Suicide Barnyard: a digression

According to a letter published in the November 30 New Yorker and written by a Mr. G. of Salt Lake City, Utah, it could hardly be more plain that animals want to be killed on small, family farms:

Is it better for aging animals to suffer, blind, arthritic, starving, or cancerous until merciful death? I grew up on a farm and can say with certainty that our animals gave their bodies in gratitude for a well-cared-for life. (Emphasis added.)

Not only do the animals participate consciously in some sort of exchange of services, à la Derrick Jensen's "bargain", but it is as if the entire process—their breeding, raising, and slaughter—were something the animals themselves established!

Can the humans be blamed simply for following the orders of their livestock masters?