Due to the risks of potential breast cancer down the road, most vets will recommend you spay before the first heat which is around 6 months. However, breast cancer is not that common in Aussies. Recent work with Golden Retrievers and Shepherds has shown that spaying them before 6 & 1/2 months might put them at greater risk of developing orthopedic problems such as torn cruciate ligaments. It’s now thought in those breeds to wait until they are closer to 2-3 years of age before spaying. However, no work has been done on Australian Shepherds and this theory does not apply to all breeds. So until such work is done, I would still recommend spaying before and around 6 & 1/2 months of age.