3. Results and discussion
3.1. Effect on BW change, feed intake, nutrient intake
and digestibility
Effect of CP levels in TMR on BW change, voluntary
feed intake, nutrient intake and nutrient digestibility in
lactating dairy cows are presented in Table 2. The BW
change range of all treatments was 0.2–0.4 kg/d during
the experimental period and was not significantly altered
by dietary CP content. Daily total DM intake ranged
from 10.2 to 14.3 kg/d and dairy CP and organic matter
(OM) intake significantly increased with increasing
dietary CP level (P < 0.05). In general, it is well known
that feed intake increases as dietary CP level increases
(Argüello et al. 2003; Broderick & Reynal 2009;
Hwangbo et al. 2009). Similarly, in this study showed
that there was significant difference in daily total DM
intake among treatments. The result from present study
was similar to those from Broderick (2003) who reported
that feed intake of DM was lower on 15.1% CP than at
16.7% and 18.4% CP and earlier studies reported that
daily CP intake increased as CP level in feed increased
(Hwangbo et al. 2009).
Digestion coefficient of nutrients did not significantly
differed between diets (P > 0.05). In agreement
with these observations, Hristov et al. (2004) reported
that ruminal apparent or true digestibility of DM, OM,
NDF and N was not affected by 15.8% or 18.3% of CP
in the diets. However, under the current experiment,
digestibilities were lower than those reported by Wanapat
et al. (2009a).