From the Sales Ring to the Training Track: Feeding During the Transition

Most Thoroughbreds destined for the racetrack will endure a short but intense period of yearling prep before entering training as young as 18 months of age, with many racing in their two-year-old year. Feeding these young horses is a challenge because nutrients must be supplied to support both growth and exercise. Additionally, little research has been done to quantify the nutrient requirements of horses of this age, particularly during the transition period from untrained yearling to intensely exercised two-year-old.

Ideally, the yearling Thoroughbred should have been on a sound nutritional program from birth, giving it the best opportunity to develop a strong skeleton able to withstand the rigors of training. If purchased at a yearling sale, the animal will likely have been on a high plane of nutrition for several months, so it is important to taper off the energy intake if the yearling is going to be turned out for some time before pretraining. Yearlings fresh from the sales can be maintained on good-quality forage (1-1.5% of body weight), including adequate pasture, and a feed formulated for breeding and growing horses. If the yearling is an easy keeper, cutting back the grain and feeding a low-intake concentrated balancer is a sensible approach to keeping the horse in proper condition while still providing essential nutrition.

As yearlings leave the breeding farm environment and enter training, major changes occur in their skeletons. Many of these changes are due to alterations in housing and exercise, but nutrition may also play a role. A recent study by Kentucky Equine Research reported significant decreases in bone mineral density during the first two months of pretraining in rising two-year-olds. This was followed by an increase in bone density that continued through the duration of the study. The yearlings entered training (day 0) in late autumn on a farm where regular turnout paddocks were available. The horses were confined in stalls for approximately six hours per day. The training intensity at this time was low, consisting of 15-20 minutes per day trotting in a paddock. One month into the study (day 28), the horses were moved to a racetrack training center where little or no turnout was available. For the remainder of the study the horses were confined in stalls for approximately 23 hours per day. From days 28-84, the horses (now two-year-olds) were lightly exercised, and from day 84-112 training intensity increased. From this time period onwards, horses were kept at an intense level of training. These horses were consuming a commercial fortified feed and grass/grass hay throughout the study.

Bone mineral content (BMC) dropped from day 28 until day 84 when the horses were confined to stalls with only light exercise. By day 84, BMC was significantly lower than day 0. When training intensity increased in the spring, BMC increased to levels that were not different from pretraining. Osteocalcin is a protein produced by the osteoblasts in bone and is an accepted marker of bone formation. Plasma osteocalcin levels dropped slightly from day 0-84 when the horses were confined and in light training. Levels increased from day 84-112 when the horses began intense exercise, suggesting an increase in bone formation. The results showed how confinement and changes in exercise intensity can affect bone mineralization and point very clearly to the importance of some turnout for racehorses in training.

Feeding Programs for Two-Year-Olds

Once the yearling has entered the training environment, a real concern for trainers is how differently to feed rising two-year-olds compared with older horses in the stable. A typical feeding program for an adult horse in race training consists of good-quality forage (grass and/or lucerne {alfalfa} hay, chaff, pasture turnout if available), grain/commercial concentrate, and supplements if necessary.

Forage must be fed at a minimum of 1% body weight per day, or about 4-5 kg (9-11 lb) hay per day, but more should be offered. The energy and majority of the nutrients are provided by grain and/or a commercial grain concentrate. Commercial concentrate feeds are usually fully fortified to contain all the energy, protein, minerals, and vitamins the horse needs provided it is fed at the recommended amount (usually about 4-8 kg or 9-18 lb per day) and is fed alongside good-quality forage. Some commercial racing feeds are formulated so that you can add your own grain (oats/barley/maize {corn}) to top up the energy intake. Rising two-year-olds will require more protein, calcium, phosphorus, and trace minerals than mature horses because they are growing as well as working.

For example, let’s look at an adult Thoroughbred in race training and his rising two-year-old stablemate in moderate work. Both horses are fed 5 kg (11 lb) of high-quality grass/lucerne (alfalfa) mixed hay and a 13% protein commercial grain mix that supplies 13 MJ DE/kg. The adult racehorse would require 6 kg (13 lb) of grain per day to meet its energy requirement, while the two-year-old requires 5 kg (11 lb)/day.

Although the hay and grain are not excessively high in protein or minerals, the adult racehorse’s ration supplies more protein, lysine, calcium, and phosphorus than needed because of the high level of intake required to meet the racehorse’s energy requirement. A ration using the same hay and grain mix also meets the nutrient requirements of the two-year-old in moderate work. Again, a fairly high level of intake provides adequate nutrients from feedstuffs containing fairly low concentrations of protein and minerals.

The bottom line from this comparison is that most rations fed to adult racehorses contain adequate protein, calcium, and phosphorus for rising two-year-olds. If energy intake must be restricted in a rising two-year-old (if it is an easy keeper, for instance), higher levels of fortification may be needed. In these cases, topping up the diet with a ration balancer would be appropriate.

In conclusion, the nutrient requirements of the rising two-year-old fall between those of the growing weanling/yearling and the adult performance horse. If the rising two-year-old is in training, feeds that are typically formulated for adult performance horses are appropriate because the elevated level of feed intake required to meet the energy required for exercise will provide the extra protein and minerals needed for growth. In addition to correct nutrition, it is important to note that recent research supports some level of turnout time to maintain bone mineral density in young horses entering the training environment.