522 - Late-Breaking: Effects of Corn Processing and Age on Energy Balance, Nutrient Digestion and Rumination in Cattle

Current library values for energy content in whole or dry-rolled corn (DRC) are identical and do not differ for cattle of different age (NASEM, 2016). Calves (295 ± 29 kg) and yearlings (521 ± 29 kg) were fed whole, DRC or steam-flaked corn (SFC) to evaluate library values of energy content in different types of processed corn among cattle of different age. Cattle were fed diets comprised of 75% corn (DM-basis) to 2.5-times maintenance energy requirements using estimates of NE_m in corn and SFC (NASEM, 2016). Data were analyzed using the MIXED procedure of SAS. There was no observed interaction of corn processing and cattle age (P ≥ 0.40). Time spent ruminating (min/d) was not different between dietary treatment or age. Total tract starch digestibility was greatest (P = 0.01) for cattle fed SFC (97.5%), intermediate in cattle fed DRC (92.4%) and least in cattle fed whole corn (89.5%). Nitrogen balance was not affected (P ≥ 0.30) by corn processing or age. Digestible and metabolizable energy (Mcal/kg-DMI) were greater (P ≤ 0.05) for cattle fed SFC compared to DRC or whole. A greater proportion of DE was lost to heat production (P = 0.01) in cattle fed whole corn compared to DRC and tended to be greater (P = 0.08) in cattle fed SFC than DRC. Retained energy (Mcal/d) should have been similar if current library values correctly reflect energy content in each type of processed corn. However, retained energy was greater (P < 0.01) for cattle fed DRC compared to whole corn and tended to be greater (P = 0.06) compared to SFC indicating that library values for DRC underestimate energy available to growing cattle. Measures of retained energy for cattle fed DRC indicated that energy available for gain from DRC was 42% greater than library values (NASEM, 2016).