Predicting Net Energy Value of Corn Silage Varying in Grain Content

Abstract

A 2-yr study was conducted to determine the relationships between acid detergent fiber (ADF), diet grain content, net energy (NE) value and performance of feedlot cattle. Regression equations were developed from pooled data involving 128 Charolais crossbred and Hereford steers fed diets that ranged in diet grain content from 30 to 96%. Acid detergent fiber was an adequate predictor of feedlot performance; it accounted for 78, 89 and 91% of the variation in gain, dry matter intake and feed efficiency, respectively. Diet grain content accounted for 87, 89 and 93% of the variation in gain, dry matter intake and feed efficiency, respectively. Diet grain content influenced ME (P = .02), NEm (P<.0005) and NEg (P<.0005). Corn silage containing 50% corn averaged 1.58 Mcal NEm/kg and 1.11 Mcal NEg/kg when fed alone, with a decrease of .06 Mcal NEm/kg and .05 Mcal NEg/kg for each 10 percentage unit decrease in corn grain content. Corn grain averaged 2.04 Mcal NEm/kg and 1.63 Meal NEg/kg when fed in an all concentrate diet. When energy values were determined by analysis of silage and silage plus grain diets (30 to 70%) vs high concentrate diets (70 to 96%) ME, NEm and NEg were 2.9, 4.3 and 8.9% lower than predicted for 30 to 70% grain diets, and ADF and diet grain content accounted for only 33 and 23% of the variation in NEg, respectively. In comparison, ADF and grain content accounted for 62 and 63% of the variation in NEg when diet grain increased from 70 to 96%. These data suggest that discounting whole plant corn silage and corn grain NEm values by 4.3% and NEg values by 8.9% when total diet corn grain content is between 50 and 80% will adjust for associative effects.