For the collies and such, the preventative is USUALLY ok, but the deworming dose is way too high, and they will be seriously affected.
For those who use the paste, DON'T. You have no way of accurately measuring, and it will cause considerable damage, if not death.
On the heartgard package, divide the amount of active ingredient by the weight of the highest pound dog on the package, and that is your highest safe dose per pound you can use of the injectable. Be warned, the injectable is in milligrams per cc, not micrograms, so a small mistake is a 1000 X overdose.
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If you are not good with numbers (not willing to bet your dog's life on your mathematical genious)ask you vet to calculate the correct dose for your dog. If they won't do it, ask them why?
Most are not greedy. They just don't want to be resposible for your dog dying when you screw up your calculations.
ps, the injectable is in liquid form, however, it is given oral for prevention, never injected.