Pregnant mares and foals on the move: how safe is transport?
What we know about stress, risk and best practice
Transporting horses is a routine part of breeding and racing life. But when the passengers are pregnant mares or foals, the stakes are higher. The physical demands of late gestation, the fragility of a young immune system, and the stress of the unfamiliar all combine to make careful planning non-negotiable.
So how risky is it really – and what does good practice look like?
Pregnancy and travel: when timing matters
While most mares travel without incident, the risk isn’t zero. In early pregnancy (the first 45 days), elevated stress hormones like cortisol can affect embryo retention. In late gestation, transport introduces risks like dehydration, fatigue, and – in rare cases – preterm labour. That’s why the mid-pregnancy window is considered safest for travel.
Physical risks also shift as mares approach foaling. A growing abdomen alters their centre of gravity and mobility, making abrupt movements more dangerous. Long-distance transport can add to this strain, particularly if the mare is dehydrated or not given regular rest stops.
Infections and biosecurity
One of the more insidious risks comes not from the trailer ride itself, but from what the horse might encounter along the way. Equine herpesvirus-1 (EHV-1) can cause abortion in pregnant mares, and it’s most commonly transmitted through horse-to-horse contact at transit farms or shared spaces. So vaccination protocols and strict biosecurity – disinfected trucks, no mixing with unfamiliar horses – are essential.
What about foals?
Foals are more susceptible to travel-related stress for one simple reason: their immune systems aren’t yet fully developed. That makes them more vulnerable to infections, fatigue, and dehydration. They also don’t regulate stress hormones as efficiently as older horses. Travel with a foal should be gentle, quiet, and well-prepared, with frequent breaks and access to hydration.
Even behaviourally, transport can be challenging. Foals may become unsettled when separated from familiar surroundings or herd mates. Bedding, partitions, and thoughtful trailer design can help them stay comfortable and stable during the ride.
What good practice looks like
Best practice for pregnant mares includes:
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Timing it right: Avoid transport during early conception or the last month of pregnancy.
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Minimising stress: Use familiar companions and experienced handlers.
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Regular breaks: Every 4–6 hours for rest and water.
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Vaccination and checks: Especially for EHV-1.
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Loading calmly: Noise and panic can elevate risk more than the trip itself.
For foals, it’s about:
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Safe trailer setup: Soft bedding, stable partitions, and enough space.
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Hydration: Frequent stops so foals can nurse or drink.
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Monitoring: Watching for signs of lethargy or distress.
What the science says
Research backs up what good stockpeople have long practised. A 2000 study by Friend showed cortisol (the stress hormone) spikes sharply within the first few hours of travel, but this can be reduced through calm handling and regular rest. Another study (Allen et al., 2007) found mares moved in mid-gestation, with vaccination up-to-date, had no increase in pregnancy complications compared to non-transported mares.
So is it safe?
Yes, if done right. Transporting pregnant mares and foals does carry risks, but they’re manageable with planning, oversight, and experience. It’s not the movement that causes harm; it’s poor preparation.
When horses travel in the care of people who understand those risks and put systems in place to reduce them, they arrive in good health – and sometimes better off for the trip.
