I am not sure that cows or chickens use many liver flushes or liver tonics.
I agree that a healthy liver is key to good health. You simply cannot have good health without a healthy liver. Conversely, if you are unhealthy, your liver is probably unhelathy too.
On the other hand, one should also not justify health sins with the idea that a liver tonic will repair any damage that comes along. A liver tonic is a good idea if you have a damaged and impaired liver; however, one should also maintain a healthy liver by practicing good health on a regular basis.
The liver is designed to repair and rebuild itself and a liver tonic can help a lot. However, it will not repair all the damage to the rest of the body that bad diet and lifestyle will cause.