Comparison of grass haylage digestibility and metabolic plasma profile in Icelandic and Standardbred horses.
Authors: Ragnarsson S, Jansson A
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Ragnarsson and Jansson (2011) investigated whether breed differences between Icelandic and Standardbred horses might explain their divergent metabolic responses to forage, particularly given the Icelandic breed's historical adaptation to sparse nutrition. Six horses of each breed were fed two grass haylages of different maturity stages in a crossover trial, with faecal collection for digestibility analysis and plasma sampling for metabolic profiling on day 24 of each 24-day period. Contrary to expectations, the breeds showed similar digestibility of crude protein, neutral detergent fibre and gross energy, although Standardbreds did digest organic matter more efficiently; notably, Icelandic horses gained weight on both haylages whilst Standardbreds lost weight under identical feeding conditions, accompanied by higher plasma total protein and insulin but lower urea concentrations in the Icelandic horses. These findings suggest that breed differences in energy partitioning and metabolic efficiency—rather than superior fibre-digesting capacity—underlie the Icelandic horse's superior ability to maintain positive energy balance on limited forage, a distinction with implications for nutritional management, conditioning programmes and metabolic disease risk assessment across different breeds.
Read the full abstract on PubMed
Practical Takeaways
- •Icelandic and Standardbred horses respond differently to identical haylage despite similar digestion rates—feed management and ration design should account for breed-specific metabolic tendencies, not just digestive output.
- •Icelandic horses naturally tend toward weight gain while Standardbreds tend toward weight loss on grass haylage; caloric intake targets should be adjusted accordingly to prevent overfeeding or underfeeding.
- •Monitor plasma insulin and urea as markers of metabolic efficiency when comparing individual horses' responses to forage; these biochemical markers may reveal metabolic type better than digestibility coefficients alone.
Key Findings
- •Organic matter digestibility was significantly higher in Standardbred horses compared to Icelandic horses, despite no differences in crude protein, NDF, or energy digestibility.
- •Icelandic horses gained weight on both haylages while Standardbred horses lost weight, indicating breed-specific metabolic responses to the same feed.
- •Icelandic horses had higher total plasma protein and insulin concentrations but lower plasma urea, suggesting better energy retention capacity despite similar digestive efficiency.
- •Metabolic differences between breeds appear independent of digestive capacity, with Icelandic horses showing superior ability to maintain positive energy balance.