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The video is very hard to watch.

Pregnant pigs, crammed into crates with open wounds.

Mercy for Animalsreleased undercover video at Minnesota's Christensen Farms showing horrific abuse.

"Gestation crates deprive animals of even the most basic natural behaviors and needs and as a result, these animals go insane," Mercy for Animals spokesperson Nathan Runkle said.

This week, Costco and K-Mart joinedseveral grocery chains in requiring pork suppliers to stop using gestation crates.

In a statement, Walmartsaid it offers gestation crate-free pork products at several stores adding:

"We will continueon-going discussions with our suppliers, non-governmental organizations and food safety experts to find ways to increase that number," Walmart spokesperson Deisha Galberth said.

Nine states including California have banned the use of gestation crates.