Horses are amazing, they have many mechanisms to assist them in the harsh conditions. With the temperature starting to drop, the blood becomes slightly thicker and flows through the muscles at a lower rate. It is important to warm them up as cold muscles are biomechanically stiffer than warm muscles and can result in stiffness and soreness if warmup is not extended in colder times.
With more moisture in the air, frequent morning dew, slight amounts of rain (and increasing), horses hooves will absorb up to 15% more water and become softer than normal. This can create a higher risk of bacterial infection through the hoof wall if the structural strength is compromised. The hoof needs to be conditioned to keep it in good health, nutrition on the inside feeding all cells, good shape for equal balance on the ground via a good professional and additional nutrition applied topically to assist in reducing the water absorption yet feeds the cells nutrients.
This comes in the form of a moisturiser. Only use oils, creams moisturisers than have natural, readily absorbed ingredients like plant oils. Plant oils need to make up a higher percentage of the product. Additionally don't use products that have unnatural preservatives (usually a pesticide to kill bacteria growing in the product) as these chemicals assist in making the hoof dry and splinter the surfaces.
Winter time is a great time to watch out for swollen legs.
How do they happen can be a range of issues from messing around in the paddock and slipping on the surface, winter storms causing the horses to get excited and run around, horses in confinement due to bad weather may show signs of swelling as the ability to move around has been restricted, so regular movement is good. Good idea to have ice boots and poultices on hand in the home vet bag.
As the wet weather increases so does the mud and oportunity for that dreaded greasy Heel (Pastern Equine Dermatitis) so regular checking of the potential areas affected need to be viewed so if it does happen, you can quickly treat the area.
Another common problem with the changes in weather is the bacteria on the body like the idea of the moist warm conditions so they step up the breeding. With this comes the onset of Rain Scald. Easily treated, ensure the rugs are not to warm, remove them more often to allow the skin to breate in the air and treat with a good skin wash.
Apart from the above lets hope this winter is setback free.