Rolling is predominantly a sign of a happy and healthy horse as an unhappy horse is unlikely to roll (see further down for exceptions). It can serve various purposes;
- grooming and external parasite control: a good rub relieves all those itches in hard to reach places and is the natural way they would try to relief irritation of parasites and flies, the mud or sand can create an extra weather barrier from sun or wind and cold -this is the reason I don’t brush my (un-rugged) horses every day but you still have to run your hands over them to check under the mud their skin is healthy and you are not missing any minor injuries hidden by the mud and horses with sensitive skin or prone to mud fever, sweetitch or general dermatitis should be managed slightly differently. It can be frustrating if you are rugging your horse at night and they have got covered in mud during the day but it is an important behaviour for them to be allowed to exhibit.
- scent marking and social bonding: as well as happiness at being re-united after 2 weeks of the ponies being in a weight reduction field (low grass but ad lib access to hay in slow feeder nets) the mutual rolling in the above images allowed the mixture of scent marking and re-establishing who is who (this was also displayed via some herd running and play before the rolling started.) Horses sense of smell is much greater than ours and they can communicate (like many other species) a lot of important information this way.
It is wonderful to watch and they all take their turns. It takes a lot more effort for the big horse to get down and he spends more time deliberating over which is the best spot, his high withers and back problems mean he can not roll all the way over which is said to be a good indicator of fitness and muscle, he must roll one side and then if he wishes get up, then lay on the other side to roll that side. Horses generally only go down to roll once (twice if they need to get up to turn over like this big horse) if they roll more than that there may be a problem; although rolling is normally only done by happy horses that have the majority of their needs met, they can also roll due to severe pain like colic where they try to relieve the gas pain, if you notice this then go closer to look – they will likely be starting to sweat and you will be able to see the discomfort and distress in the tension in their face. Call the vet immediately.
(If you are trying to practice clicker training with your horse, this would be the perfect opportunity to try to capture your horse rolling and/or laying down.)