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American Mammoth Jackstock
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Table of Contents
Introduction
Historical Significance of the Donkey
Restraint Techniques for Donkeys
Observations Regarding the Musculoskeletal System
Jack Sores
Colic in Donkeys
Surgery
Introduction
The following segments of this text are observations of Jackstock breeding, training, and showing over the past thirty years. Most of it is personal observations and observations noted from others’ experience with the breed. The opinions are based on information available at this time. Regrettably, these topics have not been scientifically tested or otherwise evaluated. They are presented for the consideration of the reader and hopefully each will be substantiated, expanded, modified, or deleted as valid information comes available. In general, we expect that observations made on one size donkey group would be reasonably applicable to other sizes. It seems reasonable, however, that this is not always the case. The following observations were primarily based on experience with Mammoth donkeys.
In the United States, a size classification is used rather than a breed designation when describing donkeys. For the benefit of the reader this size classification is provided below along with some common terms that may be confusing to people not familiar with the American donkey industry.
Donkey - Common name used worldwide to refer to species in the ass family.
Jack, Jackass, Jack Ass - Intact male in the ass family.
Jennet, Jenny - A female in the ass family.
Burro - Smaller members of the ass family. These may be of Mexican or Spanish stock and are usually gray in color. This term is usually applied to a feral ass.
Donkey Gelding or Gelded Jack - A castrated male of the ass family.
Mule - The hybrid cross resulting from breeding a jack to a mare (horse).
Hinny - The hybrid cross resulting from breeding a stallion (horse) to a jenny.
Mare Mule - Female mule, may also be referred to as a Molly mule.
Horse Mule - A male mule, often referred to as a John mule.
Mare Hinny - A female offspring as the result of breeding a stallion (horse) to a jenny.
Horse Hinny - A male offspring as the result of breeding a stallion (horse) to a jenny.
Mule Mare - A mare (horse) used to raise mules.
Miniature Donkey - A member of the ass family that stands at 36 inches or less at the withers when mature.
Standard Donkey - A member of the ass family who, at maturity stands more than 36 inches but less than 56 inches at the withers. This group may be divided into small standards, standards, and large standards.
The American Donkey and Mule Society | |
Small standard | under 40 inches |
Standard | under 48 inches |
Large standard (jennets) | under 54 inches |
Large standard (jacks & geldings) | under 56 inches |
Mammoth Donkey - A member of the ass family who, at maturity complies with the following regulations of each breed registry.
Mammoth Jackstock Regulations | The American Donkey and Mule Society | ||
Jacks | 8 inches | Jacks | 56 inches |
Jennets | 56 inches | Jennets | 54 inches |
Jackstock - A term used to indicate multiple animals of mammoth size including both sexes.
Figure 1. A good example of an American Mammoth jennet standing 58 inches tall (approximately 147.3 cm).
Historical Significance of the Donkey
The American Mammoth Jack or American Mammoth Jackstock of today has a very unique history in its breed development. There are several books and websites [1,2] available that chronicle the details of this historic progression beyond the scope of this chapter. The American Mammoth Jackstock evolved as mule sires following the end of the Revolutionary War and continued to approximately the second quarter of the twentieth century. This evolution resulted from the need for animal agricultural power in a post-war economy. The Jackstock of today are the results of renewed interest in the breed starting in the 1960s or early 1970s and this interest in Jackstock has become more recreationally oriented in comparison to their ancestors. This same statement is true for mules of the present and foreseeable future.
In contrast to most breeds of livestock, the American Mammoth Jack is an unquantifiable combination of many other donkey breeds. The primary breeds of larger Asses contributing to this development were the Maltese, the Poitou, the Andalucian, the Catalonian, and the Majorcan [3,5]. The Poitou is from France and the other four breeds are considered to be of Spanish origin [3]. The Catalonian breed is thought to be the greatest contributor of all the breeds to the American Mammoth Jackstock [5]. History suggests that when crossed with each other and on American soil, many of the offspring grew to sizes and developed qualities greater than their imported ancestors. At the peak of their production, the following was considered to be the characteristics of a good American Mammoth Jack.
The conformation measurements of an American Mammoth Jack are as follows: | |
Ears from tip to tip | 34 inches |
Around the face and jaw | 39 inches |
Around the neck at throatlatch | 36 inches |
Around arm | 21 inches |
Around cannon | 8.5 inches |
Length from poll to tail | 84 inches |
Around body at loin | 67 inches |
Height | 62 inches |
The inability to uniformly control or standardize the specific contributions made by the different ancestral breeds was a result of many factors. These factors included widespread need for mules within a developing country lacking in communication capabilities and different farm needs in different geographical areas. There was not an unlimited supply of animals available for purchase and importation as the country flourished. Very little is known about the genetics of the donkeys in the USA present at this time, but it is unlikely that they were closely related to the animals being imported. In spite of the diligent application of sound breeding techniques by dedicated stockmen, genetic diversity has always remained within the breed. Today, genetic diversity may be more prominent than anytime since the beginning of the initial breed organizations.
