EN
Effect of both vitamin D₃ and cadmium (Cd) on chymotrypsin activity (ACHT) of laying hen has been studied. Ten month-old laying hens were fed a compound feed of HYD-10 ad libitum. The birds were divided into 8 groups (each group consisting of 6 birds) as follows: experimental groups G1, G3, and G5 were supplemented with Cd (0.3; 0.6; and 6.0 mg.kg⁻¹ CdCl₂, respectively) groups G2, G4, and G6 were supplemented with vitamin D₃ (100 I.U./day) at the same Cd concentrations. C₁ was control group without any supplements and C₂ was control group supplemented only with vitamin D₃. The study lasted 6 months. In groups G1-G4, ACHT activities in the end of the study were rather high (2097.4; 2984; 1805.4, and 2575.9 U.g⁻¹,respectively). The ACHT activity in groups G2, G4 and G6 was by little higher than that in groups G1, G3, and G5 without vitamin D₃ supplementation. The principle of the action of vitamin D₃ via Ca ions and calmodulin is further discussed.