How are the animals characterized?

All of the animals are given human characteristics, but none are fully fleshed out into three-dimensional figures.
First, certain types of animals are grouped together and given only one or two major characteristics. The sheep, for example, are very unintelligent and easily brainwashed and led by the pigs. The hens, on the other hand, have more intelligence and are fiercely protective of their eggs (their unborn children), even standing up to Napoleon to try to protect them, although to no avail. The dogs are fierce and loyal to the pigs.
A few of the animals do get individualized. Mollie, for instance, is a horse who loves to wear ribbons and eat sugar: she is silly and would rather have her material comforts than be free. Moses is a sly liar of a raven who will weave false tales about Sugarcandy Mountain in return for food so that he doesn't have to do any real work. Squealer is a slimy, smooth-talking pig with a curly tail who is always jumping from side to side. He would creep out anyone with half a brain, but most of the animals lack that level of intelligence. Snowball is a very intelligent and dedicated pig who nevertheless is willing to grab privileges for his own kind, such as all the windfall apples. Napoleon is a power-hungry, ruthless, and shrewd pig who is not particularly bright.
A hero of the book is Boxer, the workhorse who truly believes in the rebellion and, later, in Napoleon. He represents the person of sincere heart who always goes the extra mile, only to be betrayed and cheated for his efforts. However, even Boxer is not very developed: we know him only as a caring and trusting horse who always works hard.

In George Orwell’s Animal Farm, the animals are portrayed as having human characteristics. The novel is an allegory about the causes and effects of the Russian Revolution, and the animals each represent different segments of Soviet society. In the beginning, all of the animals are subjected to the tyranny of their master, Farmer Jones, and the differences between the species are minimized. However, once the animals gain their freedom, their differences become more apparent and determine their place on the farm. For example, after an idyllic period in which the commandment is adopted that “all animals are equal,” the pigs quickly use their superior intelligence to rule over the other animals. The horses, Boxer and Clover, are the exploited working class and accept the pigs’ rule unquestioningly, while the dogs protect the pigs and use force and intimidation to quell any dissension. The hens try to rebel against the tyrannical rule of the pigs but are starved out, and their rebellion is quashed. Idealism gives way to “human nature,” and the animals trade one form of tyranny for another.