Like those of horses and mules, the Jackstock numbers dwindled during the period of the advent of the internal combustion engine and its adaptation to provide many types of agricultural power. This transition from animal power to mechanical power occurred at different times in various geographical regions and for different purposes. The transition loosely spanned a period from 1920 to about 1950. Only a handful of Jackstock breeders remained. Few people expected work-stock to ever again be economically justified after the introduction of mechanical power into agriculture. It is likely that those remaining few Jackstock breeders, out of love for the breed and sentimental attachment for preserving the past, kept the breed from extinction.
Mammoth Jackstock, like other members of the equine species returned to prominence shortly after the midpoint of the twentieth century and are exponentially increasing in numbers today. As this new interest in Jackstock developed several events occurred that markedly affected the gene pool of today’s Mammoth Jack. Some of the events are presented here, but are not in order of importance or chronology. In what is presumed to be an effort to facilitate the growth in numbers and perhaps broaden the genetic base, some of the breed requirements were relaxed. Lowering the size requirements was one of the most notable compromises.
New registries have been formed and as of today there are at least six that register Mammoth donkeys; one is the original Jackstock registry. All the registries are open as of this date and this, along with classification of the donkeys by size rather than breed or pedigree, has opened the Mammoth donkeys to an onslaught of color patterns, sizes, and gene pools. Although we can accept that such decisions were made based on what people at the time felt was best for the breed; time may demonstrate that the toll of diversity, by opening the registry, has only aided in demise of the true genetic characteristics of the breed. There are ongoing efforts among some individuals to accumulate breeding stock with the greatest relationship to the Mammoths of the past in hopes of preserving or closely reproducing the older Mammoth stock.
As we mourn the past, we must celebrate the future of the breed. The Mammoth Jackstock of the past was bred to produce mules for work. The Jackstock was not athletic in terms of how we use donkeys and mules today. In short, they would have limited use in the production of recreational mules and donkeys for today’s equine enthusiasts. The reality is that our livestock must adapt to new uses in order to make adequate contributions to society to justify their existence. Jackstock of today must have the eye appeal and athletic ability to perform as recreational animals and not just mule sires, or their mule offspring must meet these expectations. Without these qualifications, we would only see American Mammoth Jackstock in zoos or special collection facilities. Let’s hope with the help of veterinarians and breeders that this breed will continue to adapt to the uses of the equine world for many years to come.
Restraint Techniques for Donkeys
Many donkeys are accustomed to being handled and managed by people. Those that are well trained and disciplined usually do not require special restraint in order for the veterinarian to carry out common veterinary diagnostic and therapeutic procedures. Presently, it is quite unfortunate that in most recreational donkeys, these characteristics are the exception rather than the rule. Thus, the equine veterinarian is often forced to restrain donkeys that are unaccustomed to human interaction or have not been taught to respect their handlers. The smaller the donkey, the more difficult it seems to be to utilize many of our physical restraint techniques. Much like the horse, there are an almost innumerable number of applications and techniques that are described to facilitate working with donkeys. This section will address only a few techniques that have been useful in the experience of the authors. There is no doubt that others will also have favorite and different methods of restraint.
As a prelude to describing restraint procedures, it is important to evaluate some of the characteristics of the donkey that may influence their responses to being restrained. Horses are commonly considered to be "fright and flight" animals. The horse’s best defense, like most prey animals, is to flee from harm. Donkeys are also in the category of prey animals, but many times the majority of donkeys when threatened by a frightful situation will "freeze up" or pause and remain still to assess the situation. Any decision they make to flee is often not immediate. The donkey, however, frequently decides that flight is the best option. This escape attempt may take the form of immediate and perhaps uncontrolled flight or it may be a slower more deliberate departure. This is a significant point to remember when restraining donkeys. If we can prevent them from making early aggressive attempts at flight we are getting the advantage in controlling the animal. This does not imply that is easy to restrict the slow deliberate departure of a donkey by the use of a lead rope, twitch, or similar restraint tool. Even a small to average size donkey can often slowly wander off with one or two handlers while a twitch, lead rope, war bridle, or chain shank is being used unsuccessfully as a restraint tool. Veterinarians and handlers alike must therefore look upon donkey restraint as a two-part procedure.
