
Thank you for your query,
The product that I would recommend to help your horse build condition is NRM LowGIsport. NRM LowGIsport is unique to most ‘cool feeds’ as it has a higher calorie level therefore perfect for your horse to help gain condition. NRM LowGIsport contains no cereal grain with the majority of calories being derived from ‘cool’ energy in the form of fat and fibre. The sources of the ‘cool’ energy include the super fibre beet pulp, lucerne and the high fat stabilized rice bran supplement KER Equi-Jewel (which will help the coat). NRM LowGIsport also contains a KER premix which means at the recommended intakes your horse will receive its daily requirements of vitamins and minerals except salt (so you can remove the multi mineral block if feeding a recommended rate). You can continue to supplement the MgO but be very careful that you do not over supplement this mineral.
I would recommend introducing NRM LowGIsport to the mare slowly gradually building up to the recommended rate over a 2 week period. It sounds like you are supplementing enough roughage (hay, chaff and pasture) but keep in mind the ideal amount is 1.5% of her body weight per day. If the muscle stiffness is being caused by nutritional tying up then NRM LowGIsport is extremely safe in that regard.
I hope you find this information useful.