Bull calves, white and black breed, were investigated. During the autumn and winter season, the animals investigated were fed mixed feed. The feed types applied were enriched by some feed supplements, such as: beef tallow, calcium soaps made of tallow, colza soaps made on the basis o f colza oil, and amides of fatty acids. It was stated that natural and chemically modified animal fats (tallow) and colza oil, if added to the feed for bull calves, increase their growth increase and improves their carcasses. When tallow and its derivates were applied, the production outcome, expressed by a dressed yield index, was higher.