A pig is designed to root in the soil, Friedrich said. A chicken is designed to build a nest. So keeping those animals -- and others raised as commodities -- in cramped cages, away from sunlight, dirt, grass and, often, companionship, is a "denial of God's will," Friedrich argues.
He and others also point out that God set forth a vegetarian diet for man in the creation story in the Book of Genesis. Only after sin, fall and the expulsion from Eden does the Bible speak of man eating animal flesh.
The Bible is, of course, replete with examples of God ordering animal sacrifice. But animal-rights activists contend that God's true ideal is compassion and dignity for all creation.
The religious argument can be so persuasive that even the nonreligious have learned to use it on behalf of animal rights.
Bernard E. Rollin, a noted animal ethicist, is not a person of faith. Still, he quotes the Bible when he talks to meat producers, trying to convince them that modern industrial methods trample on God's ideals about respecting animals.
That argument resonates widely, said Rollin, a professor at Colorado State University. So he expects to hear a lot more talk about faith from animal-rights activists in years to come.
"A lot of this country is religious, and all those religious people eat food," Rollin said. "Whatever works."