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Foals with an overbite, commonly called a parrot mouth, have upper incisors that protrude past the lower incisors. While some breeders droop their shoulders and shake their heads when faced with affected foals, floundering in their misfortune, others pick up the phone and call the equine orthodontist.

Parrot mouth, long believed to be an inherited condition, reportedly affects 2-5% of the equine population to some degree. Although common in other species, like humans, any degree of overbite is considered abnormal in horses.

“Other animals with an overshot jaw have difficulty grasping food because of misaligned incisors. In horses, incisor malalignment is obvious but not necessarily a significant problem, because they are capable of seizing food with their lips. The major concern is the potential development of cheek-teeth disorders that inhibit their ability to chew,” shared Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research.

Foals with an overshot jaw are therefore at risk of malnutrition, slow growth, and the development of additional dental problems. For example, lack of contact between the upper and lower incisors can result in overgrowth of incisors and cheek teeth, known as premolars. In addition, this lack of contact may trap the lower incisors behind the upper incisors, potentially contributing to the lack of lower jaw growth, which exacerbates the condition as the foal grows.

According to a recent study*, tension band wires on the upper dental arcade either with or without the use of a bite plate on the floor of the mouth, under the tongue, successfully corrects or improves the condition. Researchers reported the following observations from the study:

  • A reduction in overbite was achieved in >90% of treated foals;
  • Complete reduction occurred in 25% of foals, whereas a function reduction was noted in 51%;
  • Foals required one to four dental implants; and
  • Younger foals were more amenable to treatment, with faster and more complete correction.

“Despite these positive results, owners should be aware that treated foals require skull radiographs, at least two surgical procedures performed under general anesthesia, and may have post-treatment complications,” warned Crandell.

Such complications include facial-nerve injuries, irritation to the mare’s udder during nursing, and discoloration and abnormal growth of the incisors.

In addition, it may not be ethical to breed animals with corrected bites, considering parrot mouth is strongly believed to be an inherited unsoundness.

*Easley, J., P.M. Dixon, and R.J. Reardon. Orthodontic correction of overjet/overbite (“parrot mouth”) in 73 foals (1999 – 2013). Equine Veterinary Journal. In press.

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