SUPPLEMENTAL METHIONINE AND TIME OF SUPPLEMENTATION EFFECTS ON RUMINAL FERMENTATION, DIGESTA KINETICS, AND IN-SITU DRY-MATTER AND NEUTRAL DETERGENT FIBER DISAPPEARANCE IN CATTLE

Two experiments were conducted to study the effects of methionine supp lementation on ruminal fermentation and digesta kinetics. In Exp. 1, n ine ruminally cannulated beef heifers (average initial BW = 527 kg) in a crossover design were fed low-quality grass hay and cottonseed meal with or without 11.4 g of supplemental methionine (polysaccharide-coa ted). Particulate and fluid kinetics, rate of DM and NDF disappearance , ruminal VFA and NH3 N concentrations, and pH were not altered (P > . 10) by supplemental methionine; however, ruminal purine concentration was greater (P < .05) in methionine-supplemented heifers than in unsup plemented heifers. In Exp. 2, 12 ruminally cannulated Holstein steers (average initial BW = 622 kg) grazing a fescue pasture were allotted t o one of three groups: no supplemental methionine (CON) or 11.4 g of s upplemental methionine fed at 0700 (AM) or at 1200 (PM). Forage intake , particulate kinetics, ruminal fluid kinetics, pH, VFA, and NH3 N con centrations were not altered (P > .10) by supplemental methionine or s upplementation time. In situ rate of DM and NDF disappearance was grea ter (P < .05) in supplemented steers than in CON steers; AM steers exh ibited faster (P < .05) rates than PM steers. Overall, methionine supp lementation of low-quality forage increased ruminal purine concentrati on but did not alter in situ fermentation or digesta passage, whereas supplementation at 0700, but not at 1200, of steers grazing fescue for age increased rate of NDF fermentation.