Grass-cracks or something worse? Cracked hooves in horses explained

standing for prolonged periods of time in damp conditions may lead to reduced horn quality. Although we cannot control the weather if at all possible during prolonged periods of wet weather horses should have access to hard standing or clean dry stabling.
Regular farriery will help to keep feet trimmed and balanced to reduce the risk of traumatic cracks
A trimming interval of six weeks is average but some horses may need more or less frequent visits to keep their feet in good condition. Occasionally it may also be necessary for your vet and farrier to work together and use radiographs to guide the shoeing process particularly in cases with a foot imbalance.
Some horses have poor foot conformation which can predispose them to damage. Breeding for good hoof conformation may help to increase horn and foot quality and biomechanics in future generations. 
Try to avoid excessive or fast work on hard ground 
This may lead to traumatic fractures of the hoof wall particularly if your horse is overdue for trimming. 
Supplementation may help to improve horn quality in some horses
Biotin may be valuable in some horses but it can take up to a year to notice a significant effect as the hoof quality will improve from the coronary band down. Supplementation with vitamins and minerals such as methionine zinc and calcium as well as omega3 fatty acids may also be beneficial in addition to a balanced diet. It is always advisable to ensure that your horses body condition is within the correct range to reduce the load on the hooves and to ensure optimal overall health. Bear in mind that not all horses will need dietary supplements. Speak to your vet about the available supplements to choose which one is right for you.