NAF Oestress. Oestress Powder compliments the mare’s natural oestrus cycle by encouraging regularity and providing extracts of herbal ingredients that have been used for hundreds of years to support hormone balance. So by improving her diet with Oestress, you are helping your mare to help herself. Oestress also provides bio-available magnesium to relax muscle tension and encourage calmness. Lastly, Oestress is rich in natural antioxidants to naturally support a healthy system. Oestress should be fed daily throughout the spring and summer season and may be increased in accordance with her oestrus cycle. However, if needed Oestress is suitable for year round use.