God has made animals to serve humans for example goats and cows are slaughtered to provide meet,donkey and horse pull cart and weight.With endless efforts science introduces drugs for mankind.Before their practical application they are tried on animals.Experimentation on animal is the only way to check whether that drug suits human or not because in evolution lineage of vertebrates animals are very near to humans.Their system is almost identical to us.Direct application of new drugs on human may end up with loss of life.On the other hand animals also have pain receptors and yes a life exist in them ,but there is no alternate way except to use them.
