Complete senior feeds are feeds with more digestive nutrients and high fiber. Dr. Worth explains what complete feeds are, what senior feeds are, and how complete senior feeds work.
Feeding senior horses is much the same as feeding other horses: 24/7 access to hay is essential. However, you may need to add in a probiotic and feed a higher quality hay for your older horses.
Horses that are underweight are a special challenge in the cold. They need hay and plenty of it, but they will need really good quality hay, probably second cut, or mixed with some legume hay. They will need the higher feed value of the better hay, as well as the benefits of the bacterial fermentation.