Effect of methionine addition to a urea-grain supplement on intake and digestibility of mature, dormant grasses and performance of cows grazing winter range

A digestibility trial involving 20 Hampshire ram lambs and a 2-yr grazing study using 103 mature crossbred cows were conducted to determine the effects of methionine addition to a urea-grain supplement on intake and digestibility of dormant range grasses and on cow performance. In each trial, four treatment groups were supplemented with either a urea-grain control (CON), urea-grain plus methionine (MET, 3.3% DL-methionine), urea-grain plus inorganic sulfur (SUL, 3.0% sodium sulfate), or soybean meal (SBM). Supplements were designed to provide 45 and 360 g of CP.animal-1.d-1 (lambs and cows, respectively) and were balanced for ME, Ca, P, and K. Lambs had ad libitum access to mature prairie hay, whereas cows grazed dormant winter range from mid-November until mid-February. For the grazing study, forage OM intake (OMI) was determined in late November and in late January by the fecal output/indigestibility ratio technique. Controlled-release chromic oxide boluses were used as an external marker to estimate fecal output, and acid insoluble ash was used as an internal marker to predict OM digestibility (OMD). Mean daily DMI of mature prairie hay was 1,057 g/lamb and was not affected by supplementation. Apparent DM, NDF, and ADF digestibilities and N biological value did not differ (P > .10) among treatments. Nitrogen digestibility was increased (P = .06) for lambs fed the MET or SUL compared with CON. For the winter grazing study, cow weight gains for SBM tended (P < .10) to be greater than those for MET, SUL, and CON; weight changes were greater (P < .0 5) for SUL than for MET. Differences in OMI among treatment groups were not detected (P > .10). There was a supplement treatment X grazing period interaction (P < .01) for OMD. In late November and January, OMD was greater (P < .01) by cows fed SBM than by cows fed a urea supplement. In late January, OMD was greater (P < .01) by cows fed SUL than by those fed MET. Methionine addition to a urea-grain supplement did not increase grass digestibility or performance by cows grazing dormant winter range.