DEVELOPMENTAL JOINT DISEASE

Dr Nicholas Kannegieter BVSc, DipVetClinStud PhD FACVSc Specialist Consultant Equine Surgeon

The following notes are part the Equine Surgery component of the Distance Education Program for Veterinarians. This program, conducted by the University of Sydney Post-Graduate Foundation in Veterinary Science, has achieved international acclaim and is accessed by Equine veterinarians from around the globe. Dr Kannegieter, a Specialist Consultant Equine Surgeon, teaches the Equine surgery chapter. We wish to acknowledge the contribution of the University of Sydney Post-Graduate Foundation in Veterinary Science to the equine stud industry and are grateful for the contribution to the Stud Bulletin..

Developmental joint disease includes osteochondritis dissecans (OCD), bone cysts and angular limb deformities.

Osteochondritis Dissecans (OCD)

The most commonly recognised developmental joint disease is OCD. The appearance of clinical signs associated with OCD can sometimes be delayed many years, particularly if only mild lesions have occurred, and the horse has been allowed to mature before vigorous exercise has commenced. Cases appearing in older animals can often present as a degenerative arthritis, however the location and appearance of lesions is indicative of a long-standing OCD lesion. All breeds of horses may be affected, however the majority of cases have been recognised in racing breeds. It is important to remember that any particular surface may be affected, including vertebral articulations, with more than one joint frequently affected. For this reason any lameness in young horses, particularly if bilateral, should include OCD as a differential diagnosis. Clinical findings: The most prominent clinical sign in cases of OCD is effusion in at least one affected joint. Effusion may not always be evident in the contralateral joint, even though radiographic evidence of disease exists. Lameness is variable, but is usually only mild to moderate. The lameness may be difficult to completely abolish with intra-articular local anaesthesia. Muscle wasting is often evident in long standing cases of shoulder and stifle OCD.

Typical appearance of hock Stifle effusion typically seen in young with effusion due to horses with stifle OCD OCD fragments

Diagnosis: The age of the horse, its size, sex and the presence of joint effusion, should be factors suggesting a diagnosis of OCD. Confirmation is usually made by radiography. If clinical signs are only apparent in one limb, the contralateral joint should always be radiographed and the horse closely examined for abnormalities in other joints. A neurological examination may be indicated to determine if cervical vertebrae are affected.

Treatment: Conservative therapy consists of restricting exercise, slowing growth rate and ensuring that there are no dietary vitamin or mineral deficiencies or excesses. Excessive feeding of grain should be avoided. Conservative therapy is successful in approximately 20-30% of cases, but is dependent upon the site and severity of the lesion and how early in the course of the disease the lesion is detected. Up to 12 months convalescence may be required and joint effusion and lameness may be present for a considerable period of this time.

Drainage of the joint and intra-articular steroid injections are most likely contra-indicated. IA hyaluronic acid or long term IM PSGAGs may improve the prognosis in selected cases. However if severe effusion is present and there is radiographic evidence of fragmentation then surgery is the preferred option.

Surgical treatment is usually recommended when OCD fragmentation has developed. Arthroscopic surgery is the technique of choice. Approximately 70-80% of cases respond to arthroscopic surgery. Improvement in clinical signs is often evident within weeks of surgery. Post-operative care consists of four weeks of stall confinement, then four weeks of hand walking, followed by paddock rest for a further 8 to 16 weeks. This should be modified to suit individual cases. Some horses, primarily those with small intermediate ridge OCD or plantar fetlock lesions, can resume exercise within a week of surgery.

Arthroscopic appearance of fragment. This is a very typical size.

Intra-operative and radiographic photographs of lesions, taken during surgery by Dr Nick Kannegieter.

After graduating from the University of Sydney, Nick completed a PhD in Equine Surgery at Massey University in New Zealand, followed by a position as Surgical Registrar at the University of Sydney. He is a consultant Specialist Equine Surgeon to Veterinary practices throughout Australia, where he performs r e s p i r a t o r y , c o l i c , t r a u m a , uro-genital, arthroscopic, orthopaedic & general surgery.

Bone Cysts

Bone cysts occur most frequently in the stifle joint, but can occur in any joint, including the pastern and elbow joints and carpal bones. The cause of bone cysts is uncertain, but may be related to dietary abnormalities and have a similar pathogenesis to OCD. Trauma to the articular surface can result in cyst formation in some circumstances. The treatment of choice is surgical evacuation where access to the cyst is feasible. Conservative therapy may be successful in some cases, but many will suffer from long term degenerative joint disease. Recently corticosteroid injection has been suggested as a possible treatment op-tion. In my experience this has had little success, particularly for fully developed cysts. This is not surprising considering the presence and structure of the cystic contents which would seem to make treatment by medical or conservative means far less likely.

