title: Compartmental flux and in situ methods underestimate total feed nitrogen as judged by the omasal sampling method due to ignoring soluble feed nitrogen flow.
abstract: The objective of the present study was to estimate ruminal feed N outflow in lactating cows using the omasal sampling, compartmental flux or in situ method. A total of five ruminally fistulated Finnish Ayrshire dairy cows were used in a 5 × 5 Latin square study with 21 d periods. Experimental silages of grass or red clover harvested at two stages of maturity in addition to a supplement of 9·0 kg concentrate/d were fed to the cows. In vivo omasal N flow was determined using the omasal sampling technique. Ruminal in situ N flow was calculated from N intake and degradability (38 μm nylon bags). The samples of ruminal contents and faeces were divided into seven particle-size fractions by wet sieving; the concentrations of indigestible neutral-detergent fibre and N were used to calculate N flow in the compartmental flux method. In vivo omasal N flow was greater for the red clover silage diets than for the grass silage diets. The N flow calculated using the compartmental flux technique and that calculated using the in situ technique were highly correlated, but both were less than and poorly correlated with the in vivo N flow. In both in situ and compartmental flux techniques, forage maturity increased the particle-associated N flow, with the increase being significantly greater for the red clover diets than for the grass silage diets. In conclusion, the compartmental flux and in situ methods described the N flow associated with the particle fractions rather than the total ruminal outflow of feed N.
authors: Department of Agriculture for Northern Sweden, Swedish University of Agricultural Sciences, S-90183 Umeå, Sweden.
authors: Pekka
authors: P
authors: Huhtanen
authors: MTT Agrifood Research Finland, Animal Production Research, FI-31600 Jokioinen, Finland.
authors: Alireza
authors: A
authors: Bayat
authors: Department of Agriculture for Northern Sweden, Swedish University of Agricultural Sciences, S-90183 Umeå, Sweden.
authors: Sophie J
authors: SJ
authors: Krizsan
authors: Department of Agricultural Sciences, University of Helsinki, PO Box 28, FI-00014 University of Helsinki, Finland.
authors: Aila
authors: A
authors: Vanhatalo
mesh_terms: D000818:Animals; D017849:Animals, Inbred Strains; D002417:Cattle; D003612:Dairying; D004032:Diet / Q000662:veterinary*; D004063:Digestion; D005260:Female; D005387:Finland; D005747:Gastric Fistula / Q000662:veterinary; D005766:Gastrointestinal Contents / Q000737:chemistry*; D007774:Lactation / Q000378:metabolism; D008954:Models, Biological; D009574:Nitro Compounds / Q000008:administration & dosage / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D009584:Nitrogen / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism*; D017672:Nitrogen Compounds / Q000008:administration & dosage / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D009851:Omasum / Q000378:metabolism*; D010316:Particle Size; D006109:Poaceae / Q000737:chemistry / Q000254:growth & development; D015203:Reproducibility of Results; D012820:Silage / Q000032:analysis*; D012995:Solubility; D029921:Trifolium / Q000737:chemistry / Q000254:growth & development
chemical_list: D009574:Nitro Compounds; D017672:Nitrogen Compounds; D009584:Nitrogen