Technological advances in last decades of XX centuries were well utilised in the studies of biological oxidation processes. Biological oxidation can lead to the oxidative stress and subsequently to the cell damage of animal organisms leading to many diseases. Free radical processes taking place in cattle under pathological conditions. Metal ions are often responsible for the damage of biological systems. Fenton and the Fenton like reactions can play the central role in the oxidative stress. Transition metal ions and their complexes catalyse Fenton and the Fenton like reactions.