Yes I know it requires at vets prescription, my chiropractor will sign for it.   What is an inexpensive feed to put weight on an older horse?  I have a 20 yr old mare that must have took a bad fall on the ice.  She blew out her stifle,badly sprained a fetlock(all on the left). Chiropractor said those injuries shouldn't make her none weight baring on that leg but she will not put weight on.  Chiropractor couldn't feel any broken bones but must have something broke or fractured.   Mare is in a stall but loosing weight 

thanks

https://www.boehringeringelheimequinerebates.com/#/promoselect

Not sure of the cheapest place but there's a $77 rebate on the 180 count bottle

X-ray and find the problem.

There are usually 2 reasons why a horse is non weight bearing :

abcess in foot

broken bone

some stifle injuries can be very painful

I'd have the vet check it out

I get mine from Valley Vet and they take care of asking the Vet for refills.  Also yes get Vet to x-ray.

Allivet for rx.  Second the advice, get xrays.