Four Holstein steers (mean
body weight, 211 +/- 20 kg) were utilized in a Latin-square design with a 2 X 2 factorial arrangement of treatments to investigate the effects of
monensin (0 or 220 mg/d) and
sodium propionate (0 or 450 g/d) on net nutrient flux. Steers were surgically prepared with hepatic portal and mesenteric venous
catheters and an elevated carotid artery, after which they were adjusted to their basal diet (85% concentrate) and initial treatment over 19 d. Samples of arterial and portal venous blood were taken hourly over 3 h for the final 3 d of each 2-wk period. Portal blood flow was determined by primed continuous infusion of para-aminohippurate. No changes were seen in dry matter intake, portal blood flow, or net portal flux of any of the
volatile fatty acids with the exception of
butyrate flux, which decreased with
monensin addition. Addition of
monensin decreased net portal flux of
ammonia, decreased recycling of
urea, and tended to increase the net portal flux of
glucose. Addition of
sodium propionate increased the net portal flux of
glucose and decreased the net portal flux of alpha-amino-N. These results are interpreted to suggest that changes in the products of ruminal fermentation may not be exactly translated into the products appearing in the portal circulation, and more information is needed to describe these relationships.