Estrogen is pretty well studied in being beneficial towards healing.
Estrone is used therapeutically in conjunction with appropriate work and other treatments. Its not an either/or treatment.
In of itself it is not a miracle fixer, and I definitely wouldn’t only use estrone and expect a brilliant recovery.
Rehab is not just stall time plus time put back to work. It is comprised of many different steps as the body goes through the trauma and subsequent recovery that is acute injury, condition loss, and reconditioning/recovery: it has a thousand little parts – one part time off, one part healing, one part unlearning ‘destructive’ muscle memory, one part reconditioning the body and new (correct) muscle as old muscle memory dies off, one part correct conditioning work to improve stability or muscle memory, and one part management (or many).
Here is how it was explained to me by the vet, although it’s been years and some things may not be remembered faithfully: Estrone (estrogen) helps with muscle building and improving collagen in connective tissue. It is anabolic (assists in the building of new muscle tissue) and helps mildly with stiffness associated with inflammation. It’s a hormone, so it has a significant behavioral component and is especially useful in behavioral cases – with unlearning pain responses while introducing correct work.
This is, IMHO, the real reason estrone is used for rehab cases – it helps the horse be more tractable in correct work. If the horse is still in pain, or still compensating because of muscle memory, or untractable because of pain memory, you end up back at square one because without ever unlearning the compensational habits of the horse, you continue to put strain on the injured area.
In rehab, the horse has to learn to use their body in a way they have never had to before (or for a long time) – doing these body building exercises after months off in a stall is hard. It can be painful. Estrone helps keep them more relaxed while helping physically to build correct muscle.
Besides all that, it has virtually no negative side effects and it’s dirt cheap. It’s used a lot in my area (Area 1) with positive results. 