The importance of the form of nitrogen on microbial protein synthesis in the rumen of cattle receiving grass silage and continuous intrarumen infusions of sucrose.
1. In a 4 x 4 Latin square design experiment, four cattle were given grass silage in two meals per d to satisfy maintenance energy requirements. In addition, sucrose (170 g/kg silage dry matter (DM] was infused intraruminally at a constant rate with no nitrogen supplementation; with the infusion intraruminally of either casein (23 g/kg silage DM) or urea (8 g/kg silage DM); or with soya-bean meal (64 g/kg silage DM) fed in two equal portions. 2. Samples of duodenal digesta representative of a 24 h period were obtained using chromium-EDTA and ytterbium acetate for flow estimation and 35S as a marker of microbial N entering the small intestine. Samples of rumen fluid were also taken for estimation of rumen pH and concentrations of ammonia-N and volatile fatty acids. Estimates of apparent organic matter (OM) and N digestibility and of the rates of silage DM and N disappearance from porous synthetic-fibre bags incubated in the rumen were also made. 3. The N supplements had no significant effects on rumen pH, concentrations of volatile fatty acids, their molar proportions or the disappearance of DM or N from porous synthetic-fibre bags. N supplementation increased rumen ammonia-N concentrations (urea, P less than 0.05; casein, soya-bean meal, not significant). 4. N supplementation had no significant effects on the digestion of OM, acid-detergent fibre or soluble carbohydrate. 5. Infusion of casein increased the quantities of total non-ammonia-N (not significant) and microbial N (P less than 0.05) entering the small intestine daily and the efficiency of rumen microbial N synthesis (not significant).(ABSTRACT TRUNCATED AT 250 WORDS)
Rooke
J A
JA
Department of Agricultural Biochemistry and Nutrition, University of Newcastle upon Tyne.
Armstrong
D G
DG
D000821:Animal Feed; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis*; D002364:Caseins / Q000008:administration & dosage; D002417:Cattle; D004032:Diet; D005260:Female; D009584:Nitrogen / Q000502:physiology*; D012417:Rumen / Q000378:metabolism*; D012820:Silage; D013025:Glycine max; D013395:Sucrose / Q000008:administration & dosage*
D001426:Bacterial Proteins; D002364:Caseins; D013395:Sucrose; D009584:Nitrogen