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The horse’s stomach – size, pH and gastrin

The horse’s stomach – size, pH and gastrin

In adult horses the stomach volume comprises about 10% of the gastrointestinal tract. Horses are large grass eating animals, herbivores, adapted to eating grass which takes long time to gather, chew and swallow and a large stomach for storing of food is therefore not necessary. The horse’s stomach should never be completely empty, the digesta stays here about 2-6 hours and the stomach is emptied faster when horses eat forage than when they eat concentrate. In contrast to other monogastric animals the mucosal surface of the equine stomach is divided into three types of glandular epithelium and the upper part of the stomach is lined with squamous epithelium. In the squamous section, which comprises almost half of the stomach, microbial fermentation by lactic acid producing and lactic acid utilising bacteria occur. The glandular epithelium produces mucus, hydrochloric acid (HCl) and protein degrading enzymes which together are called gastric juice. HCl lowers the pH and the microbial fermentation stops and the activity of the protein degrading enzymes increases. The pH varies greatly between the different parts of the stomach and values from 1.11 to 7.57 have been measured.

Gastrin is an hormone which stimulates secretion of gastric juice in the stomach and a Swedish study has shown that voluminous meals like forage gives a rapid and large increase in gastrin release. Small meals like concentrate gives a slower response in gastrin. This indicates that gastric distention plays an important role in inducing gastrin release during meals. The highest concentrations of gastrin were measured when the horses had free access to forage and then also maintained even and high levels throughout the observation period. When the horses instead were given a limited amount of forage and concentrate the gastrin levels decreased to fasting levels after a few hours. To summarize, a lot of forage, preferably free access, is important for our herbivores.

Sara Muhonen, AgrD

References:
Frape D. 2008. Equine Nutrition and Feeding. 3rd edn. Blackwell Publishing Ltd. UK.

Meyer H, Ahlswede L & Pferdekamp M. 1980. Investigations on stomach emptying and the composition of stomach content in horses. Dtsch. Tierärztl. Wschr. 87, 43-47.

Sandin A, Girma K, Sjöholm B, Lindholm A & Nilsson G. 1998. Effects of differently composed feeds and physical stress on plasma gastrin concentration in horses. Acta Veterinaria Scandinavica 39, 265-272.

Varloud M, Fonty G, Roussel A, Guyonvarch A & Julliand V. 2007. Postprandial kinetics of some biotic and abiotic characteristics of the gastric ecosystem of horses fed a pelleted concentrate meal. Journal of Animal Science 85, 2508-2516.

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