietary concentration of AH increased. Heat production tended (P = 0.10) to decrease reaching a minimum of 10% AH, and increasing from 10% to 14% AH inclusion. Moreover, as a proportion of GE intake, retained energy (RE) decreased (P < 0.01) as AH level increased in the diet. Reasons for the decrease in RE are: 1) the increase in fecal energy loss that is associated with decreased ruminal digestibility of NDF when AH replaced DRC and the shift in ruminal VFA produced, 2) the decreased energy available for animal retention when NDF increased linearly as AH increased in the diet, and 3) the methane and heat energy associated with digestion of the fibrous portion of the AH. Neutral detergent fiber and OM excretion also increased linearly (P < 0.01) with increasing AH in the diet. The increased NDF and OM excretion were likely caused by the difference in digestibility of AH and DRC.