How strong is a wild hog's sense of smell?

Wild Hogs, Feral Pigs and Russian Boars and Wild Pigs

The wild pig’s sense of smell is well developed and is much better than both their eyesight and hearing - they rely strongly on their sense of smell to detect danger and search out food. They are capable of sensing some odors up to seven (7) miles away and may be able to detect odors as much as 25 feet underground! Appealing to this tremendous sense of smell - fermented or scented baits can provide additional attraction to make them more vulnerable to trapping and shooting.