In an experiment carried out on 3 groups of fatteners, the effect of a high proportion of naked oat (55%) and the addition of synthetic zeolite (3%) on production results was studied. The control group received a mixture with 55% barley. The fatteners receiving the oat without added zeolite had the highest body weight gains (855 g) and the best feed efficiency (2.81 kg per 1 kg), but the differences were not statistically significant. The addition of zeolite caused a significant increase of digestibility coefficients of all nutrients. Zeolite also improved the indices of nitrogen balance, expressed by significantly smaller excretion of nitrogen with faeces and higher nitrogen retention in fatteners at 70 kg body weight.