| Popis: |
Two dry cows fitted with a re-entrant cannula before the pancreatic and biliary ducts were used in twenty 72-h experiments for the purpose of measuring the flow and composition of the duodenal digesta. The rations were maize silage alone (control) or the same forage supplemented with increasing amounts of soya bean meal, urea, isobutylidene diurea (IBDU) or starea. For crude protein concentrations below 8.8% in ingested dry matter, all N supplements gave equivalent results. Above this point, the substitution of urea or starea for soya bean meal decreased the total and non-ammonia N flows in the duodenum. But the highest values were obtained with IBDU. However, when compared with soya bean meal, the increase noted with IBDU was mainly due to the high ammonia contribution. The substitution of non-protein nitrogen for soya bean meal improved the efficiency of bacterial protein synthesis in the rumen. Nevertheless, the duodenal flow of bacterial N rapidly levelled off at crude protein concentrations above 9–10% in the ingested dry matter when increasing amounts of urea or starea were added to the maize silage. The association of urea with fermentable carbohydrates (starea) thus did not improve its conversion into bacterial protein in the rumen. However, a more efficient bacterial protein synthesis was noted with IBDU. The protozoal + undegraded dietary N fraction was greatest with soya bean meal. The association of maize silage with starea or urea tended to decrease this N fraction as compared with the unsupplemented ration, suggesting a higher proteolysis in the rumen under these circumstances. |
