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Clinical approach to castrationin the donkey

Description
This dichotomy can bring about clinical challenges rarely seen with other species. Although most conditions affecting donkeys are similar to those occurring in horses,donkeys by their very nature can behave differently in the face of disease. Hence, some clinical presentations that would ordinarily be dismissed in other equids must be considered as medical/surgical emergencies in the donkey. This article, the first in an occasional series discussing the clinical approach to problems in the donkey, describes the options for castration, and offers practical advice on how to avoid some common pitfalls and potentially fatal complications that are specific to this species.



Timing of castration

Surgical castration carries more potential hazards in donkeys than in horses or ponies. However, with forward planning and selection of the most appropriate procedure, there is no reason why the surgery should not be successful.
Ideally, castration of the male donkey should be carried out when the animal is between six and 18 months of age. Some young male donkeys can start to demonstrate undesirable sexual behaviour at five or six months of age. This can make life miserable for the dam or any other animal unfortunate enough to be kept in his company and also establishes behaviour patterns that will prove difficult to break even after castration. Older entire donkeys may be aggressive to companion geldings and hard to control around mares.
As with any equid, castration should be avoided in the fly season.




Preoperative assessment

A preoperative assessment allows the clinician to evaluate the animal prior to surgery and select the most appropriate anaesthetic and surgical approach. It also provides a good opportunity to discuss the options for castration with owners and involve them in the decision-making process. It is important that owners understand that castration in donkeys can be a more complicated
procedure than in horses and ponies. The clinician should therefore explain the potential problems associated with each technique and how these might be overcome.
Donkeys, frequentlychange ownership and their past veterinary history is not always passed on to subsequent owners. This should become less of a problem with the advent of equine passports.
Nevertheless, where possible, the clinician should attempt to obtain a good history. In particular, information about the donkey's tetanus vaccination status should be sought and, if there are any doubts over an animal's prophylactic history, it should be given tetanus antitoxin prior to surgery as a matter of routine.
A thorough physical examination of the inguinal region should be carried out to reveal potential hazards such as cryptorchidism and hernias. If only one testis is present, the animal may be cryptorchid (rig) or have been castrated previously when only one testicle had descended adequately. Scrotal scarring may indicate previous surgery. Rigs can be confirmed using a dynamic chorionic gonadotropin stimulation test.

Chorionic gonadotropin stimulation test
Suspected rigs should be tested for levels of testosterone, irrespective of their age. Two serum (clotted blood) or heparinised blood samples should be taken for testosterone measurement:
  • The first, prior to the intravenous injection of 6000 iu human chorionic gonadotropin;
  • The second between 30 and 120 minutes after the injection.

    The preoperative clinical examination should include a biochemistry and haematology profile. Donkeys are very stoical creatures and even young fit animals can often mask diseases, such as pancreatitis, hyperlipaemia or hepatic dysfunction, all of which can seriously compromise a successful surgical outcome.

    Respiratory function should also be examined carefully. Donkeys are mostly non-performance animals and can survive with significant subclinical lung pathology, which may only come to light under anaesthesia. The preoperative assessment is also a good time to consider the practicalities of the operation and again discuss the options with the owner. If the animal is to be stabled perioperatively, ensure the accommodation is suitable and that there is a supply of non-edible bedding. Donkeys need close post-surgical monitoring (see later). If the patient has a closely bonded companion, the two animals should be kept together if possible until induction. The use of sedatives should be considered for the companion.
    If the need for castration is not acute (ie, it is not close to the start of the fly season or mares are not being moved into the stallion's territory imminently), it is worth advising owners to teach the donkey to walk-inhand before surgery. A surprisingly high number of donkeys are unhandled and, as postoperative care invariably involves walking-in-hand, this accustomisation to being handled has immense physical benefits for the animal in the post-surgery recovery period.

