No effect was found (P > 0.05) of forage source or
supplementary HMBi on the excretion of N in feces,
urine, or milk and, therefore, diet had no effect (P >
0.05) on the efficiency of N use, calculated as N output
in milk divided by N intake in feed. The contribution
of PDI to milk production ranged from 1.06 kg/d to
1.09 kg/d and was not affected (P > 0.05) by dietary
treatment. The balance of PDI supplied by the diet
over that required for production and maintenance was
higher for animals offered CS-based diets (P = 0.02)
than for those offered GS-based diets.