First, the tigers in Guangzhou Zoo are South China tigers, which are generally small in size and are the offspring of inbreeding.
As we all know, the South China tiger is basically extinct. At present, there are no wild South China tigers in China. These South China tigers in Guangzhou Zoo are all descendants of six wild South China tigers. From the original six to more than 200 now, these are basically close relatives, so there will be some genetic defects, such as small size, poor digestion and absorption ability and so on. The South China tiger itself is lean, not as big as the Northeast dialect and Bengal tiger. South China tiger has no fat and looks smaller. This has a lot to do with the environment, just as southerners are generally petite than northerners.
Second, tigers in the zoo have little room to move, and they don't hunt in the wild, so they are not suitable for being too fat.
In fact, the animals in the zoo are similar to our own private pets, and they are all kept in captivity. Their activity space is very small, and their daily demand for energy is not so high. Moreover, human pets can go out for a walk regularly every day, but the range of animals in the zoo is very small, so they may not be able to digest if they eat too much.
Some people say that they saw tigers eating bark because they were hungry, so they thought it was the zoo that abused animals. In fact, it doesn't matter whether the tiger eats trees or not, but it just courts.