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Growth, training and health in yearlings fed a forage-only diet

Growth, training and health in yearlings fed a forage-only diet

A Swedish study has examined growth, exercise response and health in 16 Standardbred colts fed a forage-only diet. The forage was grass haylage with > 55% dry matter (DM), > 11.5 MJ metabolizable energy/kg DM and > 13% crude protein. The forage was complemented with 1 kg pelleted lucerne, 100 g molassed beet pulp and minerals.

The study lasted from August to December 2010 and the horses were between 400 and 518 days old at the start of the trial. The horses spent most of their daytime together outside in a large paddock with free access to forage. The training started in September with breaking, within 5 weeks all horses were adapted to a jog cart and trotted slowly (~ 3.7 m/s) for 3 km on an oval racetrack 4 days per week. During week 7-9 the horses trotted 5 km 4 days per week in the same slow pace. Week 10-17 they were still training 4 days/week but the speed was gradually increased to 5.6 m/s (3 min per km). About one-third of the training was performed at the oval racetrack and two-thirds on a slightly hilly track.

The horses body weight, body condition score, wither height and cannon bone circumference below carpus increased from August to December (Table 1). The results show that growth and also some fattening occurred. The horses in this study have on a forage-only diet had a slightly higher growth rate in comparison with other studies on growing horses. The authors therefore conclude that free access to a forage-only diet with high energy and nutrient content does not seem to limit the growth of horses in training. One reason for the high growth rate on the forage-only diet could be that the horses had free access.

The number of training days per month varied but the total distance trained increased from October to December. In December the horses could without problem trot 5-7 km at a speed of 5.6 m/s (3 min/km). The heart rate during training tended to be lower in December than in October and the heart rate 3 minutes after training was significantly lower in December than in October (Table 2). In December the horses also had almost as high levels of muscle glycogen (532 mmol/kg dry weight) as adult trotters in training.

The horses’ health status during the study was examined by an independent veterinarian. They were considered to be of good health and lost training days due to health problems were few (< 10%). Most of the health problems were injuries that happened during the time the horses spent in the paddock, which is not uncommon in year-old stallions that play and thereby accidentally injure themselves or each other.

In conclusion this study show that year-olds in training with free access to a forage-only diet consisting of high-energy forage grow well, have normal body condition and muscle glycogen content, reaches a conventional training goal and are in good health.

Sara Muhonen, AgrD

Ringmark S, Roepstoff L, Essén-Gustavsson B, Revold T, Lindholm A, Hedenström U, Rundgren M, Ögren G & Jansson A 2013 Growth, training response and health in Standardbred yearlings fed a forage-only diet. Animal 7, 746-753.

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