 There are well over half a million birds here, and every eight weeks or so, they're all replaced with half a million more. But none of her chicken poo will end up in the river. Once they go for slaughter, Jo scoops everything out of the huge barns, all the bedding and all the phosphorus-rich poo, and she shovels it into an incredibly high-tech incinerator, which she uses to heat the chicken sheds. But it's not just fuel for heating.