The first issue in proper donkey restraint is to ensure that the donkey does not have the ability to leave the area where you plan to perform the examination or treatment. This includes physical means of confinement and closing visual pathways for departure. In short, the use of small pens, equine stocks, portable panels, well-made halters, strong lead ropes, and snubbing posts frequently eliminate the animal’s expectations of escape and may be all that is required to warrant cooperation.
The second phase of restraint is a technique to distract the animal’s attention from or elicit the cooperation of the animal to perform the desired procedure. Once the idea of possible departure is removed, the use of twitches, lip chains/ropes, war bridles, sidelines, elbow straps, or perhaps even laying the animal down may be used to assist in the performance of medical procedures. It is important to consider the use of pharmacological restraint when needed.
When applying any type of physical restraint to donkeys, it is imperative to start with the lightest application one expects to be effective and slowly increase the pressure or force as needed. This is similar to the current philosophy of equine training techniques using as little force as possible while handling the horse. It is also critical to let the animal become accustomed to the tools of restraint before continuing with desired procedures in order to initiate successful restraint training. One must also recognize that an uncomfortable donkey will seek comfort, but it appears that a donkey exposed to stimuli that produces pain can tune out the pain and most everything else about their surroundings. The donkey then may become oblivious to you and your restraint and will unlikely be tolerant or cooperative during the procedure.
The use of a twitch of any kind is often considered ineffective or to have limited effectiveness in donkeys and mules. However, this is not accurate. The twitch is very useful in these animals. The key to using a twitch is that one must use some other means of restraint to keep the animal in the working area. The twitch is then used to distract the donkey from responding to the specific procedure being applied such as passing a stomach tube, taking a blood sample, giving injections, or examining sensitive areas.
The authors’ preference for the use of a twitch on donkeys is the humane twitch (Fig. 2a and Fig. 2b). This type of twitch is applied in the demonstrated manner compressing the lips from each side rather than producing a twisting and snare grip created with the chain or rope loop on a single handle. Since donkeys often have much smaller and even perhaps more muscular upper lips, it is more difficult to keep the chain or rope twitch on the animal and control the pressure.
These types of twitches also cause more of an obstruction to the nasal opening than does the demonstrated humane twitch.
Figure 2a. The preferred humane twitch.
Figure 2b. Our preferred position of the humane twitch.
Another procedure found helpful in working with donkeys is taking away the use of one leg. This may be used on a foreleg by the use of an elbow strap or rope holding the leg up as means of keeping the animal still. When using an elbow strap (Fig. 3a and Fig. 3b) it may be made out of a two-leg hobble strap that has two rings and a buckle. The strap hobble can be placed around one pastern and the end of the strap is placed through the closest ring but not the second ring. Pull the leg up so that the forearm and cannon are in close proximity. Buckle the strap around the forearm for an easily placed elbow strap and allow the animal at least 10 minutes to adjust to the restraint. In order to use the rope method, use a soft rope with a loop tied at one end. Place a loop of rope around the fetlock, thread the free end through the loop and drop the free end of the rope over the back. Catch the rope underneath the animal, pick up the foot in the horizontal position and tie the rope with a quick release knot or tie it around the foot (Fig. 4).
Figure 3a. A strap hobble that can be utilized effectively as an elbow strap.
Figure 3b. A strap hobble positioned as an elbow strap to take away the use of a foreleg.
Figure 4. One method of taking away a foreleg for the purpose of either examining the lifted foot or as a means of restraint of the donkey for other examination or therapeutic procedures.
Rear legs may be taken up by the use of a sideline, or similar type system or placing a loop or strap around the rear pastern and pulling the foot up and backward. In order to keep a rear leg in place it may be necessary to tie a loop a around the neck to start the restraint process. This loop should be tied so that increased pressure on the rope does cause the loop to decrease in size and can easily be untied if necessary. It is the opinion of the authors that a bowline knot serves very well as the knot of choice in this restraint procedure (Fig. 5). Directions for tying a bowline knot can be found in most knot tying handbooks.
Figure 5. Completed bowline knot in correct position around the neck. This loop is the anchor point for several restraint techniques.
