What to Do When Your Horse Has Cattle Grubs?

A cattle grub is the larvae stage of the adult heel fly, so named because the females hover in the rear loin and heel areas of bovines, depositing eggs on the hair. Though these pests typically target cattle, they have also been found infesting equines, bison, sheep and goats that pasture with or near infected cattle.

  1. Life Cycle

    • The adult bee-like heel flies are usually found from February through May, but can appear at other times based on location. Adults infest horses by attaching eggs to individual strands of hair at the beginning of fly season. The eggs hatch within three to seven days and cattle grubs creep down the hair, perforate the skin, and commence their migratory excursion through the connective tissue within the horse's body. The cattle grub lies dormant within the body after two to four months, then enter a rapid-growth stage under the skin on the horse's back.

    Dangers

    • Cattle grubs feasting on horses are unable to mature completely, whereas those with cattle hosts emerge through the skin, descend to the ground and pupate. After migrating to a horse's head, neck, withers and rib areas, cattle grubs remain beneath the skin and form hard nodules. These tubercles may turn into sores, especially if a saddle rubs the affected area.

    Treatment

    • Cattle grubs generally do not cause problems for horses, other than possible discomfort under saddle. The most successful way to control cattle grubs in horses is to control them in nearby cattle. Other means of treatment include lancing the swollen area to physically remove the cattle grubs or applying injectable or spray-on insecticides soon after fly season ends.

    Prevention

    • Successful cattle grub control involves community-wide management. Treating nearby cattle prior to the fall cut-off period, when the cattle grubs are around the esophagus or spinal cord, is the most aggressive method. Treatment outside of this time frame may risk choking or paralysis of the host animals. Removing the dangers within surrounding cattle herds drastically reduces the risk of equine infestation.