Fat digestibility in Equus caballus follows increasing first-order kinetics.

This research article explores the variant fat digestibility in horses (Equus caballus), attributing it to different factors and proposing that the process follows a first-order kinetic model. The research utilized data from 188 digestive balance observations, revealing a high true digestibility of fat and highlighting the potential of lipase kinetics and the fat content in food to influence the fat digestion efficiency.

Fat Digestibility and Contributing Factors

• The article discusses the variability of ether extract digestibility, which ranges significantly from forages to grains and added fats. An ether extract is a measure of fat content in feed dominated by triglycerides.
• Two main factors thought to influence this variability were:
  • The presence of nonhydrolyzable substances in the ether extract, especially in leafy foods.
  • The dilution of endogenous fecal fat. Endogenous fecal fat refers to the body-generated part of fecal fat content.
• However, data from numerous digestion balance observations in horses indicated that these factors were not sufficient to explain the difference between true digestibility and apparent digestibilities in basic feeds and partial digestibilities in test feeds.

A First-Order Relationship: Digestibility and Fat Content

• The researchers identified a third possible contributing factor: an increasing first-order relationship between observed digestibilities and the fat content of the feed.
• A significant first-order relationship was demonstrated, indicating that half maximum digestibility (46%) occurs at a fat content of 24 g/kg, which is common in forages.
• This finding is in line with the notion that fat digestibility or absorption efficiency might depend on the rate of lipolysis, especially when the residence time in the small intestine is limited.

Potential Implications and Conclusions

• The kinetic activity of lipases, which are enzymes responsible for fat breakdown but difficult to measure, could contribute to low digestibility when substrate concentration in the small intestine is low due to a low fat content in food.
• Implicationally, this research also indicates that the status of essential vitamins A and E could be affected by low dietary fat contents and might be improved by fat supplementation.
• In conclusion, this study suggests that understanding and optimizing fat digestibility in horses may require further investigation of lipase kinetics and dietary fat collections, in addition to known factors.