Rectal palpation can be revealing, but the procedure is not without risk. Karen Coumbe MRCVS offers some inside information
Every routine procedure is potentially hazardous. The classic example is rectal palpation, which has to be one of every equine vet’s worst nightmares when complications arise.
This common diagnostic technique is used routinely by many vets on almost a daily basis. Palpation of the internal abdominal organs through the horse’s rectum is an essential part of many clinical examinations and, in the vast majority of cases, a relatively low-risk procedure.
Almost every time a vet examines a horse with colic, or a breeding mare, an internal or rectal examination is required. Few vets feel it necessary to warn the horse owner that there is even a remote chance that something may go wrong. It is a difficult balance between worrying people and informed consent as to what might just happen.
The reality, however, is that – very occasionally – either horse or vet will suffer an injury.
Young animals are at greater risk of sustaining a rectal tear injury, owing to their smaller size and frequent reluctance to remain stationary. Similarly, donkeys, small ponies and Arabian horses may have an increased risk due to their size and temperament, which is not always best suited to standing still for the procedure.
While broodmares that undergo the procedure regularly usually tolerate it well, stallions are typically less frequently examined and may prove more challenging. Certainly, nervous horses and those unaccustomed to rectal palpation can be more problematic.
The chance of injury to horse or human is always reduced with good facilities, such as stocks, and knowledgeable handlers, as found at reputable studs.
The rectum is essentially a storage chamber for droppings, measuring about 30cm in length and therefore stretching from the average vet’s hand to beyond his or her elbow.
Anatomically, it is divided into two sections: a peritoneal section, which is further forwards, closer to the abdominal organs, and a section at the rear that is described as retroperitoneal and is possibly more robust.
The main blood supply runs along the top of the rectum, which is where the more severe tears are likely to happen. The section furthest forward is particularly vulnerable, where there is a “pull” from the rest of the intestines as the rectum contracts.
Studies show that damage tends to happen because the horse tightens the rectum around the vet’s hand, tearing the lining or further layers of tissue.
A rectal tear most commonly occurs during palpation of the caudal (rear) abdominal reproductive organs as part of a fertility examination. The vet may use a diagnostic ultrasound probe to check the mare’s uterus and ovaries, so care must be taken as there is only so much room within the rectum. This small, blunt-ended instrument is designed to fit between the vet’s fingers, so it is unlikely to cause trauma.
The next most common occurrence is during a colic examination. Vet students are taught that rectal palpation is an essential part of a colic investigation, unless there is an extremely good reason not to do so. It is unusual that a definitive diagnosis can be obtained in any other way, such as by using external abdominal ultrasound.
Not all tears occur as a result of veterinary examination. Rarely, a spontaneous rectal rupture can occur – especially if there is some form of bowel weakness. This may be caused by issues, such as excessive retention of droppings, that are possibly associated with melanomas around the horse’s rear or another blockage, such as an abscess. Unexplained rectal tears have been recorded in elderly ponies with Cushing’s disease.
Breeding injuries, either at covering or foaling, can also cause rectal damage. Equally, a foal may be injured when an enema is administered, so this must always be done with extreme care.
Red for danger
Every vet dreads the sight of fresh blood on their rectal sleeve, alerting them that damage has occurred. A more detailed examination is then required to find out the severity of any injury.
Acknowledging and communicating that the horse has potentially sustained a serious internal injury is one of the most difficult parts of any vet’s job. It is important that both owner and handlers are made aware of potential problems; if a horse has sustained a minor rectal injury on one examination, extreme caution must be exercised the next time the procedure is performed.
It is vital to act immediately, giving appropriate first aid to improve the patient’s chances of survival. Without dwelling on the grisly details, a full-thickness tear in the bowel wall will allow the gut contents to leak out. Sadly, this is likely to result in fatal peritonitis or internal infection.
Vets use a grading system for rectal tears, with the worst being grade four where abdominal contamination occurs. In a report of more than 40 horses with the more severe (grade three or four) tears, more than half did not survive. With intensive treatment including surgery, however, some do make a full recovery.
The prognosis for a more minor grade one tear is excellent. With a laxative diet and appropriate medical treatment, the horse should fully recover.
Survival depends largely on the severity of the tear and the course of action taken at the time of injury. A rectal tear is not something that can be ignored – it’s never a case of just “wait and see”. It is vital to establish how serious the internal damage is and prevent further complications.
The most serious tears are acute emergencies. The horse should be given an epidural and/or other treatment, to reduce any rectal straining, as well as sedation, and will require referral to an equine hospital.
In summary, rectal examination does carry risks. If your vet thinks your horse needs sedation, or anything else to facilitate the procedure such as medication to relax the hind gut, always agree.
Your vet may prefer to work around a stable doorway that can act as a barrier or request that one of the horse’s legs is lifted. The ideal scenario is with the horse secured in a set of stocks, but if this is not possible, above all try to avoid carrying out the procedure when he is in the middle of a field with minimal restraint.
Rectal tears have been documented as having occurred regardless of the expertise of the vets and handlers involved. However, while the risks and benefits of rectal palpation need to be balanced to do the best for every horse, it is worth remembering that large numbers of examinations are performed safely, that the chance of injury is small and that even if damage does occur, it may be mendable.
Veterinary students are taught how to perform a rectal examination by working very carefully with the natural contractions of the horse’s bowel and never to rush the procedure.
It takes practice to be able to insert a lubricated, gloved arm into a horse’s rectum to identify the various internal structures through the rectal wall. Students must then learn to recognise anything that appears abnormal or out of place, feeling for blockages or a build-up of gas or fluid, as well as palpating other organs, such as the bladder, uterus, ovaries and spleen – using their fingertips as “eyes”.
Much of the initial training takes place using a dummy of a horse abdomen, creating a near-realistic set-up that allows students to perfect their technique. In studies at the University of Veterinary Medicine in Vienna, Austria, simulator-based training was found to be very effective for preparing students to perform diagnostic procedures on live horses.
Ref Horse & Hound; 9 April 2020