title: Effects of supplemental energy and protein on forage digestion and urea kinetics in growing beef cattle.
abstract: Effects of supplemental energy sources on nutrient digestion and urea kinetics at 2 levels of degradable intake protein were evaluated in cattle (Bos taurus). Six ruminally and duodenally cannulated steers (208 ± 17 kg) were used in a 6 × 6 Latin square with treatments arranged as a 3 × 2 factorial. Energy treatments included a control, 600 g glucose dosed ruminally once daily, and 480 g VFA infused ruminally over 8 h daily. Casein (120 or 240 g) was dosed ruminally once daily. Steers had ad libitum access to prairie hay (5.8% CP). Jugular infusion of (15)N(15)N-urea with measurement of enrichment in urine was used to measure urea kinetics. Infusing VFA decreased (P < 0.01) forage intake by 27%. Supplementing glucose decreased (P < 0.01) total tract NDF digestibility and tended to decrease ruminal NDF digestibility; depressions in response to glucose tended to be greater at the lower level of casein. Increasing casein decreased (P < 0.02) ruminal pH. Infusing VFA decreased pH only during infusions, whereas glucose decreased pH 2 h after dosing. Ruminal concentrations of NH(3), acetate, and propionate decreased and butyrate concentration increased when glucose was supplemented. Increasing casein supplementation increased (P < 0.01) ruminal concentrations of NH(3), acetate, and propionate. Supplemental energy decreased (P = 0.03) plasma urea-N concentration, but casein level did not affect it (P = 0.16). Microbial N flow was greater (P < 0.04) for 240 than for 120 g/d casein but was not affected by supplemental energy (P = 0.23). Urea-N entry rate and gut entry of urea-N were not affected (P ≥ 0.12) by supplemental energy or casein, but the proportion of urea production that was recycled to the gut was less (P = 0.01) when 240 g/d rather than 120 g/d casein was provided. Compared with VFA, glucose tended (P = 0.07) to increase the proportion of urea-N entry rate that was recycled to the gut. Supplementation with glucose led to more (P = 0.01) microbial uptake of recycled urea than did supplementation with VFA. Urea recycling did not differ greatly among treatments despite impacts on ruminal pH and NH(3) and on plasma urea-N that were expected to alter urea transport across ruminal epithelium. Lack of treatment effects on urea production indicate that the complete diets did not provide excessive amounts of N and that increases of intestinally available AA were used efficiently by cattle for protein deposition.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Bailey
authors.forename: E C
authors.initials: EC
authors.lastname: Titgemeyer
authors.forename: K C
authors.initials: KC
authors.lastname: Olson
authors.forename: D W
authors.initials: DW
authors.lastname: Brake
authors.forename: M L
authors.initials: ML
authors.lastname: Jones
authors.forename: D E
authors.initials: DE
authors.lastname: Anderson
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D002364:Caseins / Q000008:administration & dosage / Q000378:metabolism; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D019587:Dietary Supplements / Q000032:analysis; D004063:Digestion; D004305:Dose-Response Relationship, Drug; D002149:Energy Intake; D005232:Fatty Acids, Volatile / Q000008:administration & dosage / Q000378:metabolism*; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D012417:Rumen / Q000502:physiology; D014508:Urea / Q000097:blood / Q000378:metabolism* / Q000652:urine
chemical_list: D001786:Blood Glucose; D002364:Caseins; D005232:Fatty Acids, Volatile; D000641:Ammonia; D014508:Urea; D005947:Glucose