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Forage-only diets have positive effects on fluid balance

Forage-only diets have positive effects on fluid balance

This study examined the impact on body weight and plasma volume during a 12 hour fast in trotters in training when fed either a diet of energy rich haylage or a diet of 50:50 haylage:oats. The same haylage was used for the two diets and bots diets covered the maintenance requirements × 2 and were supplemented with minerals and salt.

The horses were about 3 kg heavier and drank about 3 L more water when they ate the forage diet than the 50:50 forage:oats diet and the faecal dry matter (DM) concentration was lower when they were fed only forage (20.9 vs. 25.2 %), e.g. the faeces contained more water. During the fast, the horses lost more weight when they were on the forage diet than the forage:oats diet and after 9 hours there was a significant difference in body weight between the diets (Figure 1). On average the horses lost 2.4 kg more during the fast on the forage diet, almost as much as they were heavier before the fast. That they lost more weight during the fast on the forage diet could be due to that they lost a larger amount of water via the faeces, since the faecal DM concentration was lower (e.g. the faeces was wetter) when they ate only forage. In this study the horses were standing in their boxes during the fast, but it is likely that a more rapid weight loss would have been observed if the horses for example were transported to a competition which implies nervousness and defecation. The horse being about 3 kg heavier during training at home is neither a disadvantage.

Text 8.1 figur 1 eng

Measuring the concentration of proteins in plasma (total plasma proteins TPP) is an indirect measurement of changes in the horse’s total plasma volume. The higher the concentration of TPP the smaller plasma volume. After 8 hours of fasting on the haylage:oats diet a significant increase in TPP was observed, which is a sign of beginning of dehydration (Figure 2). On the haylage only diet it was not until the last hour of fasting (hour 11-12) that an increase in TPP could be observed. This indicates that when horses eat only forage and no concentrate they can better maintain their fluid balance. Probably because on a high forage diet they have a larger fluid reservoir in the large intestine since the forage fibres bind water.

Text 8.1 figur 2 eng

In conclusion, a forage-only diet might be an advantage for the horse’s fluid balance and facilitate for the performing horse to maintain its fluid balance during the unintentional fast that can happen at competition days.

Sara Muhonen, AgrD

Reference:
Connysson M, Essén-Gustavsson B, Lindberg JE & Jansson A. 2010. Effects of feed deprivation on standardbred horses fed a forage-only diet and a 50:50 forage-oats diet. Equine Veterinary Journal (Suppl. 38), 335-340.

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