The animals chose the commandments because they wanted to keep the farm pure from human activity. They considered humans evil, and therefore tried to find ways to avoid emulating them.
Man is the only real enemy we have. Remove Man from the scene, and the root cause of hunger and overwork is abolished for ever. (ch 1)
Therefore the commandments were written to avoid man’s vices, or weaknesses and immoral deeds. There are commandments against killing other animals, but there are also rules against wearing clothes, sleeping in a bed, and drinking alcohol (ch 2). These are considered man’s weaknesses.
Although most humans consider killing a sin, you have to look a little deeper to find the problems with the other infractions. Wearing clothes could be considered vanity, and sleeping in a bed might be sloth (one of the deadly sins). Drinking alcohol is often considered gluttony.
The commandments do not last long. The pigs decide that they want some of these luxuries, and they begin changing the commandments.
the above link is to a Catholic site, or atleast has Catholic flavor to it- and explains some about how each Commandment (representative of virtue) on its opposite would be a vice. I hope this helps!!