title: Effects of ruminal casein and glucose on forage digestion and urea kinetics in beef cattle.
abstract: Effects of supplemental glucose and degradable intake protein on nutrient digestion and urea kinetics in steers (Bos taurus) given ad libitum access to prairie hay (4.7% CP) were quantified. Six ruminally and duodenally cannulated steers (initial BW 391 kg) were used in a 4 × 4 Latin square with 2 extra steers. Treatments were arranged as a 2 × 2 factorial and included 0 or 1.2 kg of glucose and 240 or 480 g of casein dosed ruminally once daily. Each period included 9 d for adaptation, 4 d for total fecal and urine collections, and 1 d for ruminal and duodenal sampling. Jugular infusion of (15)N(15)N-urea with measurement of enrichment in urine was used to measure urea kinetics. Glucose reduced forage intake by 18% (P < 0.01), but casein did not affect forage intake (P = 0.69). Glucose depressed (P < 0.01) total tract NDF digestion. Glucose supplementation decreased ruminal pH 2 h after dosing, but the effect was negligible by 6 h (treatment × time; P = 0.01). Providing additional casein increased the ruminal concentration of NH(3), but the increase was less when glucose was supplemented (casein × glucose; P < 0.01). Plasma urea-N was increased (P < 0.01) by additional casein but was reduced (P < 0.01) by glucose. Microbial N flow to the duodenum and retained N increased (P ≤ 0.01) as casein increased, but neither was affected by glucose supplementation. Urea-N entry rate increased (P = 0.03) 50% with increasing casein. Urinary urea-N excretion increased (P < 0.01) as casein increased. The proportion of urea production that was recycled to the gut decreased (P < 0.01) as casein increased. Glucose supplementation decreased (P < 0.01) urinary urea excretion but did not change (P ≥ 0.70) urea production or recycling. The amount of urea-N transferred to the gut and captured by ruminal microbes was less for steers receiving 480 g/d casein with no glucose than for the other 3 treatments (casein × glucose interaction, P = 0.05), which can be attributed to an excess of ruminally available N provided directly to the microbes from the supplement. Overall, the provision of supplemental glucose decreased forage intake and digestibility. Increasing supplemental casein from 240 to 480 g/d increased urea production but decreased the proportion of urea-N recycled to the gut.
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; D004435:Eating; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D009584:Nitrogen / Q000097:blood / Q000172:deficiency / Q000378:metabolism*; D012417:Rumen / Q000502:physiology*; D014508:Urea / Q000097:blood / Q000378:metabolism* / Q000652:urine
chemical_list: D001786:Blood Glucose; D002364:Caseins; D000641:Ammonia; D014508:Urea; D005947:Glucose; D009584:Nitrogen