I can’t tell whose/what kind of liability you are asking about, but yes.
Anyone you are paying to care for your horses needs to have liability insurance. Worst case scenario: he leaves a gate open, the horses get out and cause a car wreck in which people are injured or killed.
Here is the info on the policy that my farm sitter has. Every year she sends me the coverage certificate. https://www.petsitllc.com/pet-business-insurance-options
They used to have language about horses somewhere on their site but I couldn’t find it today. I emailed the company and they confirmed
Per the insurance underwriter:
The PSA program policy provides coverage for the caring of all domestic pets, including dogs, cats, rodents, reptiles, birds, fish, etc. The PSA program policy also provides coverage for the caring of horses and other “farm animals” as long as they are considered pets and are not intended for farm use. For example, the policy would provide coverage for caring for a pet goat, but it would not provide coverage for a cow meant for slaughter or chickens used for eggs.
If he’s only doing this for you and doesn’t want the added expense, then maybe you could offer to pay for the policy. At $200/year it’s worth the peace of mind IMO.
I’m also assuming you’re in the US. The old forum used to show a location, I can’t find it in this one. 