Evaluation of the effects of adding conventional urea and slow release urea to diets containing molasses on microbial fermentation by gas production method

This experiment was conducted to investigate the effects of source and level of non-protein nitrogen, as well as the level of molasses added to high concentrate diets on gas production parameters. A completely randomized design with factorial (2×2×3) arrangement of 12 treatments with 5 replications was used. Factors were two types of non-protein nitrogen sources, common urea and slow-release urea (Nitroza) each in two levels (0.8 and 1.6%) and (0.9 and 1.8%) on dry matter basis of ration respectively, and molasses at three levels (0, 10 and 20%). With increasing of molasses, the amounts of cumulative gas production up to 24 hours of incubation, metabolisable energy, truly organic matter digestibility, organic matter digestibility and short chain fatty acids, increased (p < 0.05). Cumulative gas production was not affected by non-protein nitrogen source and its levels. Truly organic matter digestibility was higher in diets containing slow-release urea than conventional urea, but in other parameters there was no difference between the two non-protein nitrogen sources. In general, the results showed that the rate of ammonia release from conventional and slow release urea in the culture medium does not have a significant effect on in vitro fermentation, but adding 20% molasses on dry matter basis of ration, improved the gas production parameters.