You should look in Bohemia also; it's just south of Central Islip, also borders Connetquot State Park with its riding trails, and many properties are zoned for horses. IMHO many parts of Bohemia are nicer than some parts of Central Islip. There are quite a few large (1/2 to 1 acre or more) lots in Bohemia also.
Do a search of the MLSLI website for Bohemia; the listings should indicate if a particular house is "horse property" or not. Here's one that might interest you. By the way, the phrase "taxes are without STAR" means that your actual taxes will be somewhat lower after the S(school) TA(x) R(elief) discount is applied. There are two levels of STAR: the Basic, which everyone gets, and the Enhanced which is available to senior homeowners.
http://www.mlsli.com/uniDetails.CFM?...tart=21&rpp=20