The potential of isobutyraldehyde monourea (propanal, 2-methyl-monourea) as a nonprotein nitrogen source for ruminant animals

Abstract

Experiments were earned out with sheep and in vitro to evaluate isobutyraldehyde monourea (IBMU; propanal-2-methyl-monourea) as a slow-release nitrogen source for ruminant animals. Examination of the compound for carbon, hydrogen, and nitrogen composition and infrared, NMR and mass spectral analyses indicated that IBMU was present in significant amounts. Ten sheep were randomly assigned to diets containing bromegrass hay and corn grain and the following nitrogen supplementation treatments: (1) control, (2) urea, (3) soybean meal, (4) canola meal and (5) IBMU, with the protein supplements providing approximately 25% of the nitrogen intake. Similar treatments were also prepared and evaluated in vitro, with the exception that wheat straw rather than bromegrass hay was used in the incubation. The digestibility of nitrogen in the ration containing IBMU was higher (P < 0.05) than its digestibility in the other rations when measurements were conducted with sheep over three 14-d periods. No differences in dry matter (DM) or energy digestibility were detected between the different treatments. The digestible energy content of IBMU was estimated to be greater than 21 MJ kg−1. The digestibilities of DM in vitro after 2, 4, 8, 12, 24, 48 and 72 h of incubation were not influenced by the presence of IBMU. No influence of nitrogen supplementation on nitrogen balance was observed, probably because of the high protein content of the control ration (10.6%). IBMU exhibited the characteristics of an ideal slow-release nonprotein nitrogen supplement, since concentrations of rumen ammonia nitrogen did not vary from 0 to 8 h after feeding and ammonia concentrations were higher (P < 0.05) both before feeding and 8 h after feeding when IBMU was fed than when any of the other supplements were fed. The concentration of isobutyric acid averaged 2.6-fold higher when IBMU was fed than when canola meal or soybean meal was fed, confirming that most of the compound was degraded in the rumen. Sheep fed IBMU had lower concentrations of acetic, propionic and butyric acid in the rumen than those fed natural protein supplements. It was unclear whether the decrease in VFA concentration was positive or negative in terms of nutritional value. It was concluded that IBMU exhibited some ideal characteristics for a nonprotein nitrogen supplement for ruminant animals because it was degraded at an optimum rate in the rumen and provided rumen microflora with isobutyric acid. Further experimentation is warranted to determine its usefulness when nitrogen-deficient diets are fed to ruminant animals. Key words: Nonprotein nitrogen, isobutyric acid, isobutyraldehyde, slow-release, isobutyraldehyde monourea, propanal-2-methyl-monourea