When it is super icy there is not much you can do to prevent your horse from slipping. Your best bet to prevent injury is to leave them in until it softens or melts. Speaking of melting, there is mud! During muddy times it is very easy for horses to pull shoes. They also can develop skin conditions from the moisture against their skin. It is not always best to continually wash the mud off as this adds more moisture and if the horse has a full coat and furry legs it doesn’t dry well making the problem worse. When you wash your horses legs make sure you towel dry them and allow them to dry completely. Make sure you are checking for and treating thrush regularly also.
There is a significant amount of land management needed to handle winter weather and mud to keep turn out areas good year round. Even more so if you try to keep grass. All weather paddocks are a godsend if you have small areas to turn out or not much land. Keeping your horses off the grass in wet or muddy weather is key to maintaining the grass will be there when it is dry. Deep divots or torn up ground is not good when it refreezes. This is normal around the hay, water, or gates. If the paddocks are not large enough for there to be flat areas then those should be closed off when the ground is soft. Also over grazing of grass paddocks in the winter can damage the root system and the grass will have trouble returning well in the spring. The shorter your growing season the more impact there is.
The most important part of winter care for horses is they need to have shelter available when outside for long periods of time. They need to be able to stay dry or get somewhere dry. They must have hay and water available at all times, especially when outside as the temperatures drop. Water is the hardest thing about winter care. Frozen buckets, troughs and hoses can be a nightmare. Trough heaters and heated buckets can help so much. Make sure you drain hoses well after each use and/or bring them in somewhere warm to prevent them from freezing. You will be carrying some buckets as well. You may need to change their calorie intake in winter. Consider adding alfalfa cubes or chaffe hay to replace the grass they aren’t getting. There are many products out there.
No matter what climate you live in for the winter, horses grow a thicker coat as daylight hours decline. Different breeds have a tendency to thicker coats as well. Thoroughbreds and other hot blooded breeds typically have lighter coats while draft and cold blooded breeds grow a heavier coat. Then there are ponies. You can lose your hand in the depth of some of their fur!!