PSX-25 In situ ruminal degradation of feedstuffs in beef cattle fed finishing diets with varying starch levels.

Abstract Two in situ trials were conducted to investigate the ruminal degradability of sugarcane bagasse, corn, and sorghum in beef cattle fed finishing diets with varying starch levels. Four ruminally cannulated Nellore steers (494.8±55.9 kg) were housed in individual pens (21 m²). In Trial 1, steers were assigned to a replicated 2×2 Latin square design, following a 2×2 factorial arrangement of treatments. Steers were fed two starch levels [22.5% vs. 45.0% of diet dry matter (DM)] and two sugarcane bagasse sources [fresh vs. aged (1 year old)], which were incubated in the rumen for 48, 72, and 120-h. Sugarcane bagasse was incubated from days 9 to 14 of each experimental period, to evaluate DM and neutral detergent fiber (NDF) degradation. In trial 2, steers were assigned to a replicated 2×2 Latin square design, following a 2×2×2 factorial arrangement of treatments, including two starch levels (22.5% vs. 45.0% of the diet DM), two-grain types (corn vs. sorghum), and two-grain processing methods (ensiled reconstituted high-moisture vs. dry-rolled), which were incubated in the rumen for 7 hours. Corn and sorghum were incubated on day 14 of each experimental period to evaluate DM and starch degradation. Each period lasted 21 days. All dried samples were ground to pass a 2-mm screen, and 1.5 grams were weighed in triplicate into nylon bags (50-μm) and inserted into the ventral rumen in a mesh laundry bag in reverse order. In trial 1, aged sugarcane bagasse had greater DM (P=0.03) and NDF (P=0.05) degradability than fresh bagasse. Bagasse incubated for 120-h had greater DM (P < 0.01) and NDF (P < 0.01) degradability, 72-h was intermediate, and 48-h had lower ruminal degradability. In trial 2, corn had greater (P < 0.01) ruminal degradation of DM and starch than sorghum. High-moisture grain had greater (P≤0.04) ruminal degradation of DM and starch than dry-rolled. At low starch levels, corn had greater (interaction, P=0.05) ruminal starch degradation than sorghum, while corn and sorghum at high starch levels were intermediate but not different. High-moisture had greater (interaction, P≤0.05) ruminal degradation of starch at both high and low starch levels compared to dry-rolled. High-moisture corn and sorghum had greater (interaction, P < 0.05) ruminal DM and starch degradation than their dry processing. In conclusion, diet starch levels did not affect DM, NDF, or starch in situ ruminal degradability of sugarcane bagasse, corn and sorghum. Aged sugarcane bagasse had greater ruminal degradability than fresh bagasse. Corn demonstrated greater ruminal degradability of DM and starch than sorghum when steers where fed diets low in starch. High-moisture improved in situ DM and starch degradation of both grain types when compared to dry processing. These findings highlight the influence of ingredient type, and processing method on ruminal degradability.