title: Effective nitrogen preservation during urine collection from Holstein heifers fed diets with high or low protein content.
abstract: Six Holstein heifers (body weight=535-625 kg) fed a total mixed ration containing either high protein (13.4%) or low protein (9.0%) were used to evaluate the effect of 3 urine collection methods (chilled, acidified before collection, or acidified after 6h of collection) on urinary N preservation. In a 2-period crossover design, 16-d diet adjustment stages preceded five 24-h collections. Urinary catheters were inserted 1 d before the collection periods. Urine collection tubes were configured to split urine to 3 collection containers: 1 acidified with 6 N HCl before collection at a rate calculated to reduce pH to below 2, 1 acidified every 6h during collection to pH below 2, and 1 located in a large cooler of ice. Collection method did not affect urinary concentration of N or urine urea-N (9.2+/-0.9 g/L and 6.58+/-0.9 g/L, respectively) or urinary excretion of N or urea-N (82+/-3.8 g/d and 59.5+/-3.8 g/d, respectively). These 3 collection methods are equally effective in preserving N during urine collection, but the "chilled immediately" approach may be useful for studies focused on ammonia emission. Urinary and fecal N excretion were significantly different across collection days; fecal N was more highly variable than urinary N. Intake and apparent N digestibility decreased during the collection week, and excretion of urinary and fecal N increased, particularly on d 5. (Stable rectal temperatures suggested no urinary infections.) Improvements in total collection methodology will support continued progress in the understanding of livestock N utilization and post-excretion changes in manure N.
authors.affiliation: Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA. knowlton@vt.edu
authors.forename: K F
authors.initials: KF
authors.lastname: Knowlton
authors.forename: M L
authors.initials: ML
authors.lastname: McGilliard
authors.forename: Z
authors.initials: Z
authors.lastname: Zhao
authors.forename: K G
authors.initials: KG
authors.lastname: Hall
authors.forename: W
authors.initials: W
authors.lastname: Mims
authors.forename: M D
authors.initials: MD
authors.lastname: Hanigan
mesh_terms: D000818:Animals; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D018592:Cross-Over Studies; D003612:Dairying / Q000379:methods*; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D005243:Feces / Q000737:chemistry; D005260:Female; D009584:Nitrogen / Q000652:urine*; D011247:Pregnancy; D011309:Preservation, Biological / Q000662:veterinary; D013997:Time Factors
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen