Horse digestion vs human digestion:
• Meals vs Grazing. Humans are conditioned to have set meals throughout the day. On the other hand, horses are designed to eat, chew and digest constantly through the day and night.
• Stomach acid production: In humans, the production of stomach acid is stimulated by the presence of food in the stomach. Meanwhile, horses produce gastric acid 24/7 – regardless of whether there is food in their stomach or not. An over supply of stomach acid is one of the main causes of ulcers in horses (LINK). It’s also the reason experts suggest that horses ALWAYS have access to forage.
• Humans have a complex system of mechanical and chemical breakdown to help digest food. Meanwhile, horses rely primarily on bacterial breakdown to break their food into digestible molecules. When horses have an empty stomach, these bacteria die – which stuffs up the digestion of their next ‘meal’. This is why probiotics are so essential in horse care and especially the rehabilitation of starved horses.
• Relative stomach sizes. Horse’s stomachs are pretty small compared to the rest of their body. This is why it’s not ideal to feed large ‘meals’ as opposed to a constant trickle of feed. Us humans have a stomach that has the ability to expand 4 times it’s usual size. This is why our system copes so well with ‘meals’ throughout the day.
• Horses have a muscle that stops them from vomiting. This means that if food (and acid) needs to escape they reflux into their oral cavity.
• Salivary production is not constant in horses, as it is in humans. Saliva is alkaline, and it’s a great buffer against stomach acid. If a horse doesn’t receive enough roughage, they wont produce enough saliva to keep their stomach acids in check. Without that buffer, ulcers can develop.