[en] A living body component analysis of domestic animals by a prompt gamma-ray analysis (PGA) was developed. By this method, dynamic behavior of trace element in the living body was studied. Moreover, movement of diets in the digestive tube was analyzed by use of new activable tracers (Sm, La and Yb, etc.). Feed alfalfa hay cube (1100 g/day/sheep) and water with boron (100 ppm boron) to three sheep for 18 days. The concentration of boron in the plasma, urine and feces increased rapidly after feeding water with boron and reached the standard level after 3 to 5 days. Boron in drinking water was absorbed rapidly and discharged from urine. The concentration of boron in the organ was 10 times as much as control one and boron was storage in the liver. On movement of feed in the digestive tube, a determination method of element was established by feeding goat, calf and milk cow to diet labeled with Sm, La and Yb and amount of element in feces was analyzed by a thermal neutron activation analysis. (S.Y.)