Irrational pharmacotherapy with tetracyclines can cause mitochondrial cytopathies of liver cells and the development of toxic dystrophy. The issue of violation of the qualitative and quantitative composition of fatty acids and their functional role in the development of liver dystrophy has not been studied enough. Therefore, the aim of the work was to determine the features of changes in the fatty acid composition of blood serum and liver lipids in rats with tetracycline-induced hepatosis and the corrective efficacy of the phospholipid-acceptable dietary supplement “FLP-MD”. It was experimentally established that, in the composition of blood serum lipids and liver tissue, key changes in modeling tetracycline-induced hepatosis in rats (250 mg/kg for 7 days) are primarily tested for polyene fatty acids (PUFAs). In blood serum this is manifested by a decrease in the level of docosadiienoic (22:2ω6) and docosahexaenoic acid (22:6ω3), as well as the total PUFA content due to representatives of the ω3 family, respectively, by 1.3 times. At the same time, a decrease in the content of eicosapentenoic (20:5ω3), docosapentaenoic (22:5ω3), docosahexaenoic (22:6ω3) acids and the saturated/unsaturated fatty acid (SFA/UFA) and ω3/ω6 PUFA ratios, respectively, are noted in the lipid fraction of the liver, respectively by 1.3 times. In contrast to these animals, the use of reparative action of a phospholipid-acceptable dietary supplement “FLP-MD” (13.5 mg/kg) in sick rats provides a significant increase in the level of these fatty acids both in blood serum and in the liver and the restoration of their profile for other representatives. Thus, the components of the “FLP-MD” dietary supplement show a corrective effect on the fatty acid composition of the lipid component of blood serum and liver tissue of animals with tetracycline-induced hepatosis. Indicators have been experimentally established for the diagnosis of toxic liver damage and preclinical trials of the hepatoprotective efficacy of new drugs, which is a promising area of research in veterinary hepatopathology.