Mares need to have both their own nutritional requirements met as well as those of the developing foetus.
 It is not until he 4th trimester that mares need to have their rations increased beyon d the norm or maintenance.
While many broodmares will be fed an appropriate commercial ration during their pregnancy, they may not be fed the amount specified by the manufacturer for a variety of reasons. There is often an over reliance on grass to meet the mares's nutritional needs.

Supplementation of copper, folic acid, calcium and phosphorous at appropriate levels during pregnancy reduce the incidence of developmental orthopaedic disease in the foal and it is essential that appropriate levels of selenium is available to the mare for a succesful and unassited delivery.

Other useful supplements include:
 

Garlic which is an effective anti-microbial plant acting on bacteria, viruses and alimentary parasites. It lowers blood pressure and improves cardio-vascular health and stimulates cell growth.

Equilibrate COMPLETE or CHF (older mares) provides all the elements and vitamins required in an available medium in the correct ratios. 

• Echinacea, is usefulo for the immune system and  has been successfully used to treat candida.