Neither forage source nor supplementary HMBi
altered N output in the current study. Replacing GS
with CS in the forage DM resulted in increased DMI
and N intake. However, no subsequent improvements
in milk N output occurred and, consequently, urinary
urea excretion was higher with CS-based diets. Animals
did not appear to be limited by the supply of available
methionine at the production levels reported herein.
Therefore, improvements in milk yield and milk N output
were not observed where diets containing 13.5% CP
were supplemented with HMBi. Improvements in the
DMD, UFL, and CP content of GS offered and the use
of higher-yielding cows may alter these results, highlighting
an area where further investigation is required.