If horses or livestock are allowed to continue grazing late into the fall and early winter, the grasses are eaten too close to the ground and weaken the pasture grasses. Grazing grass below three inches stresses the plant by reducing the leaf surface which grasses use to make their own food, thus forcing them to use up food reserves stored in their roots. Eventually, the grass depletes its stored reserves and dies, leaving bare spots in your pastures.
Utilize a "sacrifice area" so your horses or livestock can still get outside on nice days, but don't have full access to the pasture. Even though the weather may be nice, the soil conditions are often too wet to support the weight of your animals and they cause soil compaction and additional injury to the pasture grasses.
Preventing overgrazing will solve many of the problems pasture owners face. Bare spot and weeds are a result of overgrazing, either in the winter or summer. Before you spend more money and time reseeding your pasture, reevaluate how you are managing your livestock. If your stocking rates are high, like most of the pastures I see, utilize a sacrifice area all winter and during the growing season when the pasture growth has slowed to maintain a healthy productive pasture.
When you get the lawn mower out in the spring, that's the time you can also reintroduce your horses or livestock back to the pasture for short periods of time.
There are ways to extend your grazing season into the early winter. Additional planning and management is needed to achieve that. Penn State Extension has suggested strategies to extend your grazing season.
Now is the time to start thinking about your pastures for next spring.