From
http://princetonvet.net/can-skip-hea...icine-winter/:
Can I Skip Heartworm Medicine in the Winter?
We strongly encourage all pet owners to continue giving heartworm prevention medicines to their dogs and cats all year long. We do see dogs and cats with heartworm disease in our practice every year. These
incidence maps from the
American Heartworm Society show that we are in an area with a high number of cases of heartworm disease.
If you give your dog her dose of heartworm prevention on October 1, and she gets bitten by a mosquito on October 10, but you don’t plan to give her another dose of heartworm prevention until April 1, she could very easily get sick with heartworm disease over the winter.
Most heartworm prevention medicines
don’t just protect your dog (or cat) from heartworms. Some are also flea and tick prevention, and many protect against other intestinal parasites. Depending on the weather, these bugs and worms can be around in the environment all year long. Keeping up your dog’s protection against
intestinal parasites (worms) is an important part of keeping him healthy.
Remember, heartworm prevention is not only for dogs and cats who spend time outside. Mosquitoes can fit through screens or get in through open doors. When the weather turns cold, they are looking for ways to get warm! Make sure that your
inside pets are protected, too.