The chemical processes occurring in the animal body under pathological conditions are of interest to researchers. The objective of the research was to study the indicators of lipid peroxidation and antioxidant activity in horses infested with helminthiases and treated with anthelmintic paste with an antioxidant. The study has proved the role of parasitic infestation in accelerating the processes of free radical oxidation, which is manifested by a decrease in the light sum of radicals (36.62-39.21), the maximum luminous intensity (6.13-6.98) and antioxidant activity (5.65-6.2) at the start of the research. Chronic invasion increases the concentration of under-oxidized products up to 38.59, and the rate of initiating free radical oxidation – up to 6.95, the values of antioxidant activity being stably low (5.51-5.91). An important role in the regulation of lipid peroxidation in horses during helminthiases, as well as in the process of deworming, is played by the antioxidants contained in anthelmintic preparations. The antioxidant santohin included as a compound in the «Alezan» preparation suppresses enhanced peroxidation and activates the antioxidant protection of the body, which is reflected in a decrease in the light sum of the radicals to as low as 26.73, a maximum luminous intensity to – 3.76, and an increase in antioxidant activity – up to 7.16.

Parasitic invasions in horses often cause metabolic disorders and have a negative impact on their health and performance. The purpose of this research was to study the processes of lipid peroxidation and antioxidant protection in horse helminthiases, as well as following the deworming with a drug containing the antioxidant santoquine. The intensity of lipid peroxidation and antioxidant protection was determined in horses with different degrees of invasion by concentrations of malondialdehyde and ceruloplasmin accumulated in the blood. The studies have revealed that the concentration of malondialdehyde, the end product of free radical oxidation of cell membrane phospholipids, depends on the intensity of infestation with intestinal nematodes. In horses infested with paraskaris and intestinal strongylata, a significant accumulation of malondialdehyde was by 18.2% higher as compared to uninfected animals. The level of ceruloplasmin was significantly lower – by 21.8% in animals with a moderate degree of invasion as compared to clinically healthy animals. To neutralize free radicals the antioxidant santoquine was used. Effective deworming by means of using santoquine reduced the intensity of lipid peroxidation processes, which resulted in a significant decrease in the concentration of malondialdehyde by 22.1% and an increase in the level of ceruloplasmin against the background of the lower rate of free radical oxidation by 25.8%.