Comparative effects of processing methods on the feeding value of maize in feedlot cattle.

The primary reason for processing maize is to enhance feeding value. Total tract starch digestion is similar for coarsely processed (dry rolled, cracked) dry maize. Enhancements in starch digestion due to dry rolling maize v. feeding maize whole may be greater in light-weight calves than in yearlings, and when DM intake is restricted ( < 1·5 % of body weight). The net energy (NE) maintain (NEm) and NE gain (NEg) values for whole maize are 8·83 and 6·02 MJ (2·11 and 1·44 Mcal)/kg, respectively. Compared with conventional dry processing (i.e. coarse rolled, cracked), finely processing maize may increase the initial rate of digestion, but does not improve total tract starch digestion. Tempering before rolling (without the addition of steam) may enhance the growth performance response and the NE value of maize. Average total tract starch digestion is similar for high-moisture and steam-flaked maize. However, the proportion of starch digested ruminally is greater (about 8 %) for high-moisture maize. The growth performance response of feedlot cattle to the feeding of high-moisture maize is highly variable. Although the NEm and NEg value of whole high-moisture maize was slightly less than that of dry processed maize (averaging 9·04 and 6·44 MJ (2·16 and 1·54 Mcal)/kg, respectively), grinding or rolling high-moisture maize before ensiling increased (6 %) its NE value. Substituting steam-flaked maize for dry processed maize increases average daily gain (6·3 %) and decreases DM intake (5 %). The comparative NEm and NEg values for steam-flaked maize at optimal processing (density = 0·34 kg/l) are 10·04 and 7·07 MJ (2·40 and 1·69 Mcal)/kg, respectively. These NE values are greater (3 %) than current tabular values (National Research Council, 2000), being more consistent with earlier standards (National Research Council, 1984). When maize is the primary or sole source of starch in the diet, concentration of starch in faeces (faecal starch, % of DM) of feedlot steers can serve as an indicator of total tract starch digestion, and, hence, the feeding value of maize.