Effect of Forage Types Differing in Undigested Neutral Detergent Fiber Concentration and Forage Inclusion Rate on Reticulo-Ruminal Motility and Fermentation, Total Tract Barrier Function, and Blood Metabolites of Finishing Beef Heifers.

This study evaluated the effects of the forages (barley silage [BarS] vs. straw [STR]) that differ in the undigested neutral detergent fiber (uNDF) concentration and forage inclusion (FI) rate on ruminal fermentation, total tract barrier function, reticulo-ruminal motility, and blood metabolites of beef heifers. Six ruminally cannulated Hereford × Simmental heifers (699 ± 69.1 kg BW) were used in a 6 × 6 Latin square (26 d periods) with a 2 × 3 factorial treatment arrangement. However, 1 heifer was removed from the study after period 2 due to health problems unrelated to treatment, resulting in an incomplete 6 6 Latin square design. Barley grain-based diets were formulated using barley silage or wheat straw to provide alter uNDF (7.1 vs. 8.5% dry matter [DM]) with FI rates of 5, 10, or 15% of DM. There were limited interactions between forage type and FI. Dry matter intake was not affected (P ≥ 0.10) by forage type or FI. Use of STR vs. BarS increased uNDF intake (P < 0.001). Increasing FI increased (P < 0.001) uNDF intake for those fed 15% forage. Ruminal pH was not affected (P ≥ 0.10) by forage type; however, cattle fed 5% FI had lesser (P = 0.017) mean ruminal pH and maximum pH (P = 0.018) than those fed 10 and 15% of forage. Total short-chain fatty acid concentration was not affected by forage type (P = 0.84) but cattle fed the 5% FI rate had lesser (P < 0.001) molar proportion of acetate when compared with cattle fed 10% and 15% forage. Increasing FI rate decreased molar proportion of propionate (P < 0.001). Feeding STR relative to BarS decreased (P = 0.041) the reticulo-ruminal contraction duration. In contrast, cattle fed the 10 and 15% FI rates had greater (P = 0.028) contraction frequency with lower (P = 0.048) contraction area than those fed 5% forage. Plasma glucose, serum insulin, and serum amyloid A were not affected by forage type or FI rate (P ≥ 0.10). Cattle fed 15% forage had lesser (P = 0.040) concentration of serum haptoglobin when compared with cattle fed 5 or 10% forage. In conclusion, forage type, used to affect the dietary uNDF concentration, and FI rate act independently suggesting that provision of STR to increase uNDF reduces reticulo-ruminal contraction duration and total tract permeability but may not affect ruminal pH. Increasing the FI increased dietary uNDF, stabilized ruminal pH, stimulated more frequent reticulo-ruminal contractions, and may decrease permeability of the gastrointestinal tract and systemic inflammation.