OCD of Stifle Typical stifle lesion seen on Following elevation of the arthroscopy lesion. Loose cartilage and damaged bone is removed at surgery

Typical bone cyst in stifle. Note the communication with the joint space, which is typical of bone cysts

Cyst in carpal (knee) bone. Note the increased density around cyst which is also typical of bone cysts

Bone cyst in proximal first phalanx of fetlock joint.

There are many conditions in young horses, which can mimic cysts. It is important to differentiate those that may be potentially normal or clinically insignificant from those which may result in lameness.

These cyst like structures in The pastern can also develop Blood vessel spaces joint the carpal (knee) bones are cyst like lesions. These are recesses, which can often commonly seen in young also more likely to be a result overly joint spaces, should horses. They seem to be more of immaturity rather than true not be confused with bone a result of immaturity and are cysts. cysts. rarely evident in adult horses.

Pre-operative radiograph demonstrating Intra-operative view of cyst. Note the stifle cyst. opening of the cyst (large arrow) is surrounded by damaged cartilage (example at smaller arrow)

Intra-operative view showing the cyst Intra-operative view of the cyst following being debrided debridement back to healthy bone.

MICRO-MANAGING GROWTH IN YOUNG HORSES – THE SYNCHRONICITY OF PASTURE, SOILS AND GROWTH PARAMETERS

Dr Jennifer H Stewart BSc BVSc AAIM Dip BEP PhD MRCVS

Equine Veterinarian and Consultant Nutritionist

A major influence on the creation of a sound, athletic sale yearling and future success at the track, is pasture availability throughout the rearing process. From the time man first began to confine horses into enclosed spaces some 20,000 ago at the end of the last Ice Age, pas-ture management became necessary. The ability of pasture to support reproductive function in mares and growth and development of young horses is dependent on optimum pasture and soil management. A balanced approach to soil and plant management can ensure sustain-ability and the best outcome in terms of equine health and productivity.

The pregnant mare: Ongoing studies in soil science and research into the impact of pas-ture on growth parameters of young thoroughbreds has resulted in management strategies that can be readily applied in most situations to optimise herbage growth, reduce feeding costs and produce a strong, sound yearling. Correct nutrition is essential for productivity - for the broodmare this is measured as ability to reproduce, year after year, the genetic po-tential of both her own and the sires bloodlines; for her foal it is measured as the ability to fulfill that genetic potential.

Most pasture species are deficient in one or more trace minerals and proteins and although milk quality and quantity largely determine post natal foal growth and development, for the first 2-3 months of life after birth the foal is totally dependent on it’s own mineral reserves, which must be built up during the last 3 months of fetal life. Recent research in New Zealand has found that if the pregnant mare does not receive adequate trace minerals it is not possible to make up for this after birth by supplementing the foal - the incidence of physitis and cartilage lesions in their foals is the same - whether or not the foals are fed a balanced feed after birth. So before we have the opportunity to feed the young, growing thoroughbred, we have the chance to guide its development while it is still in utero - by correctly feeding the mare.

For most of the 50-60 million-year evolution of the horse, stud nutrition has been based on pasture and mares milk. But to support optimum growth, the early maturing racehorse re-quires more nutrients than are available either from pasture or milk. Studies in Australia, New Zealand and the USA have shown that growth rate of foals is strongly influenced by month of birth. This is related to seasonal reductions in pasture availability, which limit milk production and restrict growth in the unsupplemented foal.

Attention to detail in nutritional management is critical in growing animals. Diet, feeding management and exercise are involved in various veterinary clinical syndromes and many musculo-skeletal abnormalities did not occur in horses prior to domestication. In a large se-ries of fossil material from around 20 million years ago, up to the time of domestication about 6000 years ago, the following lesions were not seen:

● OCD in any site, including wobblers ● Navicular disease ● Sesamoiditis ● Splints – except for one sample from Bolivia ● Spavin ● Chronic laminitis ● Arthrosis – except for one case which had arthrosis and osteophytes in the vertebrae.

