Primary conditions

Primary kidney problems are extremely rare in the adult horse, and are normally caused by an ascending infection resulting from cystitis. Both kidneys will be affected. The normal isolate is Corynebacterium spp. The main signs are general malaise and pyrexia; diagnosis is aided by rectal ultrasound or manual palpation. The kidneys are usually found to be painful. Urea and creatinine levels will be raised; culture of the urine is not helpful as the infection may come from lower down the urinary tract. Haematogenous infection of one kidney is possible but extremely difficult to diagnose, except on post-mortem. The recommended treatment would be a long course of potentiated sulfonamides.

Secondary conditions

Primary conditions

Problems of the bladder are more common than those of the kidney; they may be related to parturition in the mare or caused by urinary stasis in the gelding through bladder stones. There will be bacteria in the urine, and also probably blood, with possible continuous dribbling of urine or total anuria in the gelding, accompanied by pain and straining; the bladder will be large when felt per rectum. A calculus may be felt in the penis, and this may either be passed following heavy sedation or removed with crocodile forceps. If the calculus is lodged at the ischial arch it may be felt just below the rectum; a catheter can be passed until the calculus is reached. If the calculus can not be removed, the animal should be humanely destroyed as there are welfare considerations with any type of urethrotomy. Naturally, cystitis should be treated with potentiated sulfonamides, provided there is some flow of urine. Bladder inversion may occur following foaling, but provided it is not torn it can be replaced under epidural, with a guarded prognosis. The mare should not be bred from again.

Secondary conditions

All cryptorchids should be castrated, and it is very important that the practitioner does not just remove the single testicle, as that will cause subsequent confusion. The gelding will often display stallion-like behaviour, even showing an erection and mounting and penetrating mares; however, in this case the owner and the practitioner may have doubts regarding the previous history of castration. If there are doubts and no testicles can be felt, blood can be taken for hormonal analysis: if the horse is >3 years of age, oestrone sulfate levels can be measured in a clotted blood sample with 100% accuracy. In the horse <3 years of age and in all donkeys, two samples are required for assessment of testosterone levels. Following the first blood sampling, the animal is injected with 6000 IU human chorionic gonadotrophin (hCG) i/v; the second sampling is then performed 30–120 min later. The testosterone level from the first sample in a cryptorchid may be confusing, as this may be similar to that for a gelding, i.e. 0.3 nmol/l; however, the second sample in the gelding will show similar values to the first, but in the cryptorchid will be markedly higher, i.e. 1–12 nmol/l.

Introduction

There are three general surgical options: (i) closed technique, where the testicle within its tunics is drawn down and removed only after the whole cord within the tunics has been ligatured, followed by suturing of the skin; (ii) semi-closed technique, which is similar but the skin is not sutured; and (iii) open technique, which is the most commonly carried out, where the tunics are incised and the testicle is drawn down so that the cord and blood vessels can be either crushed with an emasculator or ligatured, with the skin left open as in the semi-closed technique. Whether a general anaesthetic or local anaesthetic is used depends on the preference of the clinician.

The age at which a horse is castrated is very much dictated by fashion. There is no real reason why castration is not carried out in the foal, it being a myth that it will not grow into a strong, well-formed horse; it will certainly recover much quickly than the older horse, although the technique is harder as it is more difficult for the clinician to grasp the testicles within the scrotum.

Closed technique

Semi-closed technique

In some ways this method falls between two stools: it takes longer than the open method, so a relatively long general anaesthetic is required; on the other hand, as it is not locally closed there is a risk of infection and accompanying swelling, but it does lessen the risk of evisceration. This risk is low in most horses except in the case of Standardbreds and Cleveland Bays, where either a closed or semi-closed method should always be used; in fact, many veterinary indemnity insurance policies will not cover the clinician who fails to use a ligature in these breeds. Mules and donkeys in particular, when castrated over the age of 2 years, have very large vascular testicles relative to their size; there is a myth that these are more liable to haemorrhage and therefore should be ligatured, but this is not the case. Naturally, the clinician should make sure that emasculators are very strongly applied and kept in place for a minimum of 1 min. In one sense the use of a ligature in a hairy donkey poses difficulties for the clinician, as it is easy to include a hair in the ligature, which will then pull the ligature off. The advice therefore in this case must be to use the open technique.

