From tongue rolling alpacas to irritable yaks and perturbed pigs, new research has lifted the lid on why some farm and zoo animals cope well with captivity and others display signs of stress. Researchers have published a large-scale study to identify which species of hoofed animals, known as ungulates, are better suited to captive environments and which require better husbandry if kept in captivity.From tongue rolling alpacas to irritable yaks and perturbed pigs, new research has lifted the lid on why some farm and zoo animals cope well with captivity and others display signs of stress. Researchers have published a large-scale study to identify which species of hoofed animals, known as ungulates, are better suited to captive environments and which require better husbandry if kept in captivity.