Preventing The Suffering Of Living Creatures

According to ethical tradition, prohibition against cruelty to animals is one of the basic laws of humankind.
The concern for the welfare of animals are accorded the same sensitivity as human beings. Indeed, animals are understood to not only have feelings but also have rights of existence and protection. They must be
treated as humanely as possible & be treated with mercy & compassion. It is required that animals be treated with consideration, kindness and respect just as one would their fellow human being.

Let's not fool ourselves about the impact of animal kindness on human beings' character. The primary principle behind the treatment of animals is preventing the suffering of living creatures. There is a fundamental connection between human beings and animals. Attitudes toward animals provide an excellent example.

There is a recognized link between the way a person treats animals and the way a person treats human beings. Such people may show similar aggression towards humans as well. A person who is cruel to a defenseless animal will undoubtedly be cruel to defenseless people & is likely to inflict pain & suffering on human beings. A person who cares for the lowest of creatures will certainly care for his fellow man.
We are not permitted to cause or inflict unnecessary pain to any living being. No distinction is made. This applies to bugs & creatures too. We must be very careful not to kill any bug, even the smallest and lowliest, such as fleas, lice, flies, and the like. 

Everything in creation has a special part in God's plan for unity. Everything has its place in the plan of creation and it is "good.". It becomes "very good" when all the parts are working in unison.
God  loves each of His creatures, and would not want pain inflicted upon them. Not even a moment's worth of pain if it can be avoided.