Influence of dietary forage level and forage coarseness of grind on growth performance and digestive function in feedlot steers.

We conducted two trials to examine the influence of dietary forage level (FL; 16 and 8% sudangrass hay) and forage coarseness of grind (COG; ground to pass through a 2.5- vs 7.6-cm diameter screen) on growth performance and digestive function in feedlot steers fed a steam-flaked corn-based finishing diet. Thirty-two Mexican crossbred steers (297 kg) were used to determine treatment effects on growth performance during an 80-d finishing period. There were no treatment interactions (P > .10). Reducing FL increased (17%, P < .05) ADG. decreased (23%, P < .01) feed/gain, and increased (17% and 22%, P < .01) dietary NEm and NEg. Coarseness of grind did not affect (P > .10) steer performance. Treatment effects on digestive function were evaluated using four Holstein steers with cannulas in the rumen and proximal duodenum. There were no treatment interactions (P > .10) on nutrient digestibility. Forage level did not affect (P > .10) ruminal digestion of OM, N, or microbial efficiency. However, decreasing FL increased (P < .05) total tract digestion of OM (5.0%), N (5.7%), and ME (8.7%). Increasing COG increased total tract digestibility of OM (2.3%, P < .01), ADF (24.4%, P < .01); N (3.8%, P < .01), and ME (3.7%, P < .05). Increasing FL increased (P < .10) ruminal pH and decreased (P < .10) ruminal molar proportions of butyrate. Increasing COG did not influence (P > .10) ruminal pH or ruminal VFA molar proportions. We conclude that increasing coarseness of ground sudangrass may not improve the performance of feedlot steers when the forage is fed at either 8 or 16% of diet DM, although measures of ruminal and total tract nutrient digestibility may be slightly increased.