A horse rug according to the present disclosure provides one or more flex control extender inserts for animal accessories permitting the accessory to flex with the animal while conforming to the animal. In a horse rug or blanket, stable blanket, turnout cover or other named horse cover, the flex control extenders may be used along the neck opening at the withers and or at the shoulders or any suitable combination. A horse rug according to the present disclosure may be suitable for use in rugs or blankets with or without neck hoods.