SummaryGlucose and insulin concentrations of jugular blood plasma were monitored in growing lambs over 8 h, following a 2 h infusion of acetate, propionate,n‐butyrate,n‐valerate and physiological saline into the ruminal vein. Propionate and especiallyn‐valerate infusion significantly increased blood glucose concentration.n‐Butyrate induced only a small increase of shorter duration, while acetate failed to exert a pronounced effect on the blood glucose level. SCFA infusion, except for acetate, raised the insulin level in the blood. Relative rise was closely correlated with the length of carbon chain of the SCFA, that is,n‐valerate caused the largest elevation of the insulin level, followed byn‐butyrate and propionate. At the same time, acetate failed to cause a marked influence on the insulin level. These results of insulin showed agreement with glucose concentration changes, with the exception ofn‐butyrate treatment, where the increase of plasma insulin concentrations after the infusion proved to be much larger than that of glucose, relative to the prei