If you choose to restrain the donkey by means of a sideline, first tie a bowline as described above around the neck and lay the remaining part of the rope on the ground, holding the free end of the rope. Push the donkey over until the rope is in between his hind legs and slowly pull the rope up so that the donkey is aware and may become accustomed to the rope. Walk back up towards the shoulder and place the rope through the bowline and drop the rope around the rear fetlock that is on the same side as the bowline knot. Pull the rear leg up and tie the rope with a quick release knot to the loop around the neck (Fig. 6). There is a variation to this method to prevent the animal from kicking laterally and forward by tying the leg opposite of the side with the bowline knot. To perform this method of restraint, tie the bowline and lay the rest of the rope on the ground still holding onto the end. Push the donkey so that both hind legs are over the rope and walk back towards the shoulder with the bowline knot. If the bowline knot is tied on the left side, then pull the animal so that only the left leg is back over the line. Pull on the rope so that it raises the right rear leg and tie to the loop around the neck with a quick release knot.
Figure 6. An example of a commonly used sideline for the restraint of donkeys. Although it can be used for examination and treatment of the restrained foot other techniques may be better.
There is another position of restraint to tie the rear leg up beside a wall or fence to allow for better visualization of the bottom of the hoof. This technique is preferred if one is examining or treating that specific foot. It is not generally used for distraction or immobilization for other areas. It should be noted, that the animal is tied to a stout wall or fence, the hind foot is anchored to the wall or fence as it is elevated by a loop of rope around the fetlock and either tied with a quick release knot or held stable by an assistant (Fig. 7). Under no circumstances should the rear foot next to the wall or fence be the foot that is elevated. Such a maneuver can cause serious stifle and/or hip damage.
Figure 7. An example of the lifting and restraint the hind foot of a donkey for the purpose of examining or treating the lifted foot.
One other very useful restraint appliance is the war bridle (Fig. 8). Again, there are several types and configurations. The one we use most is simply a loop placed behind the poll and it comes through the mouth or underneath the upper lip (Fig. 9). It seems to work best when made with 1/4 - 3/8 cord. Slow tightening of the loop provides increasing pressure across the poll and on the selected part of the oral structures. The effects of the war bridle are very similar to the twitch. The best feature is that it allows for release and reapplication with the most ease and precision by the handler.
Figure 8. Small diameter rope loop that can be used effectively as a war bridle.
Figure 9. Suggested positioning of the rope war bridle on the donkey. Note the rope passes through the mouth and the end of the loop is at the base of the ear.
When choosing restraint method, remember that safety of the handler and the animal is the most important consideration in determining which technique you will use. The methods described above have proven useful in successful restraint of donkeys during examination and various other procedures requiring immobility of the animal. Listed below are several references that will further assist your knowledge of training and restraint [4,6].
Observations Regarding the Musculoskeletal System
As people have tried to redevelop or increase the number of American Mammoths during the last two to four decades, sound breeding practices have not always been utilized. Selection of breeding stock based on size alone has been the common practice. Additionally, rapid early growth has also been a trait sought after in the breeding stock. Use of these criteria with almost no regard for other desirable structural traits can be paramount to disaster. Whether it is from such selective breeding or genetic tendency within the breed such conditions as osteochondritis desiccans (OCD), cervical vertebral instability, flexural deformities, physitis, and angular limb deformities (Fig. 10 and Fig. 11) are among the conditions that appear to be more common in Jackstock than in horses. This is especially true for the larger size of Jackstock. Regrettably, not all breeders today are well versed in livestock production and some infrequently seek professional guidance which can result in a continuation of the production of animals with these conditions or the predisposition for these conditions. It is acknowledged that we may not have a complete understanding of the genetics of these conditions and how management techniques contribute to these problems.
Figure 10. Front view of a young donkey with carpal valgus.
Figure 11. Flexural deformity of the metacarpal phalangeal joint of a young donkey.
Clinical evaluation of breeding herds of Jackstock reveals at least subtle signs of these diseases even when blatantly obvious signs are missing. Abnormalities in gait and distension of joints with synovial fluid are common. It is suspected that many Mammoth donkeys never reach maturity as a result of complications resulting from such conditions. Unfortunately, many animals, euthanatized or that die from unknown causes, usually do not undergo necropsy.
Evaluation of available necropsy reports substantiates the following premises. Necropsy examination was performed on a number of animals that were 58” in height and above that died or were euthanatized for reasons of disease. Most of these cases revealed multiple lesions of OCD. Some of these lesions would have likely been identified in the live animal, but some were probably not clinically apparent. Lesions were in approximately the same locations as found in the horse. Lesions were found in two animals with dislocated coxo-femoral joints. Only one side was dislocated but both sides had OCD lesions. Clinical impressions are that coxo-femoral luxation is more common in the mammoth donkey that other size donkeys and horses.
Necropsy evaluation of a limited number of older jacks (7 - 18 yrs) suggests that degenerative change of the vertebral column is common. Many of the affected animals demonstrate increased ataxia with age. It appears that during the past ten years breeders have been more selective in their breeding stock. This perception, however, could be erroneous and the increasing quality of the animals today may be economically imposed.
