Effects of Supplemental Zinc in High Quality Diets on Ruminal Fermentation and Degradation of Urea In Vitro and In Vivo

© 2002 American Registry of Professional Animal Scientists Two experiments were conducted to investigate the effects of the addition of Zn to high quality diets on ruminal fermentation and hydrolysis of urea in vitro and in vivo. In Experiment 1, single effluent continuous culture fermentors were maintained on alfalfa hay-based diets with or without added Zn (400 ppm in total diet) for 4 d. On day 5, 2 g urea were added to the fermentors, and determination of concentrations of VFA and NH4+ in the fluid followed for 8 h. The addition of Zn did not affect concentrations of total VFA or NH4+ in the fluid from the fermentors. In Experiment 2, four non-lactating, Holstein cows previously fitted with ruminal cannulas were used in a switchback-designed experiment. Cows were fed the same diets used in the in vitro experiment at restricted (5.71 kg DM) intakes. The addition of Zn to these diets had no impact on ruminal NH4+ concentrations or concentrations of total VFA in ruminal fluid. However, the addition of Zn to diets did change proportions of individual VFA in ruminal fluid. The proportion of propi-onate tended to increase, and the proportion of butyrate tended to decrease, when Zn was added to the diets. These data indicate that supplemental Zn was ineffective in preventing urea hydrolysis when fed with high quality diets but was effective in altering the fermentation pattern