title: Effect of ruminal vs postruminal administration of degradable protein on utilization of low-quality forage by beef steers.
abstract: An experiment was designed to determine the effects of ruminal and postruminal infusions of ruminally degradable protein (casein) on intake and digestion of low-quality hay by beef steers. Twelve ruminally fistulated Angus x Hereford steers (initial BW = 563 kg) were blocked by weight and assigned to one of three treatments: control (C; hay only) or hay plus ruminal (R) or postruminal (P) infusion of 400 g/d of sodium caseinate. The trial consisted of five periods: 1) 10-d adaptation to the hay diet; 2) 7-d measurement of hay intake (without infusions); 3) 10-d adaptation to protein infusion treatments (intake measurements continued); 4) 7-d measurement of hay intake and digestibility (infusions continued); and 5) 3-d ruminal sampling period (infusions continued). Steers were given ad libitum access to tallgrass-prairie hay (3.4% CP, 76.6% NDF) throughout the study. Casein was administered once daily before feeding, either directly into the rumen or via anchored infusion lines into the abomasum. Hay intake was increased by supplementation (P < 0.01). Ruminal infusion elicited a greater (P = 0.04) increase in hay intake than postruminal infusion. Intake tended (P = 0.11) to be lower in period 4 than in period 2 for control steers but was greater in period 4 than in period 2 (P < or = 0.03) for both R and P steers. The increase in intake between periods 2 and 4 was greater for R than for P steers (P = 0.03). Supplementation improved diet OM digestion (P = 0.04) but not NDF digestion (P = 0.18); however, greater relative error for NDF digestion may have limited the ability to elucidate significant treatment effects. There were no differences in either OM digestion (P = 0.42) or NDF digestion (P = 0.35) between R and P steers. Plasma urea N at 0 and 3 h after feeding on the last day of the experiment was lower (P = 0.05) for C than for R and P steers, but no difference (P = 0.48) was evident between R and P steers. Ruminal ammonia N levels also were increased by supplementation (P < 0.01), with a much larger increase for R than for P steers (P < 0.01). Total VFA concentrations were not affected (P = 0.21) by treatment, but R steers exhibited lower proportions of acetate and higher proportions of isobutyrate, valerate, and isovalerate than P steers (P < 0.01). In conclusion, ruminal and postruminal infusion of a degradable protein source improved forage utilization, although the response in forage OM intake and total digestible OM intake was greater for ruminal infusion than for postruminal infusion.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Bandyk
authors.forename: R C
authors.initials: RC
authors.lastname: Cochran
authors.forename: T A
authors.initials: TA
authors.lastname: Wickersham
authors.forename: E C
authors.initials: EC
authors.lastname: Titgemeyer
authors.forename: C G
authors.initials: CG
authors.lastname: Farmer
authors.forename: J J
authors.initials: JJ
authors.lastname: Higgins
mesh_terms: D000821:Animal Feed / Q000592:standards; D000818:Animals; D001806:Blood Urea Nitrogen; D002364:Caseins / Q000008:administration & dosage / Q000494:pharmacology; D002417:Cattle / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D019587:Dietary Supplements; D004063:Digestion; D004435:Eating; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D006109:Poaceae; D012417:Rumen / Q000502:physiology
chemical_list: D002364:Caseins; D004044:Dietary Proteins; D009584:Nitrogen