    Preoperative checklist
  • Conduct a pre-anaesthetic health check, including tetanus status
  • Obtain biochemistry and haematology profiles
  • Select suitable non-steroidal anti-inflammatory drugs and antibiotic regimens
  • Select anaesthetic protocols and surgical technique
  • Discuss complications, postoperative care and compliance with owners
  • Initiate walking-in-hand practice
  • Ensure provision of suitable perioperative accommodation, feed and nursing care




    Methods of castration

    The following surgical approaches can be used for castrating
    donkeys:
  • A. Closed technique;
  • B> Semi-closed technique: a)Via a scrotal approach; b)Via a cranial inguinal approach.

    Each of these methods has advantages and disadvantages,so the optimal approach must be chosen based on the size, demeanour and age of the donkey, and the surgical experience of the clinician
    It should be noted that for all surgical procedures involving donkeys there must be adequate personnel to assist the surgeon with the administration and monitoring of the anaesthetic, and to provide general assistance. This requires a qualified nurse or second veterinary surgeon and is not a suitable role for the owner. Standing castration performed under sedation is not recommended, as the height of the donkey, the need for safe ligature application and good visualisation of anatomical structures all necessitate general anaesthesia.




    A. Closed Technique

    The term 'closed' refers to the fact that the parietal tunica vaginalis is not opened, and hence no direct access to the abdominal cavity is achieved. This is the method of choice for young, slim donkeys. It is not suitable for larger, older animals that have significant deposits of scrotal fat or donkeys that are sexually mature. This is probably the only technique that can be performed
    just as adequately in the field as in the operating theatre, although it requires a general anaesthetic with good relaxation in both environments. An example anaesthetic protocol that has been successfully used for donkey castrations in the field is highlighted below.(surgeon preference may dictate an alternative approach).
    The surgery time is generally longer than for the simple open castration often performed in horses, and donkeys will usually require top-up doses of anaesthetic agents if an alpha2-agonist/ketamine combination is used. The procedure is also more complicated and time consuming, especially if the surgeon is inexperienced in the technique.
    Once anaesthetised, place the donkey in lateral recumbency with the uppermost hindleg tied to expose the surgical area. Clip and surgically prepare the site, and inject 3 to 10 ml of local anaesthetic into each testis in the direction of the spermatic cord using an appropriate length needle. This allows for greater relaxation and subsequently better exposure of the cord. Operate on the lower testis first to ensure good visualisation of the second. Incise the skin without incising through the tunica vaginalis communis. Clear any fat deposits by blunt dissection using dry swabs to obtain an adequate grip. Such fat deposits can cause wicking of infection. Once the spermatic cord and cremaster muscle are exposed, a scrubbed up assistant should hold the testis while the ligature is placed. Care should be taken at this stage not to pull excessively on the cord as this can cause the vessels to retract inside.
    Place one 5 metric absorbable suture around the cord and tighten slowly. This may be anchored in the cremaster muscle or placed as a transfixing ligature. Some clinicians recommend using two ligatures for security, but there is evidence to show that the placement of the more distal of the two ligatures can cause necrosis and infection, which can then track back up the cord. There
    is also an increased risk of a foreign body reaction. One adequately secured ligature should be sufficient.
    Attach tissue forceps to the proximal part of the cord before applying an emasculator 2 cm distal to the ligature. Leave these in place for two minutes (an assistantshould measure this time accurately). Remove the emasculator and check for haemorrhage by allowing the cord to retract slowly before removing the tissue forceps. The procedure is then repeated on the second testis
    and the wounds left open to heal by second intention.

