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Foals may be born with limb deviations or ‘bent’ legs due to an inherited risk, excess energy intake in the mare and poor mineral and trace-mineral nutrition in late pregnancy or Uterine Distortion Syndrome (UDS) in an overweight mare (refer to Handy Hint 2). Calcium and trace-mineral nutritional deficiencies may also delay normal bone and cartilage development in the unborn foal in late pregnancy.
An excessive growth rate during the first 4-6 months as the foal grows quickly and virtually becomes ‘too heavy’ for its legs to support its weight, can compress joint cartilage before it fully matures by 5 months of age. It is important to regularly
monitor a foal’s joints for signs of early joint disease, bone developmental problems and abnormalities in limb growth and acquired conformation problems, such as turned-out limbs or upright pasterns as a result of over-feeding or a poorly balanced or inadequate diet.
A rapid growth rate can be fueled by high milk intake by a young foal (up to 20 litres a day can be produced by a 500kg mare) during the peak of lactation (4-10 weeks
after foaling), resulting in the overloading of joints due to excessive bodyweight, with restricted or uncontrolled excessive exercise.
In more severe cases, devitalisation of joint cartilage and overloading of the subchondral bone (the layer of bone directly under the layer of joint cartilage) can occur due to excess bodyweight and the ‘shearing’ forces on the less resilient
cartilage. This can result in cartilage death and lifting of the cartilage off the underlying subchondral base on the bone cap within a joint as it is loaded. When combined with subchondral bone collapse due to poor calcification, poor cartilage quality and reduced weight bearing capacity, as well as decreased blood supply as a result of excessive loading or trauma from exercise, the lifting of the devitalised
cartilage and shearing off the underlying bone on the bone cap can result in
Osteochondritis dessicans or OCD.
Joint cartilage does not have a nerve or blood supply and relies on drawing in nutrients from the joint fluid as the cartilage compresses with loading and rebounds during each step or limb cycle. Young horses which are overweight also tend to not exercise adequately and ‘stand on’ and compress on their joint cartilage layers,
which increases the risk of OCD.
Early signs of Joint Pain in Young Foals
It is important to regularly observe young foals which are growing rapidly on high producing lactating mares for signs of developing joint disease, before the joints themselves become enlarged or the growth plate spreads (‘squashing’ due to excess weight bearing or exercise) or becomes reactive or inflamed, referred to as physitis (fetlocks) or epiphysitis (knees, shoulder joints, hocks and stifle joints).
You should observe all foals on a daily, or at least at 3-4 day intervals, for the early signs of developing joint disease, particularly ‘good doers’ which can become “too big, too early”
- More time spent lying down, especially after paddock exercise, as compared to other foals - this is often the earliest sign of discomfort due to joint cartilage inflammation and subchondral bone overload, with development of OCD or a devitalised cartilage flap as it detaches from the underlying subchondral bone in the front fetlock joints in particular.
- Minor joint fluid swelling in the front fetlocks, combined with stiffness and difficulty in keeping up with the mare or other foals in the paddock.
- Tendency to stand with the front limbs slightly bent forward at the knee (‘rocking at the knees’) when standing or just after exercise, with a straighter pastern and more upright conformation (often described as “contracted tendons”) in the front limbs, because of low grade joint pain resulting from a developing cartilage defect. There is a genetically influenced form of tendon contraction in Thoroughbred foals which is exhibited at birth, but may correct within the first 4 weeks of age.
- Attempts to lie down instead of standing still after activity, with bending forward at the knees and difficulty in lying down comfortably.
- Progressive development of upright conformation - straight pasterns, ‘up on the fetlocks’, as fetlock osteochondrosis and early OCD is frequently seen in young, rapidly growing foals up to 6 months of age.
Careful observation of young foals during the first month of age can also help to determine foals which are at risk of developing ‘wobbler syndrome’. This syndrome is considered to be due to the abnormal formation of cartilage in the cervical
5-6 junction in the neck vertebrae. It is most common in rapidly growing foals or possibly those with a genetic risk of developing the syndrome. It is considered to be a skeletal developmental problem (SDP) and related to Developmental Orthopaedic Disease (DOD).
The syndrome causes malformation of the cervical vertebral canal and cartilage discs at the cervical articulation, which can ‘pinch’ the spinal cord and result in nerve damage and partial paralysis and incoordination of hind limb movement. Although
it is often not manifested until 9-12 months of age, with up to a 2% incidence in Thoroughbred foals, the early signs in susceptible young foals between 2-6 weeks of age include:
- Inability to learn to trot - affected foals either walk, canter or pace.
- Standing with the front legs wide apart to balance the hindquarters, instead of standing with one front leg forward when feeding.
- Problems with coordination and balance when the body ispulled to one side by grasping the tail as a foal walks.
- Lack of coordination when attempting to feed from a ground feed bin - bumping into the bin with the nose before feeding.
If you observe any of these signs, it would be advisable to have the foal examined for neurological damage by your veterinarian.
Early cases can be managed to improve nerve function to prevent further cartilage and bone malformation by supplementing with additional trace-minerals and restrict
energy intake, but in most cases, the symptoms are progressive and the foal becomes severely incoordinated and incapacitated.
Management to Avoid Cartilage and Subchondral Bone Weakness
Joint cartilage does not have its own blood or nerve supply and relies on exercise to compress and rebound to draw in joint fluid to fuel its development and resilience. If a young horse develops joint pain, it signifies that the cartilage is diseased or poorly developed, or a dying OCD cartilage flap has lifted off the highly sensitive subchondral bone at the end of the bone shaft before the growth plate and is carrying excess loading or is worn away by over-exercise.
- It is essential that the diet contains adequate bone minerals for bone development (calcium, phosphorus and magnesium), trace-minerals, especially copper, zinc and manganese, as well as selenium and iodine, which are widely deficient in Australian soils and pastures (refer to map of soil deficiencies in Australia Page 4), as well as vitamins A, D, E and K.
- Feeding a well formulated pellet or mixed ration during the last 3 months of pregnancy, during lactation and after weaning will help to avoid joint cartilage defects when combined with adequate, but not forced or excessive paddock exercise. If the full recommended amount of a prepared mare and weanling feed is not being fed due to good spring pastures and risk of over energy supply and body weight gain, then a daily supplement of a product such as Kohnke’s Own Cell-Grow™ should be feed to make up shortfalls of these important nutrients.
- Aim for medium growth rates in a young foal to roughly double its birth weight by one month of age, (to 100kg for a foal of 50kg birth weight), double it again by 4 months of age (to 200kg body weight) and double it again by 16-18 months of age (maximum 400kg). Monitor growing foals every 7-10 days and if early signs of joint pain are present, confine the young foal to a yard with the mare to prevent it exercising excessively and traumatising the devitalised joint cartilage. Check the mare’s ration to ensure that it provides adequate nutrients for bone and cartilage development. You may wish to email [email]email@example.com[/email] for ration analysis using the FeedXL ration analysis program - this is a free service.