The effect of very low food intake on digestive physiology and forage digestibility in horses.

The research is about exploring the impact of restricted food intake on the digestive physiology and forage digestibility in horses, a previously uninvestigated area. The study reveals that lower food intake does not enhance the horse’s digestive efficiency as previously assumed, pointing out a distinctive threshold wherein nutrient supply to gut bacteria becomes the primary concern.

Study Details and Methodology

• The study involved four adult ponies with an average initial body weight of 288kg. Two trials were performed using different types of grass hay diets, one mid-early cut with crude protein of 10.5% and neutral detergent fiber of 67.6% (hay1), and the other late-cut hay with crude protein of 5.8% and neutral detergent fiber of 69.5% (hay2).
• The ponies were given these diets at four different dry matter intake levels: ‘ad libitum’ (as much as they wanted) and at restrained rates of 75g, 55g and 30g per kg(0.75)/day.
• The research focused on investigating how digesta mean retention times (MRTs) and fiber digestibility varied with reduced dry matter intake levels

Observations and Findings

• Ponies managed to maintain their body mass on the unrestricted (‘ad libitum’) intake level, but experienced weight loss and deteriorated body condition when intake was limited to 55g and 30g per kg(0.75)/day.
• MRTs, particularly of particles smaller than 2mm, were found to be inversely proportional to the dry matter intake (DMI), varying from 23 to 31 hours on the ad libitum intake to 38 to 48 hours on DMI30.
• There was a decrease in digestibilities of dry matter, nutrients and fiber components when the intake levels dropped from DMI75 to DMI30. Apparent digestibilities of organic matter and NDF respectively dropped from 47/43% and 42/37% on the ad libitum intake to 35/35% and 30/28% on DMI30.
• Differences observed between the two hay diets included higher estimated ‘true’ protein digestibility for hay1 and finer fecal particles on hay2, with no differences in fecal particle size between intake levels.

Conclusion

The study concludes that there is a certain food intake threshold in equids below which the primary digestion constraint shifts from fermentation time to nutrient supply to gut bacteria. This threshold and its effects might vary between feeds and could potentially indicate differences between ruminants and equids.