Whether to administer heartworm prevention year-round or seasonally remains debated, with welfare and practical arguments favoring year-round administration in most endemic areas.
The welfare argument for year-round prevention centers on the consequences of missed doses. A single missed dose during transmission season in an endemic area can allow infection that, progressing silently for months, eventually causes cardiopulmonary disease. Year-round prevention removes the risk associated with forgetting to restart prevention, seasonal administration errors, and owner uncertainty about when the risk period begins and ends. For most dog owners in endemic regions, the simplicity of year-round prevention and the elimination of timing errors makes it the welfare-protective choice, even if biologically some seasons carry minimal risk.