Livestock fatten faster when tasked on Livestock Pens, Farms, and Villages.
—In-game description

Selective Breeding is a technology in Age of Empires III that can be researched by European civilizations at the Livestock Pen, while Native American civilizations and the Chinese can research it at the Farm and the Village respectively. Once researched, livestock such as Sheeps, Goats, Cows, Llamas and so forth, fattens 25% faster when they are tasked to Livestock Pens, Farms, and Villages.

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