    Anaesthesia protocol for castration in the field
  • Conduct a standard preoperative assessment
  • Administer tetanus antitoxin, antibiotics and non-steroidal anti-inflammatory drugs, as required
  • Use acepromazine at 0·03 mg/kg intramuscularly to calm fractious animals 30 minutes prior to surgery, if time permits
  • Place a jugular intravenous catheter under local anaesthesia or soon after the administration of the alpha2-agonist in fractious individuals. This will allow the anaesthetic to be toppedup and maintained, as required
  • Administer an alpha2-agonist (eg,xylazine) at a dose of 1·1 mg/kg. After five minutes, administer the induction agent. Ketamine (2·2 mg/kg) may be combined with diazepam (0·01mg/kg) or midazolam (0·01 mg/kg) to improve relaxation
  • Infiltrate local anaesthetic (5 to 10 ml lidocaine) into each testis and up into the cord
  • Prolong anaesthesia using topup agents, which should be ready to hand with a suitably trained person



    Recommended triple drip

    Donkeys are more sensitive than horses to guaifenesin so the recommended triple drip combination for donkeys is produced by:
  • Removing 200 ml from a 500 ml bag of saline;
  • Adding 150 ml of 15 per cent guaifenesin, 225 mg xylazine and 900 mg ketamine.
    This will make about 500 ml of donkey triple drip formula, which can be given at 1 ml/kg/hour, and may be used after premedication with xylazine.




    B. Semi-Closed Technique

    The semi-closed technique is useful for mature jacks with well developed testes and large deposits of scrotal fat as well as for donkeys that are sexually active. As mentioned earlier, such animals rarely cease sexual behaviour following castration - in many ways, this is a learned behaviour and the animal continues to behave as a stallion even after the testes have been removed. The semi-closed technique involves incising through the parietal tunica vaginalis and securely ligating its contents. Given that the abdominal cavity is accessed, there is an increased chance of eventration, so security of the ligatures is of paramount importance. There is also a greater risk of introducing infection via this method and a high degree of asepsis is required. This technique
    should only be carried out within a hospital environment.

    Semi-closed castration via the scrotal approach
    This approach allows for more secure haemostasis than the closed technique. It is suitable for quiet and/or sexually inactive adult jacks, which can have significant deposits of fat within the cord and well developed vaginal tunic fascia.The donkey is prepared as for the closed technique, but can be placed in lateral or dorsal recumbency. Infuse the local anaesthetic through the testes in the direction of the cord. Note that there is a significant blood supply to the scrotum in mature animals, so the surgeon should be prepared to perform diathermy or ligation of the many vessels in the area.
    As with the closed method, incise the scrotal tissue, but this time continuing the incision through the tunica vaginalis communis. Locate and ligate the neurovascular bundle with 5 metric absorbable suture material, emasculate or transect distally, check for haemorrhage and allow the bundle to retract back up the vaginal process. As before, place artery forceps on the proximal stump to check for haemorrhage following ligation, and remove them if no haemorrhage is seen. Emasculate the remaining vaginal process as proximally as possible. Fat and fascia act as foci for infection, which will track back up the cord, and should therefore be removed. Again, the scrotal skin is left to heal by second intention. Surgical closure usually results in unacceptable swelling and is not recommended.

    Semi-closed castration via the cranial inguinal approach
    This method is most suitable for large, sexually active jacks, as there is less opportunity for postoperative infection associated with their continuing sexual activity. It is quite common for these animals to try to mount their companion animal immediately on returning from the recovery box! In these situations, they force further lengths of vaginal process down the inguinal canal which can lead to
    extensive and, in some cases, life-threatening infections.
    This approach allows the skin incisions to be closed. The disadvantage of this procedure is an often high degree of swelling and discomfort. It is best to make longer incisions to allow the easy removal of the testes rather than to struggle with too small an incision only to increase the time taken for what is already a lengthy procedure. Any unnecessary handling of local tissues leads
    to increased inflammation and increased postoperative recovery time. Closure of dead space can help minimise postoperative swelling. See Du Preeze (1999) and Green (2001) for further information.
    Place the animal in dorsal recumbency and surgically prepare the site. Make an incision over the external inguinal ring and locate the spermatic cord by digital palpation and withdraw it through the ring. Use gentle but firm traction to withdraw the testes through the incision, thereby everting the scrotum. Divide the scrotal ligament to free the testes. Locate, separate and ligate the cremaster muscle.
    Incise the vaginal tunic and ligate the contents, as described above for the other techniques, and return the stump to the tunnel of the vaginal tunic. Ligate the whole cord and sever the vaginal process to remove the testis, epididymis and the remaining tunic. Close the skin using absorbable sutures. As mentioned, this method of castration can produce a high degree of swelling. The donkey will need two days' box rest, followed by diligent walking-in-hand at least two or three times daily for the next week.