NEW ZEALAND STUDIES ON PASTURE & FOAL GROWTH: A comprehensive study of studs at Matamata in the Waikato provides a valuable reminder of the importance of local and regional knowledge. From this survey of 120 foals on 13 farms came many Group 1 winners with highly successful track performance. Researchers measured the nutritive value and major element content of Waikato stud pas-tures in different seasons and found important correlations with various growth rate pa-rameters of young thoroughbreds. Several pasture and soil characteristics impacted significantly on growth variables: ● higher weight growth with higher winter pasture protein content; lower weight growth

with higher pasture magnesium in spring and summer; ● increased cannon bone growth with concentrates high in phosphorus, calcium and

zinc ● increased height growth with higher pasture sodium and decreased height growth with

higher soil potassium levels; ● decreased girth growth with high potassium pastures and higher mare and weanling

stocking rates. SEASONAL GROWTH CHANGES: The studies concluded that the strong correlation between winter pasture crude protein and foal growth warranted protein supplementation. In addition, pastures barely met minimum phosphorus requirements of growing thor-oughbreds from weaning in April through till the January sales. Feeding oats did not cor-rect for the phosphorus deficiency and there was a strong positive correlation between weanling growth rate parameters and the phosphorus content of the concentrate used.

Herbage calcium levels in May and June correlated with cannon bone length – relative bone growth rate increased with higher levels of pasture calcium. Strong associations were found between magnesium intake in November and December and weight gain, length and girth measurements. The young thoroughbreds in the Waikato did not obtain sufficient sodium from pasture. This situation was more acute on properties with a history of potassium-bearing fertilizers as potassium displaces sodium in soil and plant systems. Higher levels of sodium intake in November and December were associated with higher girth measurements; in January and February with greater cannon bone growth rate and in May and June with greater whither height.

Higher potassium levels of pasture in each season were associated with lower growth rates and this was thought to be due to the negative relationship potassium has on other cations including magnesium and sodium. Herbage calcium peaked in autumn, whereas phospho-rus peaked in spring and autumn, widening the calcium:phosphorus ratio such that rapidly growing thoroughbreds required supplemental calcium and phosphorus over the winter period. These variations demonstrate the importance of diet analysis and regular pasture and soil monitoring.

SOIL BALANCE: Soil mineral balance has an impact on the % wastage of pasture, plant flavour and sugar content, control of plant nitrates and the quality of the pasture. Plant mineral deficiencies not only occur due to lack of a soil supply, but are also created by imbalances. An excess of any nutrient will always cause a deficiency in some other element. Where soils are deficient in cobalt, copper, molybdenum and selenium, mixing these minerals with fertiliser can increase pasture levels. Application rates should be calculated carefully as iodine, selenium and molybdenum can accumulate to toxic levels in certain plants. Excess soil molybdenum can accumulate in pasture and depress blood copper levels and high soil iron and sulphur can reduce copper absorption, cobalt uptake and induce vitamin B 12 deficiency.

Nutrient interactions are complex and require careful consideration when planning pasture and soil management programs. A balanced approach is achievable with the technological tools available to assist with soil and land management. These include a comprehensive chemical and biological soil audit, plant tissue analysis and in-field tools such as penetrometers, conductivity, pH and soil moisture meters. Such tests allow identification and fine-tuning of the role of soil balance and pasture nutrients on foal growth parameters.

Both the Waikato and other international studies have shown a highly significant influence of date of birth and significant differences between studs which are not accounted for by genetics. The influence of month of birth in the New Zealand studies is linked to the de-cline in pasture availability in November, which affected mare milk production and re-stricted growth in unsupplemented foals.

GROWTH PARAMETERS: These findings demonstrate the importance of monitoring foal growth parameters, pasture trace element status and soil characteristics for individual studs. Building a sound database will allow more efficient management and fine-tuning of pasture to ensure nutrient supply meets requirements during periods of peak demand in terms of trace mineral intake and pasture growth.

Routine recording of height and weight of young horses is by no means a recent concept and many studs in Australia, Kentucky and Ireland have years of records, which allow growth patterns of individual horses to be compared to the age band and bloodlines. Devia-tions from normal in foal growth curves can occur in many situations, including cases of over- and under-nutrition; insufficient or poor quality mare milk production; variations in pasture quality or quantity and the presence of subclinical disease.

Charting growth provides a reliable, objective measure of over- or under-performance and allows early intervention. Weight scales are necessary as weight tapes are inaccurate in young horses, due to changes in body shape and density and leg volume. The relationship between height and girth changes at 4 months – before 4 months height exceeds girth, but afterwards girth exceeds height.

Examination of growth curves from young horses that have developmental orthopaedic diseases often show periods of accelerated or erratic growth. Studies on weanlings that developed stifle OCD showed excessive weight gain in the 3rd and 5th months of life – coinciding with the greatest risk period for development of stifle OCD.