Open technique

As this is a relatively simple technique surgically, it can be done standing under local anaesthetic and sedation. However, there are welfare considerations; if the horse is very well handled and is above 15 hands then this technique may well be the method of choice. After the tail has been bandaged, the horse is sedated and a twitch is applied. The scrotum is checked to see that it contains two testicles and that there is no evidence of an inguinal hernia. The scrotum is washed thoroughly with a dilute chlorhexidine solution and 10 ml local anaesthetic is injected into each cord. Another 10 ml of local anaesthetic is then infiltrated along the ventral aspect of the scrotum on both sides where the incisions are going to be made. The area is rewashed.

Careful instructions and warnings are given to the horse’s handler; ideally, castration should be performed in temperate climates in the spring or autumn, when keeping the newly castrated colt outside is not a problem either on account of flies or very inclement weather. However, if the colt has to be castrated in winter, it must already either be living outside, even at night, or a closed castration method used. In warmer climates the horse should not be allowed into any stable or shelter for 10 days, to lessen the danger of sepsis. The handler must be told that swelling of the scrotum and prepuce are inevitable. If either severe haemorrhage occurs or a piece of tissue that the horse can not retract is seen, the handler should contact the clinician. The use of antibiotics and NSAIDs is up to the discretion of the clinician. However, all horses not fully immune to tetanus should receive tetanus antitoxin.

Introduction

As stated earlier, it is important that all rigs are castrated, as this is an inherited condition. It is also very important that practitioners do not remove the single testicle if a unilateral rig is presented. Planning is everything with this surgical procedure, and it is very important that the surgeon knows all the facts before the anaesthetic is administered. The horse that is presented may have no testicles in the scrotum – it may already have been castrated, and in this situation a hormone test, as already outlined above, should be carried out. If this shows the horse to be a rig, the clinician has no way of knowing for certain whether there are one or two testicles in the abdomen. Horses have been described having been born without one or both testicles, but such cases are extremely rare and will not test positive to the rig test. Some clinicians are able to palpate an abdominal testicle near to the inguinal ring per rectum.

Fig. 17.1. Castration performed under general anaesthesia.

Castration of the rig is a very difficult and highly skilled procedure. A 5 MHz linear scanner is quite useful to visualize a testicle near to the inguinal ring. Abdominal testicles, of course, can be found and removed by endoscopy. However, assuming these sophisticated aids are not available, the clinician has to rely upon common sense. One of six different scenarios is presented to the clinician:

1. If the animal has one normal testicle in the scrotum and a second palpable in the inguinal ring, the respective sides should be noted. Although this animal is a rig, it is likely that with a good general anaesthetic (GA) both testicles can be removed. The surgeon should remove the testicle in the inguinal ring first but, if that can not be removed, on no account should the normal testicle be removed. There is no need to carry out a rig test.

3. If the animal has one normal testicle in the scrotum and no testicle can be felt in the inguinal ring on the other side, it should be examined for scars. If there is a scar, this scar must be examined carefully; if the scar is just under the skin, the animal is definitely a rig, the side of the normal testicle is noted and rig surgery will need to be carried out. There is no need to carry out a rig test. If the scar is attached to a deep structure not just beneath the skin, the animal is unlikely to be a rig because one testicle is likely to have been removed previously. The side of the normal testicle should be noted and normal surgery to remove that testicle will need to be carried out. If after a few weeks the animal stops showing stallion-like behaviour, there is no need to carry out a rig test. On other hand, if the stallion-like behaviour persists then a rig test should be carried out. If this test is positive then the side with the earlier scar will need to be investigated.

4. If the animal has no normal testicles in the scrotum but two testicles can be felt in the inguinal rings, it is a rig. However, with a good GA it is likely that both testicles can be removed. There is no need for a rig test.

