Overall, concentrations of urea in the plasma and
milk reported herein were lower than those reported
in Olmos Colmenero and Broderick (2006), despite CP
levels being similar (133 vs. 135 g/kg of DM). The diurnal
pattern of urea concentration in plasma (Gustafsson
and Palmquist, 1993) and differences in milk urea
analysis (infrared vs. colorimetric; Broderick, 2003)
may partially account for the disparity between these
studies. However no indication exists that the animals
used in this experiment were restricted by dietary CP,
as MUN was above the 1.4 mmol/L lower threshold
suggested by Vérité et al. (1996). The increase in urinary
allantoin excretion from animals offered GS-based
diets suggests a greater flow of microbial N to the small
intestine with these diets (Broderick, 2003).