The development of a metabolizable energy system for horses.
Authors: Kienzle Ellen, Zeyner Annette
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary: Metabolizable Energy System for Horses Kienzle and Zeyner developed a practical predictive equation for equine metabolizable energy (ME) by systematically analysing how protein and fibre intake influence non-productive energy losses—work that had previously been poorly characterised in horses compared to ruminants. Through literature review, they established that urinary energy losses in horses correlate directly to crude protein intake at a constant rate of 0.008 MJ per gram, whilst methane losses are much smaller than in cattle and scale proportionally to crude fibre intake at 0.002 MJ per gram. Their adapted equation uses readily available feed composition data (crude protein, crude fat, crude fibre, and nitrogen-free extract) to predict ME from dry matter, allowing practitioners to move beyond generalised energy values and account for individual feed characteristics. For farriers, nutritionists, and veterinarians managing equine diets, this approach is particularly valuable because it recognises that forage-based diets generate higher urinary losses per gram of digestible protein than concentrate-based rations—a distinction that affects ration balancing, especially for sport horses and those with specific energy requirements. The simplicity of the calculation, requiring only standard feed analysis values, makes this system practical for field application whilst maintaining the precision needed for evidence-based nutritional management.
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Practical Takeaways
- •When formulating rations for horses, use the provided ME equation rather than assuming ruminant-based systems, as equine energy losses differ substantially due to hind-gut rather than foregut fermentation.
- •High-protein feeds (especially forages with phenolic compounds) incur greater urinary energy losses in horses; account for 0.008 MJ energy loss per gram of crude protein when calculating diet energy content.
- •Methane losses are minimal in horses compared to cattle; focus nutritional management on protein and fibre intake optimization rather than methane reduction strategies.
Key Findings
- •Renal energy losses in horses correlate more strictly to crude protein intake (0.008 MJ/g) than to digestible protein intake, with roughage sources causing higher losses than concentrates due to phenolic acids.
- •Methane energy losses in horses are substantially lower than in ruminants and correlate closely to crude fibre intake at 0.002 MJ/g, reflecting differences in hind-gut fermentation mechanisms.
- •A practical ME prediction equation was developed: ME (MJ/kg DM) = -3.54 + 0.0129×crude protein + 0.0420×crude fat - 0.0019×crude fibre + 0.0185×N-free extract.
- •Renal energy losses account for much greater energy loss than methane losses in horses, requiring specific correction factors when predicting metabolizable energy from digestible energy.