Heartworm Prevention -- Yes Or No?

A postcard from Gracie's vet arrived today:

It's time for Gracie to get an annual heartworm test and a supply of heartworm preventive medicine.

The annual heartworm regimen always makes me uncomfortable. It seems risky to give my healthy dog this medication every year. Yet the risk of her contracting a potentially deadly heartworm infection seems worse.

I give Gracie regular Heartgard for dogs. Regular Heartgard contains only ivermectin --- the antiparasitic medication that prevents heartworm disease. Heartgard Plus contains ivermectin and pyrantel --- to treat and control roundworms and hookworms. I've considered using Heartgard Plus because Gracie eats wild rabbit poop in our yard (click here to see a post about that) and I was afraid she would contract worms from the rabbits. Yet I had her tested for worms two separate years, and the results were always negative. So I decided Gracie doesn't need extra medicine to prevent worms.

According to the Heartgard Product Information Sheet (found here on the Heartgard website), "The initial dose must be given a month (30 days) after the dog's first exposure to mosquitoes. The final dose must be given within a month (30 days) after the dog's last exposure to mosquitoes."

I figure the mosquitoes in our neighborhood don't get active until May or June so I wait until late May or early June to have Gracie tested for heartworm and started on Heartgard. I give her Heartgard only four times a year instead of the recommended six doses per year, with the last dose at the end of August or the beginning of September. That protects her until around the beginning of October when the mosquitoes are just about gone.

The older Gracie gets, the more hesitant I feel about giving her heartworm meds. In spite of the way she runs and leaps around the yard, Gracie's an older dog. I'm not so sure what's riskier to her health: giving her potentially dangerous heartworm medication, or taking a chance that she'll get heartworm disease.

I'll take Gracie for a heartworm test soon and talk it over with her vet. I'll update this post after I decide what to do about heartworm meds this year.

***POST UPDATE: Click here to see what I decided.