The nerve damage is commonly caused by horses colliding with other horses or objects.....ie stall doors, trees...etc. Nerve damage is also caused by ill fitting work collars putting pressure on the nerve. This is seen in horses which are used to pull wagons, carts and freight.
Pain may or may not be present in the affected limb. As the muscles atrophy worsens, the horse may have difficulty extending the forelimb. Also, horses may swing their shoulder out due to instability or loosening of the shoulder joint from lack of muscle and ligament tone.
Treatment of sweeney involves anti-inflammatories and physical therapy. Nerves can heal and possibly even regenerate if the injury is not too extensive and enough time is allowed. Muscle massage and electrical stimulation has been used. For cases with extensive scarring, surgery can be performed to release the nerve and hopefully regain function. In the case of a poorly fitted collar, rest and a properly adjusted collar is indicated.