From foalhood to 4 years is when young horses develop the foundations for future health and soundness. Jane Nixon MRCVS explores the physical issues during these crucial early stages
Youngsters tend to be green and gangly, with their bodies developing in fits and starts. But early identification of any developmental abnormalities among these more usual growth spurts is important, as many such problems predispose sub-optimal performance in adulthood.
The aim for producers is to breed an adult horse who is as symmetrical as possible. Monitoring the foal’s limbs should begin at birth, as this is the time when problems may be identified and stand the biggest chance of correction.
Some elite sport horse producers ensure their foals undergo a physiotherapeutic examination at birth to reduce the effects of any laterality (one-sidedness) or torsion (twisting) that may have occurred during the birthing process.
Bumps and bones
Developmental limb deformities can show at varying ages and should be constantly monitored and corrected by way of foot balance, nutrition and controlled exercise. Signs of incorrect development include any dissimilarity between left and right limb angles, or other variations from the norm.
It is usual for the foetal bone cartilage growth plates to become progressively ossified. The limbs finish their lengthwise growth when all these plates have closed, usually by 3 years of age.
Bumps can occur due to inflammation of the growth plates, a condition called epiphysitis. The bumps tend to form just above the fetlocks or on the knees, appearing between the ages of 4 weeks and 18 months. They may self-correct over 4 to 6 weeks, but the main causes are excess weight and too much turnout on hard ground.
Careful management is required until the affected growth plates have closed.
While the neck and back are susceptible to similar problems, the signs are not so readily recognised. They may present as obscure lameness or loss of full control of movement (ataxia).
The interlocking skull bones may also show excessive bone formation, which can appear as bulges in facial and nasal areas. These are usually self-limiting and resolve themselves without treatment.
Conformation problems
As the youngster matures from foalhood and into the early stages of work, further problems can occur. These include:
➤ Bone outgrowing muscles, tendons and ligaments, with resultant twisting of the cartilage of the growth plates.
➤ Too great a weight gain, too early, with resultant excessive limb loading.
➤ Joint concussion caused by too much exercise on hard ground.
➤ An unprepared musculoskeletal system unable to cope with too demanding exercise.
Corrections are sometimes possible, provided the affected growth cartilage is still “open” and not fully developed. These are made by addressing possible causes and altering ground reaction torque forces by experienced farriery.
Attempts at such farriery techniques on closed growth plates are impossible, however, and may be counter-productive due to the resulting artificial pressures on other still “open” areas and on related joints.
The main cause of many problems is poor conformation. Culprits include foot asymmetry (fore or hind), toe-out conformation of the fore feet and straight or sickle hocks.
Attention to hindlimb development is of paramount importance. The hindlimbs are attached to the pelvis and spine at the hips and the sacroiliac joint, and consequently any weakness will affect the development of back, core and neck musculature.
Incorrect muscle development can result in reduction of balanced performance in the adult horse. Unmanaged limb abnormalities will lead to osteoarthritis and consequently faults in action and lameness, due to restricted stride pattern as athletic requirement increases.
Such deformities can result in subclinical lameness by 8 years old and overt lameness by 10 years, requiring ongoing management.
The producer must decide at an early stage whether the animal is destined for the athleticism required by the sport horse industry or will solely be aimed at the showring, where youngsters frequently carry too much weight and are less likely to enjoy a subsequent athletic career.
Feeding for healthy growth
Nutrition management plays an important role in young horse development. Diet is also linked with increasingly well-recognised hormonal influences.
By 12-15 months old, the typical yearling should have achieved 90% of his mature height, 95% of his bone length and 75% of his adult weight.
As the youngster matures, a balanced diet remains an essential part of helping him to develop into a strong, healthy adult.
All but extremely experienced producers are strongly recommended to take nutritional advice from feed manufacturers, who have trained nutritionists at hand.
Laboratory testing for EMS (equine metabolic syndrome) and laminitis is now the norm, particularly in broodmares for the avoidance of laminitis and the consequent reduction of predisposition in offspring and subsequent generations.
Similarly, it is known that hormonal influences in fast-developing 2-year-old colts may predispose them to orthopaedic problems, including laminitis and/or limb overload in the older horse.
Producing a young horse to the point of his first outing under saddle as a 4-year-old — and for a successful adulthood — is a skilled task. It is important to remember that any painful incident at this stage may have a lifelong effect.
Every aspect of the young horse’s development should be monitored constantly and every unexplained change investigated.
Above all, under saddle a balanced, empathetic approach should be established and maintained to maximise the youngster’s potential.
How training affects tissue development
Different skeletal tissues develop at different times. Tendons, ligaments and possibly cartilage are most responsive to “loading” in the first year of life, while bone is more responsive during the yearling and 2-year-old period.
Research has shown that 2-year-old racehorses in light work are likely to have a longer, sounder working life than those not raced until later. For dressage horses, a small amount of balanced work under saddle as a 3- and4-year-old will encourage the correct adaptation of bone for future work requirements.
Once the skeleton has matured, at around 5 years of age, training should be directed at muscular, respiratory and cardiovascular fitness.
Young horse checklist
Manage your young horse with the following steps:
➤ VACCINATION: leading vet Dr Derek Knottenbelt has identified that the equine herpes virus can cause inflammation of the trigeminal nerve associated with headshaking. As such, both the in-foal mare and her offspring should be vaccinated against the herpes virus.
➤ NUTRITION: seek expert advice on the correct dietary requirements for these early years.
➤ TEETH: check there are no erupting milk teeth, tushes (canine teeth), wolf teeth or molar caps before you introduce the bridle. Ensure, too, that the lower jaw excursion (movement) is equal to the left and right — which is usually 1.5 incisors’ width each way. This will prevent asymmetrical loading and pain of the temporomandibular (jaw) joints, with ensuing imbalance under saddle.
➤ TACK: it’s crucial that the first saddle ever placed on the young horse’s back should fit. Otherwise, there’s the risk of local muscle spasm and development of scar tissue, which may never resolve, causing lifelong alteration of limb flight path.
➤ TRAINING: avoid movements that compromise development. Extended trot, for example, will overexert the undeveloped abdominal core muscles, causing back muscle soreness from which the youngster may never recover. Always do all exercises from both sides/on both reins.