I know that Ivermectin can be used topically on guinea pigs for lice & mites. Is, I have Ivermectin 1% for Cattle/Swine (I use it on goats). Is this also safe for guinea pigs, topically behind ears and on rump? Thanks for your help!

goatlady, the Ivermectin that you have is the same one that is used in the treatment for all animals. I have used it on dogs and cats. I know that it is cleared for guinea pigs but the problem is dosage amount. It is so easy to give a gp an overdose. Simply applying it topically, still allows it to get into the blood stream through both the skin and by your gp cleaning himself. I don't feel comfortable telling you that a certain dosage is correct without your vet's input. Therefore, I would strongly advise you to call your vet and bring your little one in for an examination and discuss course of treatment. If you are living in an area where it is difficult to get to a vet, here is a website dedicated to guinea pigs. They do discuss ivermectin and it's uses, I am including that page as well, but they also advise speaking to a vet first, as I have done here. I cannot in good conscience, tell you that you should follow their dosage advice. I am including these links to aid you in your search for information.
Guinea Lynx :: Parasites
Guinea Lynx :: Ivermectin