Effects of intake of linseed oil or tallow on nutrient digestion and nitrogen balance of beef steers consuming diets based on dry-rolled corn

Lipids can have detrimental effects on the ruminal microbiota and, subsequently, diet digestibility. We evaluated effects of amount and source of dietary lipid on nutrient digestibility, ruminal fermentation, and N balance in cattle consuming diets based on dry-rolled corn. Five steers (BW = 392 ± 15 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a 5 × 5 Latin square with 12-d periods. Diets contained no added lipid or 4 or 8% added lipid from either a tallow or linseed oil. Linseed oil tended (P = 0.08) to decrease DMI compared with tallow. Greater amounts of lipid tended to decrease ruminal digestion of DM (P = 0.07), OM (P = 0.14), and NDF (P = 0.05). Microbial efficiency (g of microbial N/kg of OM fermented) tended to increase (P = 0.10) with added lipid, but microbial N flow to the duodenum was not affected (P ≥ 0.19) by amount or source of lipid. Ruminal pH (P ≥ 0.83), ammonia (P ≥ 0.33), and total organic acid content (P ≥ 0.54) were not affected by diet lipid. Added dietary lipid tended (P = 0.10) to decrease ruminal acetate concentrations. Addition of a more unsaturated lipid (linseed oil) decreased (P = 0.05) total-tract NDF digestibility compared with a more saturated lipid (tallow), and addition of lipid tended to decrease digestion of DM (P = 0.13) and NDF (P = 0.08) compared with control. Linseed oil decreased (P < 0.01) fecal N and tended to reduce (P = 0.08) urinary N.