Equid Nutritional Physiology and Behavior: An Evolutionary Perspective.
Authors: Clauss Marcus, Codron Daryl, Hummel Jürgen
Journal: Journal of equine veterinary science
Summary
# Editorial Summary The evolutionary success of equids once rivalled that of bovid ruminants, yet modern horse species diversity pales in comparison—a disparity traditionally attributed to digestive inefficiency and reproductive constraints. Clauss, Codron and Hummel reframe this narrative by reconceptualising equid and ruminant digestion not as fundamentally opposed systems (hindgut versus foregut fermentation) but as convergent evolutionary solutions, both optimised for high chewing efficacy and feed intake. Counter to conventional wisdom, there remains no empirical evidence that equids digest poor-quality forage more effectively than ruminants; rather, the ruminant forestomach sorting mechanism proves superior, forcing equids into a morphophysiological strategy dependent on greater absolute feed intake to meet energy demands. A critical distinction the authors emphasise is that equids, uniquely among most herbivores including coprophageous species, cannot harvest microbial biomass from their gastrointestinal tract as a secondary nutrient source, potentially rendering them more vulnerable to feed scarcity and nutritional shortfalls. For practitioners, this perspective suggests that equine nutrition should prioritise strategic feed provision and quality rather than assuming horses possess innate advantages for subsisting on marginal forage—a reorientation particularly relevant when managing animals under resource constraints or formulating diets for clinical conditions affecting intake capacity.
Read the full abstract on PubMed
Practical Takeaways
- •Equids require consistently high feed intake to meet energy demands; any interruption in feeding availability poses greater nutritional risk than in ruminants, necessitating careful management of forage quantity and quality.
- •The traditional concept that equids are better suited to low-quality forage lacks empirical support; feed quality and quantity management should prioritize meeting high intake requirements rather than relying on forage 'efficiency.'
- •Understanding equids as a distinct morphophysiological solution rather than inferior competitors to ruminants can inform more appropriate nutritional and management strategies aligned with their evolutionary biology.
Key Findings
- •Equids and ruminants represent convergent evolution of high chewing efficacy rather than fundamentally different digestive strategies, with ruminants achieving superior efficiency through forestomach sorting mechanisms.
- •Equids do not utilize microbial biomass from their gastrointestinal tract, unlike ruminants and other hindgut fermenters, representing a significant physiological distinction.
- •Equids depend more on high feed intakes than ruminants to meet energy requirements and may be more susceptible to feed shortages due to less effective digestion.
- •Equid cranial anatomy enabling simultaneous forage cropping and grinding chewing may be unique among herbivores and represents a distinct morphophysiological adaptation.