A quick note about my recent experiences with mites - earlier this year I took one of my guinea pigs to the vet with mites, and his treatment of two 5 minute sessions and two injections cost me about £55.
Last week I found that another of my guinea pigs definately had mites, and three seemed uncomfortable, two with a couple of small cuts. I bought a product called Xeno 450 from the vets over the counter: 6 pipettes for just over £28. I have treaded all six of my guinea pigs with it, as well as bathing tham all in "Lice and Easy" shampoo from gorgeous guineas and washing all the cages/houses/carry box. thoroughly. (This took all day!)The vet advises that I treat them again in two weeks which I'm going to do.
If you're not sure that your GPs have mites, it's best to go to the vet for a consultation, but if you are sure, you may find it's cheaper, and easier on the guinea pigs (they get to stay at home) to use Xeno 450.
You do have a valid point there, but my personal opinion is that if you're at all unsure of a diagnosis and/or it's the first time you've come across a particular symptom/ailment, then you should always get it checked by the Vet. Then, with experience, if you're confident in treating something yourself without a Vet consultation then that's fair enough.
I also got "stung" the first time I encountered mites, as I was inexperienced and didn't know better. Took my 2 piggies to the Vet for a firm diagnosis but, as they'd run out of topical Ivermectin treatment, he gave them both an injection (telling me that the injection was more expensive but was all they had in. Great!). This 5 minute visit cost me £35 and I had to follow it up about 10 days later with another £35 (5 minute) visit....so it cost me £70 to treat both pigs.
If I'd realised then that I could've bought the Xeno spot on treatment myself for around £20 online then I would've used that instead, but I had no idea and at that time could only get a diagnosis from the Vet. (Tupeny, don't buy Xeno from the Vet, it's even cheaper online!) Now that I
do know what to look for, I feel confident in treating mites myself, at home, but it's only because the Vet helped me the first time.
Btw I've switched to a different Vet now, as this previous one wasn't very cavy savvy. I think this new Vet is still expensive but I feel it's worth it for specialist care. Don't assume that cheaper is necessarily going to be better, but if you can find a great Vet with inexpensive rates, then happy days!
