Twelve cows (mean age 6·4 years) and eight sheep (mean age 0·8 years) were fed silage containing 70 to 90 per cent vitamin D3-effective Trisetum flavescens for a period of 14 weeks. At the beginning and the end of this period, the animals were examined and their kidneys, abdominal aortas and heart valves were examined by ultrasonography; the animals were then slaughtered and these organs were examined histologically, and the specificity and sensitivity of the ultrasonography were calculated. After the feeding period, all the cows had a decreased body temperature and all but one had raised hair, movement disorders and difficulty in rising and lying down. Ultrasonography of the abdominal aorta had a specificity of 90 per cent and a sensitivity of 75 per cent, and ultrasonography of the heart valves had a specificity of 100 per cent and a sensitivity of 50 per cent. In the sheep, cardiac arrythmia was the only pathological finding at the end of the feeding period, and the ultrasonographic examination of the kidneys had a specificity and sensitivity of 100 per cent.