INVESTIGATIONS ON THE EFFECT OF VARIOUS R IBOFLAVIN SUPPLEMENTATIONS DURING LACTATION ON RIBOFLAVIN CONCENTRATIONS OF MILK, LIVER AND CARCASS IN LACTATING RATS

The present study investigated the effect of various dietary riboflavi n supplementations (0 to 4 000 mg/kg) during lactation on riboflavin c oncentrations of liver, carcass (bled body without intestine and liver ), and milk in the rat. The experiment was conducted until the 14(th) day of lactation; milk samples were drawn on the 7(th) and 13(th) day of lactation. Riboflavin concentrations of milk raised continuously wi th increasing riboflavin supplementation; in the range between 0 and 1 0 mg/kg riboflavin supplementation, there was a linear relationship, a nd in the range between 12 and 4 000 mg/kg there was a logarithmic rel ationship between riboflavin supplementation and riboflavin concentrat ion in the milk. Maximum riboflavin concentration of milk obtained by supplementation with 4 000 mg/kg was twelve-fold higher than without r iboflavin supplementation. For riboflavin supplementation up to 12 mg/ kg, riboflavin concentrations in milk on the 7(th) day of lactation an d that on the 13(th) day of lactation were not different. In contrast, in rats fed diets with higher riboflavin supplementation, riboflavin concentrations were higher by 25 % in average in milk on the 13(th) da y of lactation than in milk on the 7(th) day of lactation. Contrary to the milk, riboflavin concentrations in liver and carcass exhibited a saturation, which was achieved at a supplementation of 6 mg/kg (liver) and 10 mg/kg (carcass), respectively. Maximum riboflavin concentratio ns obtained at a supplementation of 4 000 mg/kg were 1.9- and 2.3-fold higher for liver and carcass, respectively, than concentrations obtai ned without riboflavin supplementation. The dose-response relationship using riboflavin concentrations of liver and carcass as response fact ors indicates a riboflavin requirement of 8 to 9 mg/kg for lactating r ats fed a semisynthetic diet with 17.4 MJ ME/kg dry matter and 20.8 % protein in dry matter.