Effect of coated urea and monensin on rumen metabolism of Nellore cows fed low-quality forage-based diet

This study investigated the effect of coated urea supplementation associated with monensin on rumen metabolism and fermentation, in cattle consuming a low-quality forage-based diet. Eight ruminally cannulated Nellore cows consuming Brachiaria brizantha cv. Marandu hay were randomly assessed to two 4 x 4 Latin square design, in a 2 x 4 factorial arrangement, with a factorial treatment arrangement with the factors: (i) urea source: (CON) no urea, (URE) common urea, (PCU) polymer-coated urea and (LCU) lipid-coated urea; (ii) monensin: (MON) addition of monensin in the diet; and (NM) no addition of monensin in the diet. Ruminal NH3-N concentration was affected by urea source and there was an interaction between time and the urea source. Rumen acetate molar concentration was lower, while rumen propionate was greater for URE compared to coated urea. The total tract apparent digestibility of crude protein (CP) and non-protein nitrogen (NPN) were greater for URE compared to coated urea treatments and for LCU compared to PCU. Animals fed URE had greater urea excretion compared to coated urea. In conclusion, coated urea generates a lower ammonia peak; however, both coated urea did not promote total nitrogen release. No synergy was observed with the combination of urea and monensin.