Effects of sun-curing, formic acid-treatment or microbial inoculation of timothy on urea metabolism in lactating dairy cows

Abstract

Urea metabolism was estimated in dairy cows fed forage conserved as hay, formic acid-treated silage or microbial inoculated silage. Use of [ 15N15N]urea kinetics indicated that urea-N 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.