Lice! 🦟 Lice infestation in horses can be a significant problem and is more frequently encountered in the winter. This is because lice hide in the horses long winter hair coat. Lice also tend to show up more on horses that are "stressed" by a large herd population, inadequate nutrition, severe cold weather, illness or injury. Horses with lice tend to look rough or unthrifty with a scruffy hair coat as they continually rub and scratch. Lice are easily passed from horse to horse by direct contact