MEDICAL ARCHIVES
08.02.2006
The Short Lay Off - Bone and Fitness Changes
Most trainers agree that when a horse that has raced hard and ‘lost its edge', 'trained off’ or 'lost its willingness’, to put effort in its work, it's time to give it a rest or lay-off. The length of the 'lay-off’ is often relative to the horse's physical state, its general vitality and appetite, any underlying sickness (eg ' the virus'), injury or lameness and the time of the year or most importantly, the races it can be set for when it returns to work.
Whilst most trainers would like to give a well performed horse as long as possible, the plans and economics as dictated by the owner(s) often result in a bare minimum layoff or a short-term 'freshen up'.
Recent studies have investigated the relationship between the length of the rest period and the incidence of musculoskeletal injury; particularly bone injury and fracture, when a horse returns to full time training.
Studies by Dr Susan Stover and colleagues in California in the early 1990's reported on the increased incidence of what was termed 'catastrophic bone failure' in horses that were given a short layoff and then returned to full racing in a short, intensive preparation.
Dr Albert Kane and other workers in 1996 reported that the incidence of bone fracture was linked to the remodelling of highly calcified areas of bone that are laid down in 'stress' areas of high bone loading. During the first month of a rest period, the rate of remodelling is slow, but it appears that the shift of calcium from strengthened areas back to weaker areas or regions of the long bone that area not subjected to high loading in a galloping horse, speeds up to during the 4-8 week rest period.
The lower limb bones such as the cannon, pastern and pedal bones are not subjected to remodelling to the same degree as the shoulder, femur (long hip bone) and the pelvic bones. A fit horse may only lose 20% of its oxygen up take capacity over a 6-8 week rest period. Theoretically, such a horse only requires 2-3 weeks of intensive training to regain muscle fitness. However, on return to high loading exercise, the decalcified areas are subjected to high loading forces and risk of bone failure can be increased by over 300%. Catastrophic bone failure results in severe fractures and the need to destroy the horse.
Facts and Stats
- When rested due to an injury, a horse given 8-10 week's work will lose its 'oxygen uptake' fitness within 2-3 weeks and require a full training program to reach its pre-rest fitness.
- A horse that has been in training for 20-26 weeks will only lose 10% of its 'oxygen uptake' fitness per month when rested, requiring less work, requiring less work to regain its pre-rest fitness.
- A horse given 2-4 weeks rest does not lose appreciable bone strength, but a horse given from 4-8 weeks lay off remodels its major load carrying bones, significantly weakening the knee joint, hock, shoulder and major hind limb bones.
- Catastrophic bone failure can results in the virtual explosion of the under limb bones into multiple fractures of up to 40 pieces of bone.
Management
Although a lot more research has to be completed to provide the best guidelines on how to manage a horse on return from a short layoff of between 4-8 weeks, the following preliminary recommendations are worth adapting:
- Return the horse to training, giving a graded increase in speed, especially when galloping around comers on the track, over a 4-6 week period before reaching all out speed under race conditions.
- Provide a daily supplement of calcium, such as CALCIUM PLUS with added Vitamin D3, to help insure an optimum intake of calcium for recalcification and modelling to strengthen regions of bone that have decreased loading' capacity due to remodelling during the rest period.
- The longer the layoff, the longer the time required to recalcify and strengthen high stress areas of the leg and spinal bones
How Do Horses Respond to Training - New Findings
It is well known that the blood-vascular, respiratory and muscular-skeletal systems of a horse responds to a graded increase in fast work and weight loading during the initial few weeks of training.
Professor Reuben Rose and co-workers at Sydney 'University carried out a long term training study to monitor the increase in fitness, as measured by amount of oxygen absorbed into the blood and muscles available for metabolism. Prof. Rose trained two groups of horses on a high speed treadmill to reduce many of the influences of wind, track surface and a jockey's skill under race conditions. Professor Rose and his learn found that:
- A horse reaches 50% of its maximum fitness within the first 2 weeks of training, provided it is worked at speeds up to a medium trot over 1500 metres daily.
- A horse takes a further 10-12 weeks of slow conditioning work and fast out sprints in a graded, conventional training program to reach 70% of its maximum oxygen uptake {VO2 max) fitness capacity.
- Most horses are only 70% fit when first raced at 10-12 weeks into training using conventional training methods.
- A horse may take up to 5-6 months to reach its optimum level of fitness.
Facts and Stats
- Up to 80% of the energy required at the 'all-out’ gallop in a fit racehorse is metabolised using oxygen.
- A fit horse has a maximum oxygen uptake at full speed (velocity), termed VO2 max of 165 mL/kg bodyweight or roughly 82.5 litres of oxygen a 500kg racehorse, or the same rate of oxygen used a 2l 4-cylinder car travelling at 100 km per hour.