title: Compartmental modeling with nitrogen-15 to determine effects of degree of fat saturation on intraruminal N recycling.
abstract: Two- and three-compartment models were developed to describe N kinetics within the rumen using three Holstein heifers and one nonlactating Holstein cow fitted with ruminal and duodenal cannulas. A 4 x 4 Latin square design included a control diet containing no supplemental fat and diets containing 4.85% of diet dry matter as partially hydrogenated tallow (iodine value = 13), tallow (iodine value = 51), or animal-vegetable fat (iodine value = 110). Effects of fat on intraruminal N recycling and relationships between intraruminal N recycling and ruminal protozoa concentration or the efficiency of microbial protein synthesis were determined. A pulse dose of 15(NH4)2SO4 was introduced into the ruminal NH3 N pool, and samples were taken over time from the ruminal NH3 N and nonammonia N pools. For the three-compartment model, precipitates of nonammonia N after trichloroacetic acid and ethanol extraction were defined as slowly turning over nonammonia N; rapidly turning over nonammonia N was determined by difference. Curves of 15N enrichment were fit to models with two (NH3 N and nonammonia N) or three (NH3 N, rapidly turning over nonammonia N, and slowly turning over nonammonia N) compartments using the software SAAM II. Because the three-compartment model did not remove a small systematic bias or improve the fit of the data, the two-compartment model was used to provide measurements of intraruminal N recycling. Intraruminal NH3 N recycling (45% for control) decreased linearly as fat unsaturation increased (50.2, 43.0, and 41.7% for partially hydrogenated tallow, tallow, and animal-vegetable fat, respectively). Intraruminal nitrogen recycling was not correlated with efficiency of microbial protein synthesis or ruminal protozoa counts.
authors.affiliation: Department of Animal Sciences, The Ohio State University, Columbus 43210, USA.
authors.forename: B S
authors.initials: BS
authors.lastname: Oldick
authors.forename: J L
authors.initials: JL
authors.lastname: Firkins
authors.forename: R A
authors.initials: RA
authors.lastname: Kohn
mesh_terms: D000645:Ammonium Sulfate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004041:Dietary Fats / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D016018:Least-Squares Analysis; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000378:metabolism; D012417:Rumen / Q000378:metabolism*
chemical_list: D004041:Dietary Fats; D005231:Fatty Acids, Unsaturated; D009587:Nitrogen Isotopes; D009584:Nitrogen; D000645:Ammonium Sulfate