    General Anaesthesia Considerations

    The placement of an intravenous catheter for the provision of general anaesthesia is essential for all three castration procedures, but may be more difficult than in the horse due to the thicker cutaneous colli muscle and subcutaneousfat. Standard doses of sedatives and induction agents may be used, but will need to be increased to effect in unhandled or stressed animals. A closed in-field castration will require top-up doses of anaesthetic as donkeys will not remain anaesthetised for long enough after induction.
    Intubation can be difficult in donkeys due to the narrow larynx, so a range of sizes of endotracheal tube from 14 mm (for miniature donkeys) to 20 mm (for large donkeys) should be available. The average sized animal will require a 16 mm tube. For further information on appropriate anaesthesia protocols in donkeys, see Matthews and Van Dijk (2004).




    Postoperative Care

    Postoperative care is crucial to the successful outcome of castration in donkeys. Owners should be informed about the general care of the animal as well as the problems to look out for, including the degree of swelling that can be expected and how to assess pain or discomfort. If the donkey has been hospitalised for surgery, it may be worth keeping the patient and its companion (if it has one) under the judicial eye of in-house nurses, if possible. On the whole, if a donkey does not have to move, it will not! This predisposes it to postoperative oedema and associated discomfort. If donkeys are uncomfortable, they stop eating, which in turn predisposes them to lifethreatening conditions such as hyperlipaemia and intestinal impactions. Non-steroidal anti-inflammatory drugs can also mask signs of abdominal discomfort. Monitor food intake and faecal output closely for the week following surgery. If the donkey is being stabled with its companion, it may be necessary to perform fre-quent rectal examinations to make sure the patient is passing faeces. Gut sounds should be monitored regularly and any depression in appetite should be taken seriously. Check the animal’s plasma triglyceride levels; signs of serum cloudiness once a clot has formed are indicative of hyperlipaemia.
    Donkeys should be housed with non-edible bedding, and bran mashes and chopped forages introduced to reduce the risk of colonic impaction. Hospitalisation and the stress of environmental change can also affect the patient’s companion; it is very easy, even for experienced clinicians, to concentrate on the primary patient while its mate quietly shows signs of hyperlipaemia or colic.
    Diligent walking-in-hand is probably the most positive task that owners/grooms can perform following castration in donkeys. As mentioned earlier, it is important to accustomise the animal to walking-in-hand before surgery, and the beneficial effects of this simple exercise should not be underestimated.

    Postoperative care checklist
  • Depending on the technique used, the subsequent swelling and the housing provided, carry out walking-in-hand exercise four or five times daily for at least seven days for stabled animals
  • Closely monitor food intake, faecal output and general demeanour. Take blood samples if hyperlipaemia is suspected
  • Provide non-steroidal anti-inflammatory drugs

    Use of non-steroidal anti-inflammatory drugs in the donkey
    Non-steroidal anti-inflammatory drugs should be used as a matter of routine in all donkeys undergoing castration. However, donkeys are frequently underdosed in practice because dosing guidelines for ponies have been used. This is due to the fact that donkeys and horses have different rates of metabolism, and thus require slightly different dosing regimens to provide more effective analgesia. General guidelines regarding safe use should be adhered to, especially in very young, old or otherwise dehydrated, hypovolaemic patients.