In general, the largest of the American Mammoth Jacks were used to produce large draft mules. We are currently seeing a reduced interest in the bigger draft mules. As the recreational interest in mules continues to grow it is more in the area of saddle mules. The saddle mule producer usually prefers a smaller jack than does the draft mule producer. Today’s recreational donkey owner also often prefers a smaller animal and those recreational donkey owners who want the bigger donkeys require a donkey with greater visual appeal, greater athletic ability, and more correct conformation. Economics in short, the need to produce a highly marketable animal, may therefore be a factor in this breed improvement and the changing characteristics of the breed.
Veterinarians see essentially the same disease conditions in donkeys as they see in horses. The lameness related to speed events such as racing and highly skilled events such as cutting and reining are not very common. Such injuries are becoming more common in mules as they become increasingly expected to do those types of activities. Should the expectations of donkey performance continue, no doubt we will begin to see these problems in the donkey in addition to the mule.
To date we have not identified treatment regimens for these conditions in donkeys that vary significantly from those regimens used to treat the horse. However, the techniques used to reach a definitive diagnosis in the donkey may vary significantly from that used in the horse. For instance, a simple lameness examination can be quite difficult to accurately and effectively complete if one does not understand and make adjustments for the following differences of donkeys compared to the horse. First, the donkey’s increased tolerance for pain often inhibits the donkey from demonstrating gait abnormalities comparable to those exhibited by a horse with a similar lesion. Slight to moderate lameness is often not observed by the owners. A donkey that will trot on the lead to allow for good visual inspection is more likely the exception rather than the rule. Even walking in a progressive, relaxed manner may be difficult to achieve or accomplish in a strange environment.
After identifying the affected limb or limbs the "donkey factor" is still present. Donkeys not accustomed to being handled often show suggestions of pain in response to palpation and manipulation of their limbs. Those that are accustomed to such procedures may be more tolerant of modest discomfort than would a horse. In the authors’ experience the use of a hoof tester to evaluate the donkey foot for pain has proven unreliable. It works on some, but on many occasions it has failed to identify a rather severely affected foot or feet. Even sole abscesses may be missed with the use of a hoof tester in donkeys because of their tolerance of pain.
On many occasions, diagnostic local anesthesia is required to localize a site of pain. Even this method does not seem to be as effective as it is in the horse. If there is a marked improvement in lameness following a nerve block, it can usually be considered diagnostic, but this is not always the case. It is not known if there are slight differences in the innervation to certain areas of the limbs in the donkey or if this decreased response is due to other causes. This is not to imply that all donkeys have this degree of pain tolerance. There are those that demonstrate clinical signs very similar to those seen in the horse.
One of the greatest errors we can make is failing to recognize just how effectively the donkey can utilize this pain tolerance and also how effectively they can use other limbs and actions to compensate for pain associated with the locomotor system. It is normal for donkeys to spend more time lying down than a horse. Often if they have increased down time, the owner does not notice it. Often the clinical signs we see in donkeys are not a result of the primary condition. It may be necessary to work backwards from many clinical diagnoses to identify the primary lesion.
To illustrate this point consider a scenario that is frequently observed or relayed by attending veterinarians. The patient is a mature to geriatric donkey kept on pasture. With seasonal changes, the forages are lush, tempting the donkey to graze relentlessly. The donkey develops mild laminitis or has an exacerbation of an already existing condition. The donkey moves around a bit less and spends a little more time lying down. When standing, it compensates for the sore front feet by shifting more weight to the rear. No one really notices this subtle lameness. With time, the donkey develops laminitis in the rear feet as well due to increased weight bearing. The animal has laminitis in all four feet now. The donkey stands fairly even and walks a bit slower, appears stiff, and spends more time lying down. Since this has developed over days to weeks, the owner begins to note some changes, but nothing mandating attention. Soon the donkey develops some separation of the laminae of the left rear foot. Being very pain tolerant, the donkey puts more weight on the right rear foot. This increased load causes a more severe separation of the laminae of the right rear with associated infection that breaks out at the coronary band. The donkey shows overall muscle stiffness and soreness and is reluctant to put weight on the right rear and stands on the left rear foot. It is easy to make a diagnosis of an abscess of the right rear foot and treat accordingly. Needless to say, the results will be unsatisfactory.
