Joseph didn't say animals are angels on earth. He said that those he saw in...
revelation were "like angels in their sphere". That sphere makes reference to a vision John saw in which there animals giving praise unto God in a celestial sphere. These were, in a sense, celestialized animals who had filled the measure of their creation. That doesn't mean all animals fit that description. And in fact, would suggest that animals in this realm are anything but that.
In order for them to be angels on earth, they would need to be able to speak by the power of the Holy Ghost. As you read through those quotes, yes, the prophets argue for humane, kind treatment of animals; however, in no way would any of them suggest they are on the same level as man, which is God's crowning creation. To use the scriptures and quotes of the prophets to suggest man should treat animals the same as man is wresting the scriptures.
Why is there so much of this on cougarboard lately. I feel like I'm in crazy town.