Comparison of kinetics of in vitro N-NH3 production and rumen degradation of N of coated urea, urea and agro industrial by products

Kinetics of N-NH3 production in vitro, and degradation of N in rumen of urea coated with biodegradable polymers (coated urea), urea, sunflower meal, soybean meal, gluten meal, and dehydrated brewers´grains, were compared. Ammonia production was evaluated by incubating (ruminal fluid + nutritive solution) samples during 0, 0.5, 1, 2, 4, 6, 8, 12 y 24 h. Ruminal degradation was studied in situ, incubating (2, 4, 12, 24, 48 y 72 h; two periods) bags in two fistulated wethers. Urea and coated urea showed the greatest (P <0,001) N-NH3 , registering coated urea lower (P <0,05) values up to 12 h, which were similar (P = 0,17) at 24h. In rumen, coated urea appeared with the greatest (P <0,001) N degradation rate (kd) (3,62 h-1), disappearing 95% of total N at first hour of incubation, results that were different from expected. Washing procedure (mechanical) and drying temperature (60º C) of bags, may have modified urea cover; then, DM disappearance of coated urea incubated in situ with bags machine or hand washed, and dried at 39 and 60o C was evaluated. Mechanical procedure resulted in greater (P < 0,001) DM disappearance than manual procedure, with a tendency (P = 0,07) to lower DM loss when drying at 39º C. Once again, coated urea incubated in situ (manual washed and drying at 39º C), registered lower (P <0,001) kd (1,59 h-1) than previously, and maximum N disappearance of N (91%) 8 h post-incubation. In coated urea N release in rumen was slower than in urea but faster than in byproducts.