Unless the veterinarian is aware of this tendency for progression of compensation, they will often not explore or evaluate the other extremities to a sufficient extent to make a complete diagnosis and instigate appropriate therapy. In reality, the veterinarian may be called to examine the donkey at any stage of this scenario. The signs demonstrated would vary based on progression of the disease. The primary diagnosis or cause of the problem is still the same despite the phase of progression. Granted, this may be an extreme example, but it occurs to this extent very often in donkey practice. It is also recognized that horses also will compensate for lameness and create life-threatening problem with the contralateral leg. In horses, clinical signs are usually sufficiently apparent to mandate veterinary examination much earlier in the process.
An additional point that needs to be presented is that laminitis is very common in donkeys. It does not always cause clinical signs that are sufficient to identify its presence and it will commonly elude hoof testers and radiographic evaluation. Rotation and/or sinking of the distal phalanx is far less common than in the horse. Mild to moderate periosteal reactions on the distal phalanx as a result of laminitis are common in many Mammoth donkeys that have never been lame. Laminitis of all four feet and of only the rear feet is much more common in donkeys than in horses. Laminitis should be high on the list of differential diagnoses of any donkey demonstrating lameness or reluctance to move around as well as those showing increased time spent laying down.
In addition to laminitis, sole abscesses and pedal osteitis are common. Perhaps due to a greater pastern angle, ringbone is often identified.
In contrast to their smaller relatives, the burros and standard donkeys, Mammoth Jackstock do not have what one would consider ideal hoof quality. The feet show lots of variation in size and shape (Fig. 12). The horn quality frequently seems poor; flaking, cracking, and breaking are common occurrences as is white line separations. This is in spite of, or maybe even due to, the fact that the walls of the Mammoth donkey hoof are much thicker than the walls of the horse hoof.
Figure 12. Lateral view of the front foot of a Mammoth Jack. Observe the irregular shape at the quarter somewhat suggestive of the evolution of the donkey foot from three toes to one toe.
Frequent changes in moisture content of the soil seem to be very detrimental to donkey feet. Lesion of the feet are very common in animals on pasture where the soil frequently changes from wet to dry and back again. Most American Mammoths will require shoes if they are being ridden or driven regularly. Since the hoof walls are thicker and in some individuals have more variation in shape than those of the horse, commercially available preformed shoes will not fit. The shoes have to be hand forged out of wide webbed barstock to punch the holes in the proper place for nail placement or the farrier must use normal webbed shoes and place the nails through the hoof wall outside the white line (Fig. 13). This latter technique appears to be satisfactory and certainly less expensive.
Figure 13. Ventral view of a Mammoth foot with a commercial shoe placed for nails to enter the white line. Note the amount of wall that extends beyond the shoe.
Fig. 14 demonstrates another unique problem seen in Mammoth Jackstock. This lesion initially looks like the site where gravel (hoof abscess) has opened and drained. This can appear with no history of lameness. The lesion does not heal as one would expect an abscess to heal, and in many cases it will proliferate moderately. Over time, it enlarges maintaining some degree of discharge and produces an enlargement at the coronary band. Actual coronary band enlargement varies. Both the skin above the coronary band and the hoof horn below the coronary band thickens. The cause of this is unknown. In a limited number of cases surgical excision has been beneficial, but the area has not returned to normal (Fig. 15). The proliferation and drainage has stopped. Keeping the foot trimmed short to minimize the flexion at that area seems necessary. In most cases this conditions does cause some abnormality of gait.
Figure 14. Dorsal view of the foot of a mature donkey several weeks after surgical excision of a proliferating coronary band lesion. Note the residual thickening of the skin and the hoof wall.
Figure 15. Dorsolateral view of a Mammoth donkey foot demonstrating an exudative proliferating coronary band lesion.
Marked dorsal shifting of parts of the coronary band as shown in Fig. 16 are also common. Again the cause is unknown but one wonders about the uneven application of concussive forces as the animal walks about on an unbalanced foot. There may or may not be development of a bulge around the coronary band resulting in a ridge in the hoof wall. Lameness is not usual. These seem to respond to regular careful trimming to balance the foot and increased exercise.
Figure 16. Dorsal view of the forefeet of a mature donkey with dorsal shifting of the coronary band.
Jack Sores
There is a condition seen almost exclusively in Mammoth Jackstock, more in males than females, known as jack sores. They are most often located on the flexor surface of the hocks. Sometimes they are on the flexor surface of the carpus and sometimes on the metacarpal or metatarsal region. They are seldom seen on the body above the elbow on the foreleg or stifle of the hind leg.
