title: The effects of crude protein concentration and slow release urea on nitrogen metabolism in Holstein steers.
abstract: This experiment was conducted to determine the effects of slow release urea (SRU) and its interaction with crude protein (CP) level in the diet on N metabolism in Holstein steers. Eight rumen-cannulated Holstein steers (body weight 265 ± 18 kg) were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial treatment structure. Treatment factors were the CP level in the diet, 10.9% versus 12.1% CP, and the non-protein nitrogen source used, urea versus SRU. Total collection of urine and faeces for 7 days allowed the estimation of N retention and diet digestibility. In addition, blood and rumen sampling allowed estimation of rumen fermentation and blood N profiles. Decreasing CP intake from 12.1% to 10.9% reduced urinary N output, but also reduced diet digestibility and N retention. When compared to urea, SRU did not alter N retention, but reduced ruminal ammonia and plasma urea concentrations. Although SRU did not improve N retention at either CP level, rumen ammonia and plasma urea concentrations were reduced, which may indicate that SRU may carry a lower risk for toxicity when compared to urea when fed at higher dietary concentrations.
authors.affiliation: Department of Animal and Food Sciences , University of Kentucky , Lexington , KY , USA.
authors.forename: Vaughn B
authors.initials: VB
authors.lastname: Holder
authors.forename: Samer W
authors.initials: SW
authors.lastname: El-Kadi
authors.forename: Juan M
authors.initials: JM
authors.lastname: Tricarico
authors.forename: Eric S
authors.initials: ES
authors.lastname: Vanzant
authors.forename: Kyle R
authors.initials: KR
authors.lastname: McLeod
authors.forename: David L
authors.initials: DL
authors.lastname: Harmon
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000378:metabolism*; D018592:Cross-Over Studies; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000494:pharmacology*; D005766:Gastrointestinal Contents / Q000737:chemistry; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism; D014508:Urea / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D004044:Dietary Proteins; D014508:Urea; D009584:Nitrogen