The influence of timing and the addition of urea to supplements containing DL-methionine on ruminal fermentation and cow weight change in beef cows.

A study was conducted to determine an optimal time for supplementation of DL-methionine in relation to time of forage intake by mature British breed-type crossbred cows, and two other experiments were conducted to determine whether ruminal ammonia concentration limited changes in disappearance rates in situ and ruminal functions caused by supplements containing DL-methionine. Experiments 1 and 2 used 4 x 4 Latin square designs with four cows in each experiment. Treatments in Exp. 1 were no supplement (CON), DL-methionine at feeding (0800), DL-methionine 4 h after feeding (1200), and DL-methionine 7 h after feeding (1500). Treatments in Exp. 2 were .5 kg of beet pulp (CON), .5 kg of beet pulp plus 16.5 g of DL-methionine (MET), .5 kg of beet pulp plus 16.5 g of DL-methionine and 55 g of urea (METU), and .4 kg of soybean (SOY). Experiment 3 was conducted in a 326-ha pasture with treatments of no supplement (CON), .5 kg of beet pulp plus 12.5 g of DL-methionine and 30 g of urea (METU), and .4 of kg soybean meal (SOY). In Exp. 1, in situ NDF disappearance rates of cows supplemented at 1200 and 1500 were greater (P less than .01) than those of cows supplemented at 0800. In Exp. 2, ruminal ammonia concentration was greatest (P less than .001) for METU (5.2 mg/dl) and least for CON (1.5 mg/dl). Disappearance rates in situ for DM differed (P less than .01) among treatments; METU was similar (P greater than .2) to SOY but faster (P less than .01) than MET. Disappearance rates of NDF were greatest (P less than .001) for METU-supplemented cows. In Exp. 3, DM and NDF disappearance rates were faster (P less than .10) for SOY than for METU. Cow BW change was positive for METU and SOY, and decrease in condition score was least (P less than .10) for METU- and SOY-treated cows. These studies indicate favorable ruminal responses to DL-methionine supplementation; however, the response depended on time of supplementation and ruminal ammonia concentration.

Substitution of DL-methionine for soybean meal as a winter supplement for gestating cows grazing native range.

A winter grazing study was conducted to determine whether DL-methionine could replace soybean meal as a N supplement for gestating beef cows. During two winters (Trial 1, n = 51; Trial 2, n = 60), crossbred beef cows grazed native foothill range. Three treatment groups were supplemented with either none (CON), DL-methionine (7.5 g Trial 1 and 9 g Trial 2) in .5 kg beet pulp carrier (BPM) or .4 kg soybean meal (SBM). Cows were supplemented individually every other day. Small differences were noted in cow BW, condition score and blood metabolites. Unsupplemented cows lost the greatest amount of BW (P less than .01) in both trials and lost more (P less than .05) condition during Trial 1 than cows fed BPM or SBM supplements. Blood samples were obtained on two consecutive days during each trial (45 d and 25 d prepartum) and analyzed for blood urea N, total bilirubin, creatinine, albumin, total protein and cholesterol. A treatment x day preparatum interaction (P less than .05) was noted for blood urea. Blood urea nitrogen declined as gestation length increased for CON and SBM cows, but blood urea of BPM-supplemented cows remained low and unchanged. In situ forage digestion was measured in 12 ruminally cannulated cows (four/treatment). In both trials, in situ rate of NDF disappearance was greater (P less than .05) for SBM than for BPM. In Trial 2, a treatment x sampling hour interaction was detected for purine concentration of whole ruminal contents; SBM maintained greater purine concentrations throughout the 48-h supplementation cycle than BPM did. Principal component analysis suggested that ruminal ammonia limited the microbial growth response to DL-methionine. Therefore, alternate-day supplementation of DL-methionine plus beet pulp did not effectively substitute for soybean meal in these trials.