Most contemporary references to these sores attribute them to being Habronemiasis or summer sores that resulted from larval invasion of a skin wound. This being facilitated by poor hygiene, inadequate stable management, and unsanitary housing conditions. It is reasonable to assume that flies and in this case Habronema larva may become a factor in any wound. It is not presently the opinion of the authors that Habronema species are the cause of these lesions. If this genus of fly was the culprit it would be reasonable to expect the condition to be more widespread across the body and affect all donkey sizes. At the very least, they should respond to commonly effective habronemiasis treatments. Histological evaluations of tissues taken from the wounds are not consistently positive for the Habronema species.
Jackstock breeders of years ago attributed these sores to the fact that jacks are sluggish animals who often don’t get enough exercise and in many cases are stalled most of the time. They could not get much exercise even if so inclined. The feeding of a high carbohydrate ration, generally corn, was also considered to be part of the cause. Increased exercise and a reduction in grain was part of treatment and considered to be beneficial. A research project conducted on Jackstock during the middle of the 20th century reported minimal problems with jack sores as they all responded to reduced grain ration. Current Jackstock breeders have also observed this. We believe that there must be some connection.
What do we actually know about jack sores? They seem to occur most often as hot weather approaches and seem to have a sudden onset. It seems that they can appear almost overnight. Many develop on skin with no known previous injury. The lesions seem to initially start as a small fluid filled swelling in the skin and rapidly ulcerate (Fig. 17).
Cases observed during early development released a thick grayish foul-smelling fluid at the ulceration. Ulcerations do not appear to penetrate all layers of the skin. Following the initial ulceration, the area around the sores has marked inflammatory reaction and the lesions may spread significantly, remaining ulcerative for a time or may become proliferative (Fig. 18a and Fig. 18b).
Figure 17. Jack sore on the flexor surface of the hock of approximately 48 hours duration.
Figure 18a. Close up of a jack sore on the flexor surface of the hock. Duration unknown. Note the extensive proliferation of granulation tissue and the surrounding local swelling.
Figure 18b. A distal view of Figure 18a.
Jack sores, like summer sores, do tend to regress or improve with cold weather. They also appear to be helped by the frequent administration of ivermectin. Some breeders state that by giving ivermectin about 4 - 6 weeks before hot weather begins prevents their stock from developing jack sores. As previously mentioned, Habronema have not been identified in all biopsy samples collected from jack sores. In fact, there are very few such biopsy reports available. Most likely the Habronema species are part of the problem, but they could be a causative agent or a complicating agent of a sore already developing. It equally appears that there are nutritional components to the mystery of the origin of jack sores as well.
Currently there are no highly effective treatments for jack sores. If uncontrolled the proliferating sores can reach sizes sufficient to be considered life threatening to the animal. No doubt they have been treated with most available wound remedies and these treatments have been coupled with improved hygiene and nutritional adjustments.
Upon necropsy, it has been observed that these wounds, at least until they become extremely large, do not involve the structures underneath the skin. Some Jackstock breeders elect to surgically excise the affected tissues and treat the open wounds under bandages. The results reported have been good, but it is expected that post incision care of the resulting wound could require a great length of time. This therapy would be best if used on the smaller sores, as one would have concerns about extensively denuding the flexor surfaces of the hock.
Other sores have been successfully managed by administering ivermectin every 4 - 6 weeks. The animal is placed on a low carbohydrate ration or a no grain ration and the wounds should be treated with a topical medication. All types of topicals have been used to treat these sores. The authors prefer an oil based wound treatment containing an insecticide. Surgical excision or surgical debulking is probably necessary on those sores that are rapidly proliferating. Laser removal has not been used, but may be a reasonable therapy to try on such wounds. Steps are taken to see that the animal is allowed adequate exercise and is restricted from grazing on tall pasture when there is moisture on the forage.
In summary, we have very rudimentary understanding of the cause and very limited ideas for the proper therapy for this problem. Jack sores will undoubtedly remain a controversial subject among veterinarians and owners for some time.
Colic in Donkeys
If we choose to accept the common definition for equine colic, non-specific abdominal pain, we must assume that it does occur in donkeys. Although "colic" is anecdotally reported to be much less common in donkeys than horses. In reality we should temper this statement with some understanding of the difference between horses and donkeys.
It is generally accepted that donkeys have a much higher pain tolerance than do horses. In practice, probably less than 5% of the colic cases treated in horses are due to serious or life threatening conditions. Most patients respond well to a single treatment of analgesics, sedatives, oral laxatives, or some combination of the preceding. Some of these horses show rather severe signs of pain. If we accept that donkeys have a better tolerance for pain we must ask ourselves if donkeys do not have as many cases of colic as horses do or are they just not demonstrating clinical signs that would lead to their presentation for treatment? If the conditions are self-limiting, then we may never know that the donkey ever had colic. Today in the United States, where donkeys are remarkably more likely to be pets and recreational animals than work-stock, it is probable that necropsy examination is far less likely than it would be for a horse. In fact, we probably have little idea how the incidence of colic in the two species would compare.
