Effects of feeding urea-treated triticale and oat grain mixtures on ruminal fermentation, microbial population, and milk production performance of midlactation dairy cows

The starch content of triticale and oat grains provides much of their readily available energy. Synchronizing energy and nitrogen in the rumen is important in optimizing profitability; for this reason, ammonia processing of these grains was evaluated for its potential to modify ruminal fermentation and to improve milk production performance. A mixture of ground triticale and oats (CONG, at a ratio of 60:40 on a dry matter basis) was treated with urea (5 kg/1000 kg) and urease additive (20 kg/1000 kg) containing 200 g/kg of moisture, for 2 wk (UREG). The urea treatment enhanced the pH and CP content of grains by 34% and 52%, respectively. In a batch culture study, CONG or UREG as the only substrate was incubated in a buffered ruminal fluid. Compared to CONG, UREG increased pH, total VFA concentration, total gas, and disappearance of DM, while reducing CH₄ production, whereas NH₃ concentration increased and entodiniomorph counts tended to increase. In the in vivo study, cows were randomly allocated to two dietary groups (n = 24) and were offered TMR based on maize and grass silage, containing either 155 g/kg of CONG and 80 g/ kg of soybean meal (CONT) or 155 g/kg of UREG and 59 g/kg of soybean meal (URET) for 31 d. Ruminal fluid was collected (n = 10) using rumenocentesis. The relative abundances of Streptococcus bovis decreased, but Megasphaera elsdenii, methanogens, and ammonia-producing bacteria increased by URET. Entodiniomorph and holotrich counts were decreased by URET. Feeding with URET increased ruminal pH and concentrations of total VFA, acetate, branched-chain VFA, and NH₃. Feeding with URET also increased milk yield. These results demonstrate that replacing untreated triticale and oat grains with urea-treated grains can beneficially modulate ruminal microbiota and fermentation, consequently improving production performance and profitability.