The key to being ready for summer, is starting in the spring. If needed, replace the blades to any mowers - sharp blades make for cleaner cuts which increases the health of your grass. Go ahead and start building your fly control arsenal. If you haven't already done so in the last 6-8 weeks, deworm your horses. Winter does not stop parasite cycles, and infact with little grass to eat, the horses are more likely to pick up parasite eggs off the ground while foraging.
Spring is the best time for yearly vaccinating, for several reasons.
The biggest reason being that your best immunity from many of the vaccines is during the first 2-3 months after they are given. Other disease like rhino and flu are transmitted from horse to horse. During the spring and summer many folks are out more, trail riding, showing, etc. Even if you don't go anywhere with your horses, and are fortunate to live where mosquitoes never roam, please check your rabies vaccination records and make sure your horses are up to date with this important vaccine. Rabies has broken out in several different areas of late and there is NO CURE once your animal has contracted the virus.