Ruminal use of undegraded‐feed soluble protein and accuracy of the estimations of the nutrient content in ruminal bacteria

BACKGROUND The possible escape from the rumen of undegraded‐feed soluble proteins (SP) was investigated using nitrogen‐15 (15N) infusions (25 mg) in three rumen and duodenum cannulated wethers. Animals were fed three isoproteic diets differing in SP content and including protein concentrates either untreated (control) or treated with solutions of either malic acid (MHT) or orthophosphoric acid (OHT) and heat. RESULTS Compared with control, MHT and OHT diets reduced ruminal concentrations of ammonia‐nitrogen (NH3‐N) by 35.9% (P = 0.007), non‐ammonia nitrogen (NAN) by 36.8% (P = 0.007), and SP‐nitrogen (SP‐N) by 45.2% (P = 0.072) over the post‐feeding period. Both NAN and SP‐N were lower (P ≤ 0.040) for OHT than for MHT diet. The 15N enrichment of NAN and SP‐N did not vary either among diets or with time, and both values were closely related (R2 = 0.965; P