Edmonton' Atberta'Mathison, G. W., Soofi-Siawash, R. and Worsley, M. 1994. The potential of isobutyraldglVd9-1o-1o.urya (propanal' 2-methylmonogrea, as a nonprotein ttit"og.n source foi ruminant animals. Can. J. Anim. Sci. 74: 665-6'74. Experiments. were carried out with sheep and in vitro to evalu-ate isobutyraldehyde monourea (IBMU; propanal-2-methyl-monourea) as a slorp_-release nit-ro-gen source for ruminant animals. Examination of the co-pound for carbon, nlarogen, and nitrogen composition and infrared' NMR and mass spectral analyses indicated that IBMU was present in significant ainounts. Ten sheep were rar-rdolnlY assigrred to diets containing bromegrass tray anO corn grain and the following nitrogen Jupptementation treatnents: (1) control, (2) urea' (3) soybean meal' (4) cfroh me."al and (5) fslvlU, #ittr ttt. protein supplelments-providiirg approximately 25% of the nitrogen intake. Similar treatrnents were also prepared and evaluated in vitro, with thetiception that ryheat siqw rathgl than br.omggrass.hay was used in the incubation.fne algesiiUiiity of nilrogen in the ration containing IBMU *., higher (P < 0.05) than its digesliqqiry in the other ratiojls when measurements were cond"ucted with sheep over ttuei 14-d 130 to 185'C (10"C min-'). A helium carrier gas was used.Samples for ammonia were also taken at the same time as VFA samples and stored at -20'C for analysis. Baetz et al. (1979) reported that rumen ammonia concentrations in frozen samples were stable for at least 3 wk and all samples were analyzed within this period. Rumen ammonia levels were analyzed using the colorimetric technique described by Fawcett and Scott (1960).In Vitro Measurements DM disappearance and ammonia accumulation were measured by in vitro incubations. The mixture of substrates was sirnilar to that used in the sheep feeding trial, with the exception that wheat straw (2.6% crude protein) was substituted for the brome hay to reduce the N content of the incubated substrates. Approximately 0.3 g DM was included in each incubation tube, and incubations were carried out according to the procedure of Marten and Barnes (1979). Control tubes and those with supplemental nitrogen thus contained approximately 2.4 and 3.5 mg N, respectively, with 40% of the total N arising from the supplemental N source. Incubations were conducted at 39"C in 50-mL plastic tubes containing buffer solution (McDougall 1948)

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