Fat is an important component of feed rations for poultry as it improves the growth and laying parameters, which translates into better economic outcomes of animal production. The quality of this nutrient is determined by its freshness. It was assumed that the addition of oxidised fat with a peroxide value below 6 mEq O₂/kg in the ration does not trigger any clinical symptoms or morphologic changes in the internal organs in poultry. Fat with a higher degree of oxidation is harmful to animal health and thus reduces the performance. The products of hydrolysis and oxidation of higher fatty acids demonstrate cytotoxic effects and lead to metabolic disturbances. As a result, this results in morphological changes with both a destructive and adaptive nature. These changes are mainly observed in the gastrointestinal tract, liver, kidneys, skin, skeletal muscles and heart in different avian species. Furthermore, poultry becomes more susceptible to viral and bacterial infections. Disease cases resulting from feeding oxidised fats to poultry often become a hot spot and a source of conflict between a feed provided and a customer. They also require veterinary attendance and interventions. In such a circumstances, the first stage of treatment always consists in a change in the current feed for a novel, good quality feed mix. In addition, detoxifying, hepatoprotective and protective medications are warranted.