5. If the animal has no normal testicles in the scrotum and one testicle palpable in the inguinal ring, the side of this testicle should be noted. This animal is a rig. At this stage a rig blood test would not be appropriate, as the practitioner already knows there is a testicle, albeit abnormal, present. On the other hand, appropriate surgery should be carried out. The side without the palpable testicle should be investigated for scars. If there is a scar with adhesions deeper than the skin, it is likely that the testicle on that side has been removed. The surgeon can then remove the other testicle with some confidence. If after some time stallion-like behaviour persists, a rig test should be carried out, and if this is positive then further surgery will be required to investigate the side where no previous testicle was located.

6. If there are no testicles in the scrotum and no evidence of scars, then the animal is likely to be a bilateral rig. It is prudent to carry out a rig test to make sure that the horse actually has testicles.

Inguinal approach

The vaginal tunic is next grasped by a pair of long-handled forceps. A small incision will reveal the deferent duct, which becomes the epididymal tail distally and returns up the lumen of the vaginal tunic as the epididymal body. These two structures, the epididymal tail and body, can be recognized as they consist of coiled tubes, the tail consisting of a large tube loosely coiled, with the body a fine tube tightly coiled. With a pair of long-handled forceps similar to whelping forceps but narrower, traction is applied to the body of the epididymis. The opening in the vaginal tunic may have to be enlarged, but the testicle should be able to be drawn out. The vessels are ligatured and the testicle removed. This procedure should be repeated on the opposite side.

The main problem with this method is seen when the abdominal testicle is not small and flabby like a normal abdominal testicle, but large and cystic. The inguinal ring has to be enlarged to allow exteriorization of this enlarged structure, and it is then difficult to close the inguinal ring. Many mattress sutures should be laid in place before tightening up. A substantial layer of subcuticular sutures should be put in place before the skin is closed with horizontal absorbable mattress sutures. The horse, if possible, should have an assisted recovery and be kept in a small area for 10 days to allow the area to heal. Antibiotics and NSAIDs are given to lessen infection and swelling.

Should one testicle not be found, the inguinal ring should be closed as described above and the horse allowed to recover. A second rig test is next performed to confirm that there is still a testicle present. The horse will then have to be re-anaesthetized and a paramedian approach, as described below, performed.

Paramedian approach

Closure of the transverse tendon and abdominal tunic and closely adherent tendons of the external and internal oblique muscles is made with a single cruciate suture of thick Vicryl^®. Great care is needed to ensure that no small intestine is trapped in this suture; however, once this is tightly tied the surgeon can relax, since small intestinal prolapse is then impossible. The outer abdominal tunic can be sutured with interrupted horizontal mattress sutures. The dead space is filled with the subcuticular sutures aligning the tissue and the skin is closed with interrupted horizontal mattress sutures of absorbable material.

Testicular torsion

The main presenting sign here will be acute colic; the differential diagnosis is a strangulated loop of small intestine in the inguinal ring. The differentiation is not easy – the technique is very heavy sedation and pain relief, and then the scrotum – and particularly the inguinal ring – can be examined thoroughly. In either event surgery is required. It is conceivable that hemicastration could be performed under heavy sedation and local anaesthesia, but a general anaesthetic is more prudent.

The scrotum and surrounding area are surgically prepared. A very careful incision is made over the testicle through the skin. The tunic should be incised only after careful examination; if there is no evidence of the presence of either bowel or omentum, the testicle can be removed as for an open castration. If there is bowel present it should be examined carefully for viability, and if all is well it can be returned to the abdomen; if in any doubt, a resection must be performed before returning the bowel to the abdomen. In either case the inguinal ring may have to be enlarged. Mattress sutures require to be laid before any are tightened, then the subcuticular layer closed, before suturing the skin. All layers must be sutured with absorbable material. Antibiotics and NSAIDs are necessary.

