We do strange things in the interest of being humane. This article talks about research into non-surgical animal sterilization in the interest of preventing population explosions in animals like dogs, cats, and (to my surprise) horses. An individual has contributed $75 million to the cause.
I can sympathize with the desire to reduce the amount of suffering in the world, in non-human animals included. But when there are people like Aubrey de Grey out there who have viable plans to dramatically reduce human suffering and who are struggling to find funding for their research, I question the importance of things like animal contraception.
Its also a bit interesting from the standpoint of the gene: we're certainly doing the species' no favors by sterilizing large numbers of their members. But of course, we sympathize with and anthropomorphize the individual cute cuddly animals, not the abstractions that are their genes.