New research has found that ponies can adapt metabolically to changes in haylage within just five days, with the nutritional composition of the forage playing a significant role in how their digestive systems respond.
The study, published in the Equine Veterinary Journal on 6 October 2026, was conducted by Professor Meriel Moore-Colyer, Simon Daniels and Pat Harris, with research carried out at the Royal Agricultural University and Hartpury University.
Changing forage is recognised as a potential risk factor for digestive disturbances, including colic. However, relatively little is known about how quickly the equine digestive system adapts when horses move between different types of haylage.
What Did the Researchers Investigate?
The study involved eight healthy Welsh Mountain ponies fed four different haylages, including ryegrass and mixed-species meadow haylages harvested at different stages of maturity.
The ponies were transitioned between haylages over three days, with researchers collecting urine and faecal samples to investigate changes in metabolic activity and hindgut function.
The results showed that the ponies had adapted metabolically to their new haylage within five days, with no major additional changes observed after this period.
Importantly, the structured three-day changeovers did not cause significant disruption to hindgut metabolic function in these healthy, forage-adapted ponies.
Forage Composition Makes a Difference
One of the most significant findings was that the chemical composition of the haylage, rather than simply its classification as ryegrass or meadow haylage, influenced digestive responses.
The greatest metabolic differences were observed between a younger, more digestible ryegrass haylage, which contained higher levels of water-soluble carbohydrates and less fibre, and the other three, more mature haylages.
Researchers also identified differences in metabolites associated with fibre fermentation and protein digestion.
Interestingly, the younger ryegrass haylage appeared to provide more protein available for digestion and absorption in the small intestine than the more mature forages, challenging the assumption that conserved forages are uniformly poor sources of available protein.
What Does This Mean for Horse Owners?
Although the findings suggest that healthy, forage-adapted ponies can adjust relatively quickly to changes between haylages, the researchers emphasise that caution is still needed.
The first five days following a change appear to be particularly important, as this is when the greatest metabolic adjustments occur.
Horse owners should therefore monitor appetite, droppings, consistency of faeces and general comfort when introducing a different haylage, particularly in horses with sensitive digestive systems or underlying metabolic conditions.
The research also highlights the importance of understanding forage composition.
Even haylages that appear similar can differ considerably in their sugar, fibre and nutritional content depending on grass species, maturity at harvest and growing conditions.
Having forage analysed can help owners make more informed feeding decisions and identify potentially significant nutritional differences when changing suppliers or batches.
Does This Mean Three Days Is Enough to Change Forage?
Not necessarily.
The researchers found that a structured three-day transition maintained metabolic stability in the healthy ponies studied, but the findings should not be interpreted as a universal recommendation.
All eight ponies had been maintained on forage-only diets for several years, and the study did not investigate more abrupt changes or transitions between different forage types, such as hay and haylage.
Horses receiving additional feeds, or those with digestive sensitivities, may respond differently.
The researchers conclude that while metabolic adaptation to new haylage can occur within five days, careful management and monitoring remain important, particularly during the initial transition period.
The findings provide further evidence of the importance of forage analysis and informed feeding decisions in supporting equine digestive health.
