1. A composition containing an effective amount of lipoic acid or its salt for improving liver or immune function in an animal, wherein said amount of lipoic acid effective for improving liver or immune function in an animal is at least about 25 ppm. 2. The composition according to claim 1, where the effective amount is from 25 ppm up to 2600 ppm lipoic acid or its salt. 3. The composition according to claim 1, where the effective amount is from 50 ppm up to 1200 ppm lipoic acid or its salt. 4. The composition according to claim 1, where the effective amount is from 65 ppm up to 650 ppm lipoic acid or its salt. 5. The composition of claim 1, wherein the animal is a pet. The composition of claim 5, wherein the pet belongs to the feline family. The composition of claim 1, wherein the composition is a food composition. The composition of claim 7, wherein the food composition is a dry food composition. The composition of claim 7, wherein the food composition is extruded. The composition of claim 7, wherein the food composition is canned. A method for improving liver function or immune function in an animal in need thereof, comprising feeding an effective amount of lipoic acid or its salt to an animal, wherein said effective amount provides an improvement in liver function or immune system. The method according to claim 11, where the effective amount is from 25 ppm up to 2600 ppm lipoic acid or its salt. 13. The method according to claim 11, where the effective amount is from 50 ppm up to 1200 ppm lipoic acid or its salt. 14. The method according to claim 11, where the effective amount is from 65 ppm up to 650 ppm lipoic acid or its salt1. Композиция, содержащая эффективное количество липоевой кислоты или ее соли, для улучшения печеночной или иммунной функции у животного, где указанное эффективное для улучшения печеночной или иммунной функции у животного количество липоевой кислоты составляет, по меньшей мере, примерно 25 м.д.2. Композиция по п.1, где эффективное количес
