@jengosmonkey - NuHeart only does Heartworm, Heartguard Plus has meds for roundworms & hookworm. And people that give heartworm for 6 months are typically people that live in climates that have a cold winter, ie: when the ground freezes. We do not have that in this part of No. California so I give it year round.
Thimerosal in vaccines
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Interesting read:
http://www.dogsnaturallymagazine.com/thimerosal-in-rabies-vaccines/