The effect of very low food intake on digestive physiology and forage digestibility in horses.
Authors: Clauss M, Schiele K, Ortmann S, Fritz J, Codron D, Hummel J, Kienzle E
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Equine digestion has traditionally been characterised as a rapid, low-efficiency system compared with ruminant digestion, yet the practical consequences of severe feed restriction on horses' digestive capacity remain poorly understood. Clauss and colleagues conducted a controlled study using four ponies fed grass hay at four intake levels (ad libitum, 75, 55 and 30 g/kg⁰·⁷⁵/day) across two hay types of differing quality, measuring mean retention times (MRT) of digesta and nutrient digestibility. Although MRT did increase substantially with lower intake—ranging from 23–31 hours at ad libitum to 38–48 hours at the most severe restriction—digestibility of organic matter and neutral detergent fibre paradoxically declined, dropping from 43–47% and 37–42% respectively down to 28–35%, suggesting that prolonged fermentation time alone cannot compensate for severely reduced nutrient availability to the hindgut microbiota. The findings challenge the assumption that horses benefit digestively from extended transit times during underfeeding, implying instead that below a critical intake threshold, the limiting factor shifts from fermentation kinetics to absolute nutrient supply—a distinction with significant implications for managing horses in periods of forage scarcity and for understanding the metabolic consequences of poor-quality or restricted diets in clinical and performance contexts.
Read the full abstract on PubMed
Practical Takeaways
- •Very restricted feeding (below 55% normal intake) paradoxically reduces digestive efficiency in horses despite longer digesta retention, meaning severely limited diets extract fewer nutrients—not more—from forage
- •There appears to be a critical intake threshold below which horses cannot maintain body condition; this challenges assumptions that prolonged feeding times compensate for low food availability
- •Hay quality matters: late-cut hay (lower protein) produced finer faecal particles and different digestibility patterns, suggesting feed type selection becomes increasingly important during restricted feeding periods
Key Findings
- •Mean retention times for particles <2mm increased from 23-31 hours at ad libitum to 38-48 hours at 30 g/kg(0.75)/day intake
- •Apparent digestibilities of organic matter and NDF decreased substantially at very low intake, dropping from 47/43% and 42/37% at ad libitum to 35/35% and 30/28% at DMI30
- •Below a critical food intake threshold, the limiting factor for digestion is nutrient supply to gut bacteria rather than fermentation time, despite increased retention time
- •Ponies maintained body weight at 75% normal intake but lost significant body mass and condition at 55% and 30% intake levels