Milk urea nitrogen was linearly increased (P < 0.05)
as the level of dried molasses increased (Table 2). The
higher NPN content for the molasses-supplemented
diets relative to the control diet (Table 1) may explain
the differences observed in MUN in the current study.
Factors influencing MUN include CP intake, percentage
of ruminal degradable and undegradable protein, and
dietary protein:energy ratio (Nousiainen et al., 2004).
Our results suggest that inclusion of dried molasses
in dairy cow diets may have adverse effects on animal
performance, as indicated by increased MUN concentration.
In accordance with our findings, Broderick et
al. (2002) reported that feeding a source of RUP, such
as extruded soybean meal, improved milk production of
lactating cows fed a high-alfalfa silage diet with NPN
supplying 56% of dietary CP. Results of the current
study demonstrate clear differences in microbial growth
and fermentation rates between dry molasses and corn
starch.
In the current study, dried molasses replaced highmoisture
corn as the energy source. It has been suggested
that molasses contain less energy due to its high
ash content (i.e., 15% of the DM) and lack of hexose
polymers. This may explain some of the adverse effects