DUODENAL INFUSION OF OIL IN MIDLACTATION COWS .7. INTERACTION WITH NIACIN ON RESPONSES TO GLUCOSE, INSULIN, AND BETA-AGONIST CHALLENGES

Metabolic effects of rapeseed oil, niacin, or both were investigated f or multiparous Holstein-Friesian cows in midlactation. Cows were conti nuously infused with water (control), rapeseed oil, niacin, or rapesee d oil plus niacin into the proximal duodenum, using a 4 x 4 Latin squa re design. Oil infusion resulted in higher plasma concentrations of ch olesterol and urea, but a lower plasma concentration of glucose, witho ut changing basal concentrations of insulin, NEFA, and BHBA in plasma or causing a difference in the concentration of metabolites in jugular versus mammary vein plasma. Effects of niacin were small and nonsigni ficant for almost all of these measurements. Responses of plasma gluco se, NEFA, and insulin to challenges by isoproterenol (beta-agonist), g lucose, or insulin were studied. Rapeseed oil infusion lowered glucose tolerance. Niacin infusion increased responses by glucose and insulin to glucose challenge. Oil and niacin negatively interacted for respon ses of plasma concentrations of glucose and insulin to isoproterenol c hallenge. Positive energy balance in midlactation cows possibly masked potential niacin effects on the studied measurements.