Donkeys are considered to be prone to impaction colic. Considering their tendency to browse on some of the lesser digestible forages and their ability to conserve water, this seems to be a valid expectation. However, almost all the severe colic lesions reported in horses have been identified in donkeys. The conditions observed include: colon torsion, 360° volvulus of the small intestine, strangulating lesions of portions of the small intestine, colon displacements, uterine torsion, and the cecum wrapping around the colon.
Even when suffering from one of these severe intestinal disorders, donkeys infrequently demonstrate the clinical signs of pain as those demonstrated by horses. Such signs as profuse sweating, pawing, lying down, and rolling are usually not encountered when presented with a donkey with colic. Only a small portion of those with strangulation lesions of the intestine will even lie down as a result of the pain. Common signs of severe colic in donkeys include: change in attitude, walking away from their food, modest elevation in pulse, and occasionally lying down. Depending on the duration of discomfort, they may have changes in the mucous membranes and a weakened pulse.
Due to their increased tolerance for pain it is often very difficult to examine a donkey suspected to have colic and absolutely confirm the diagnosis. In actuality, it is often difficult to examine a donkey and determine which body system is the primary problem with confidence. Nothing seems to be more useful than the observations of a very astute owner or herdsman. Rectal examination when possible can often be a valuable asset to your diagnosis. In many cases of evaluating sick donkeys, however, the examination for digestive disorders and the treatment for routine colic may be a valuable part of the evaluation process.
In many cases a careful and detailed physical examination, coupled with the history and treatment for impaction type colic results in improvement in the patient even if a specific diagnosis is never apparent. This treatment usually consists of injectable analgesics and administration of oral laxatives (mineral oil) if there is no indication of fluid accumulation in the stomach. It is not uncommon for the transit time in such animals to be 48 - 96 hours. Depending upon the patient’s metabolic state, other supportive measures such as oral or intravenous fluids may be required. Like most conditions with donkeys, when you begin to see the clinical signs you are well behind the time for the best response to therapy.
Surgery
The scope of this text is not to duplicate materials already available to the veterinarian, but to share special differences between donkeys and horses. With few exceptions the surgical procedures performed on donkeys are the same as those on the horse. The veterinarian is referred to those already existing equine surgical texts for procedural details. Only known special considerations will be addressed.
Special considerations for anesthesia of donkeys are discussed in another part of this book.. Anatomical differences between donkeys and horses are also discussed in the Anatomical Differences between the Horse and the Donkey chapter of this text. Most identified surgical variations are due to these anatomical differences. A good example of which is the need to transect the connection between the superficial and deep flexor tendons when doing an inferior check ligament surgery for flexure deformity.
It is a frequently observed fact that post-castration hemorrhage is more common in the male donkey than the male horse. For this reason most experienced surgeons will ligate the spermatic cords of donkeys in addition to using an emasculator. Although it may apply equally to horses, delaying castration of the male until after the age of 3 months for mules and donkeys seems to reduce the incidence of post-castration evisceration unless the wound is to be closed via suture.
The smaller the size and lower body weight coupled with their mild demeanor, makes donkeys good candidates for surgical treatments. They seem to tolerate many post-operative appliances better than horses. Slings, casts, external fixation devices, and other surgical appliances are much more tolerated by the donkey in comparison to the horse.
Donkeys tend to bond to their environment, other animals, companions or owners/caretakers as quickly and strongly as any of our domestic animals. This bond can make post surgical management of donkey patients difficult. They often tend to not eat or drink and exhibit a depressed demeanor due to being out of their normal surroundings. It is not unusual to get a real favorable response by bringing in a pasture mate or in several cases donkeys have been discharged within 24 - 72 hours of major surgery just to get them back on feed and water. Many times overall success has been achieved by making major compromises in the anticipated post surgical management to return the animal to their usual environment.
These same reactions are also often noted in the animal being transported long distances or going to a multi-day exhibition. Since it appears normal donkeys can dehydrate themselves to a loss of approximately 30% of their body weight with no ill effects we are unable to fully understand what effects a post surgical response might create. Without a doubt it would affect drug dosages and drug metabolism.
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1. American Donkey and Mule Society, www.geocities.com/lovelongears
2. American Mammoth Jackstock Registry, www.amjr.us
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Affiliation of the authors at the time of publication
1Department of Large Animal Medicine and Surgery, 2College of Veterinary Medicine, Texas A&M University, College Station, TX, USA.
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