Orchitis

Equine viral arteritis

A disease found worldwide, the stallion is the carrier. The mare can become infected at coitus or from artificial insemination (AI); equally, the mare can become infected from aborted fetuses or horses having the respiratory form of the disease. The incubation period is 3–8 days. Normally, the signs are of a mild respiratory infection; however, if abortion occurs these may be more severe, with fever and oedema of the udder and hind legs. The disease is self-limiting, excepting that stallions remain as carriers. Diagnosis is by serology, although it is impossible on a single sample to separate an infected animal from a vaccinated one; paired samples with a rising titre are required to confirm active disease. Care should be taken when vaccinating a horse that may be exported – a blood sample showing a negative titre should first be obtained.

Coital exanthema

Often classified as a skin disease, this condition is caused by equine herpes virus-3. It is found throughout the world and is spread mainly by coitus. However, veterinary instruments have also been blamed, so the clinician should be ever mindful of disease control. The incubation period is 1 week. The vulva and the penis will develop herpes blisters, which turn into sores; these will heal in a further week but may leave permanent skin pigmentation deficits. There will be a breeding delay, but no permanent problem.

Contagious equine metritis (CEM)

Other bacterial conditions

Included here are Pseudomonas aeruginosa, Klebsiella pneumonia, Escherichia coli and Streptococcus zooepidemicus. These all will cause infertility in the mare and are likely to be spread venereally; however, only certain K. pneumonia strains possessing a K capsule are entirely venereal. All these organisms may be found as normal flora on the skin; it is only when they are present in large numbers that disease occurs. It is important that the stallion’s penis is not washed in iodine or chlorhexidine, as those disinfectants will help promote the growth of these organisms; the penis should be washed regularly with simple, non-perfumed soap.

Dourine

The stallion has four accessory glands: a pair of ampullae, a pair of seminal vesicles, a bilobed prostate and a pair of bulbourethral glands. Diseases of these glands are extremely rare and these are likely to go unnoticed except when semen is collected, when the semen may be blood-tinged or will culture positive for S. zooepidemicus, K. pneumonia, P. aeruginosa or Staphylococcus aureus.

Infection and inflammation

The potentially dangerous sequel is prolapse or paralysis of the penis. If the penis can not be returned into the prepuce, this condition is called a paraphimosis. There is also a congenital condition where the penis can not be extruded, termed phimosis, which can be corrected by widening the preputial orifice. Antibiotics and NSAIDs are insufficient treatment for paraphimosis, because the oedema of the penis will be self-perpetuating. It is vital that the penis is supported, the best support being a pair of nylon tights tied over the back and anchored by bandage to the tail head.

The penis may be affected in habronemiasis (often called ‘summer sores’), initiated by the nematode Habronema; the horse should be treated with oral ivermectin at 0.2 mg/kg, as well as soothing, oily cream locally.

Tumours

Squamous cell carcinoma

Frequently, this will be well advanced before being noticed. If the penis alone is affected, amputation should be carried out as described below; however, if the prepuce is also involved the condition should be managed as well as possible, with euthanasia being carried out terminally.

Melanoma

Occurring only in the grey horse, often this will grow very slowly and so the horse will be able to live out a natural lifespan. However, if it ulcerates or is colonized by maggots, euthanasia is the only option since removal is very rarely successful in the long term.

Viral papilloma

Sudden onset is seen in the young horse, and equally suddenly will disappear without treatment. However, the clinician should be wary of such papillomata in horses over 6 years of age – these may well not be papillomata but equine sarcoids (see below).

Equine sarcoid

Equine sarcoids at this site are very hard to treat. Very sophisticated treatments, e.g. laser or cryosurgery, are available, but simpler treatments may be just as affective if the cases are chosen with care. If the sarcoids are multiple and very invasive, the animal should be euthanized but, if pedunculated, either a rubber elastrator ring or a very tight, non-absorbable ligature can be placed around the neck of the mass. Another course of treatment is to inject, normally under GA, a cytotoxic substance, e.g. 5-fluorouracil, into each sarcoid.