  • PHENYLBUTAZONE is cleared approximately twice as fast in donkeys than in horses (possibly even faster in miniature donkeys). Administer at twice the dosing frequency (eg, 2·2 to 4·4 mg/kg twice daily)
  • FLUNIXIN MEGLUMINE is also cleared around twice as fast in donkeys than horses. Administer at twice the dosing frequency (eg, 1·1 mg/kg twice daily)
  • SUXIBUZONE is metabolised to phenylbutazone and oxyphenbutazone, and there are likely to be differences between donkeys and horses in the rate of this metabolism. However, there is no research information available
  • KETOPROFEN is cleared more rapidly in donkeys and has a higher volume of distribution. More frequent dosing is therefore likely to be required (eg, 2·2 mg/ kg twice daily)
  • CARPROFEN is cleared about three times more slowly in donkeys than in horses, which suggests that a rate of 0·7 mg/kg once daily should provide adequate analgesia in donkeys
  • MELOXICAM has been shown in limited studies to have 1/10 the half-life in donkeys compared with horses. Donkeys therefore require very frequent administration to achieve adequate analgesia




    Complications of Castration Procedures

    Irrespective of how experienced the clinician is or how prepared handlers are, complications inevitably arise from time to time. Owners should be forewarned about any possible problems. If operating in the field, it is good practice to be prepared for the worst by ensuring that extra sterile packs, fluids and anaesthetics are available should an emergency arise.

    Haemorrhage
    Haemorrhage is the most immediate complication, arising either instantly following recovery or up to 24 hours after surgery. The origin of the haemorrhage may be the external pudendal vessels, the testicular artery or the large scrotal vessels. Pressure bandages secured by elasticated bandages and the administration of a sedative to calm the animal have been used to stem what initially
    appeared to be a dramatic arterial bleed although, in hindsight, this was probably an exceptional case.
    If a haemorrhage occurs, it is crucial that the donkey is re-anaesthetised as soon as possible. The animal must be assessed for blood loss and haemorrhagic shock, and treated accordingly. Once anaesthetised, the scrotal wound should be cleared to allow the offending vessel to be located and religated.
    It is sometimes impossible to locate the origin of the haemorrhage and, while this can be very distressing, the situation is not always irretrievable. Packing the wound, keeping the animal's blood pressure low and instituting a blood transfusion can often be enough for an animal to claim control over its own haemostasis and make a complete recovery.

    Infection
    Infections can be superficial or deep, with the latter involving the tunica vaginalis and scirrhous cord. Wounds should be monitored carefully two or three times a day and any suspicion of infection investigated under sedation using a gloved hand. A swab for culture and sensitivity testing should be taken at this stage. Local infections can usually be dealt with by enlarging the incision site to improve drainage and cleaning with dilute povidone-iodine solution. The animal should already be undergoing antibiotic therapy, but it may be necessary to change preparations to treat the infection.
    Deep infections may lead to champignon formation or scirrhous cord infections, which require resection under general anaesthesia. Owners should be made aware prior to repeat surgery that scrotal ablation may be necessary if scrotal tissue is infected. Repeat surgery such as this should not to be undertaken lightly and should not be carried out in the field. Referral to hospitalisation facilities
    is strongly recommended.

    Eventration
    Eventration is unlikely following closed castration, although small pieces of fat and fascia may prolapse out of the wound. These tissues should not be ignored as they can be a nidus for infection, and can be cut away under sedation, if necessary. Larger scale eventration should, however, be dealt with under a repeat anaesthetic. These problems can easily turn nasty if given the opportunity.
    Any suspicion of eventration following a semi-closed castration should be taken seriously and the animal immediately referred to a specialist hospital.

    Excessive Swelling
    Excessive swelling is a problem in donkeys due to their propensity not to move unless they have to. The need for compulsory walking-in-hand exercise cannot be overemphasised. Hosing the area should be avoided as this can seed infection up into the tissues and increase general waterlogging of the area.

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