Every horse goes through diet changes. Grass grows and dies back with the seasons, hay batches vary, horses move yards and injuries bring sudden box rest. The hindgut copes well with change when it is gradual, and less well when it is sudden. This page explains why, looks at the most common changes owners face and sets out how to manage each one. It is editorial guidance from Horse Probiotics, and horses with a history of laminitis, colic or metabolic disease should have any change planned with their vet.
Why changes unsettle the gut
Different feeds favour different microbes. A study by Dougal and colleagues showed that adding a starch-rich or oil-rich feed to a hay diet altered the faecal bacterial community, and research in the Journal of Animal Science found that an abrupt increase in starch lowered caecal pH and shifted bacterial populations over the following week. When the diet changes quickly, the existing population has to adapt quickly too, and fermentation can be disrupted while it does.
The link between change and colic is well recognised. A systematic review from the University of Nottingham, published in PLOS ONE, found that changes in feed had the largest body of evidence among management-related risk factors, including changes of concentrate, changes of hay and changes of diet overall. Recent changes in housing came second, with the studies that found the effect describing changes within two weeks or less. The authors concluded that avoiding changes, or introducing them gradually, should be a key part of preventative care. Redwings gives the same advice in its colic guidance: introduce changes to a horse's diet gradually and with care.
Managing the most common changes
A new batch of hay or haylage
Even hay from the same field can differ between cuts and years. Where possible, blend the old and new forage over around two weeks, gradually increasing the proportion of the new. Buying a larger batch of the same forage reduces the number of changes through the year if you have dry storage. A forage analysis can help if you need to know the energy or sugar content, and our article on how much forage a horse needs covers quantities.
Spring and autumn grass
Fresh grass is a big change from winter hay, both for the hindgut and for horses prone to laminitis. Build turnout up gradually, starting with short sessions and extending them over several weeks, and keep forage available when the horse comes in. Monitor weight and condition closely. A study by the Animal Health Trust, the Royal Veterinary College and Rossdales, reported by World Horse Welfare, found that weight gain more than doubled the risk of laminitis, and that weight was often gained unintentionally even when owners were trying to maintain or reduce it. Horses with short morning grass access and those wearing grazing muzzles for only part of their grazing time were also more likely to develop laminitis, which the researchers took as a sign that some grazing restrictions were not working as intended. Native ponies and their crosses, and animals with a previous episode, were among the higher-risk groups.
Moving yards
A yard move often changes forage, water, grazing, companions and routine all at once. Take a supply of your current hay and hard feed so that you can blend the change in over a couple of weeks, keep feed times similar, and give your horse time to settle before asking for hard work.
Box rest
Sudden box rest after injury removes grazing and exercise at the same moment, and Redwings lists prolonged confinement as a possible stress trigger for colic and laminitis. Your vet will set the rules for the recovery period. Within those, keep forage available for as much of the day as possible, adjust hard feed to the reduced workload and watch droppings closely.
From living out to stabling
The autumn move from grass to hay or haylage, often combined with more hours in the stable, is one of the largest changes most UK horses face each year. It helps to start offering conserved forage while your horse is still grazing, so the hindgut meets the new fibre gradually rather than overnight. Our article on winter gut health covers this switch in more detail, including water intake and overnight forage.
Planning ahead
Because so many changes are predictable, a simple yearly plan goes a long way. Note when your grass usually starts to grow strongly in spring, when you normally bring horses in for winter, and when your hay supply is likely to change. For each of those points, decide in advance how you will blend forage, how turnout will be built up or reduced, and how you will monitor weight. A weigh tape used at the same time each week gives a far more reliable picture than the eye alone, particularly under rugs.
If more than one person feeds your horse, write the plan down in the feed room. Consistency between helpers matters as much as the plan itself, and a clear note avoids a well-meaning extra scoop or an early switch to new haylage.
Where supplements may or may not help
Predictable changes are the situation where a gut supplement is easiest to justify. Many products suggest starting a week or more before the change and continuing until the new diet has settled, and our guide on how to feed a probiotic explains timing and introduction. The evidence is still mixed. A review of live yeast in Animals found contradictory and variable results, and a review of probiotics in the Journal of Veterinary Internal Medicine described the evidence for clinical efficacy in horses as weak.
A gut supplement cannot prevent laminitis. Laminitis risk is managed through weight, grazing control, diet and veterinary testing for underlying metabolic conditions. Our gut balancers guide explains the ingredient types, and the best horse probiotics comparison and the reviews hub help you compare products by strain, inclusion level and cost per day.
Signs to watch during a change
- Looser droppings, or free faecal water after a forage change
- Reduced appetite or reluctance to eat new forage
- Rapid weight gain or a hardening crest during the spring flush
- Reluctance to move, shifting weight or heat in the feet, which can indicate laminitis
- Any signs of colic