Urea metabolism was estimated in dairy cows fed forage conserved as hay, formic acidtreated silage or microbial inoculated silage. Use of [¹⁵N¹⁵N]urea kinetics indicated that ureaN production was greatest (P<0.05) with inoculated silage. Gut entry rate of urea-N was not affected by treatments. Urea-N recycled to ornithine cycle tended to be greater (P<0.08) when cows received inoculated silage compared to when fed acid-treated silage. The proportion of recycled urea-N lost in faeces was greater (P<0.05) when cows were fed forage conserved as hay as opposed to when fed inoculated silage. Overall, urea metabolism was similar between cows fed formic acid-treated silage or hay. Inoculated silage, however, increases urea production and recycling to the ornithine cycle.