Disclaimer: This article is presented for informational purposes only and is not intended to endorse any product.
Hoof growth slows in winter for two major reasons. One is that cold weather results in less blood flow to the extremities. The other for most horses is less formal exercise in winter. Regular exercise can go a long way in reversing both effects.
Slower growth often means the intervals between hoof care get lengthened. This makes sense when there is little new hoof to work with, but there may be consequences. Nail holes enlarge over time, making shoes loose. Shoes that come off can take a piece of hoof wall with them.
Leaving shoes off in winter makes more sense and is also good for the feet, allowing the inevitable hoof constriction that comes with shoes to reverse. However, if hoof wall quality is not good there is the risk of chipping and cracking. Weak heels may also collapse and run forward, especially if the toes are not brought back appropriately. A longer interval between trims is only going to set the stage for and aggravate these issues. A few strategic swipes of the rasp to restore balance, round wall edges and back up the toe from above can make a world of difference.
If the hoof horn is healthy, you don’t have to worry about moisture from snow or mud being absorbed but poor quality, dry hoof horn will absorb both moisture and bacteria. Fat is an important component of the moisture barrier. The horse can manufacture fats when needed but a hay diet is significantly lower in fat than live grass. Supplementing flax seed to match the fatty acid profile of grass, up to 200 grams a day, may help.
Obviously if a horse’s hay had protein/amino acid and/or mineral deficiencies or imbalances in the summer, it does in the winter too. These can worsen, though, if you either feed less hay or less grain/balancer when the horse is not in work. New appearance of hoof horn quality issues or thrush over winter should prompt a nutritional consultation.
If you allow hoof problems to develop over winter you will pay the price when you want to resume riding in the spring. Attention to comprehensive care is cheap insurance.