Do I need to dose my cows every year?

This is both farm and year specific. Rainfall largely governs the amount of parasites an animal is exposed to, so in years of low rainfall treatment may not be necessary (no symptoms/good yields all season), but this can change drastically in wet years – particularly in the case of lungworm where naturally immunity will dwindle in dry years, leaving animals very susceptible thereafter.

This is both farm and year specific. Rainfall largely governs the amount of parasites an animal is exposed to, so in years of low rainfall treatment may not be necessary (no symptoms/good yields all season), but this can change drastically in wet years – particularly in the case of lungworm where naturally immunity will dwindle in dry years, leaving animals very susceptible thereafter.