I'm sorry to hear that your pup isn't well. I know how worrying this can be, and certainly empathize.
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I don't think any of us can - or should - speculate as to what has happened, as we are not vets, and have not seen your dog. Unfounded speculation can lead to more harm than good.
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Do you believe your dog can manage until Monday, when vet practices re-open, or do you believe the pain is such that he needs an emergency appointment this weekend?
How did you leave it with the vet in Bern? Did he or she tell you when to come back if there was no improvement?
Did you feel comfortable with this vet? If so, I would go back on Monday, ask for a further assessment.
If necessary, you could ask for a referral to the Kleintierklinik of the University of Bern. This clinic is run by the Veterinary school, and has the bells and whistles for advanced diagnostics.
https://www.kleintierklinik.unibe.ch...index_ger.html
Now - while not outrageously expensive, be aware that specialist care will cost more. You will have to pay for a consultation to get started - a couple hundred perhaps - but before embarking on a course of treatment ask for a cost estimate upfront.
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I have had many ultrasounds and biopsies done with my mutts, for varying reasons - and the cost varies as well, depending on what is needed in an individual case.
But to give you a very rough idea of various veterinary costs in Switzerland, here are some published veterinary price lists. First, from a vet in Thun, from 2021:
http://www.tierklinik-thun.ch/filead...linik_Thun.pdf
And here is the general Tarriff list from the Tierspital at Uni Zürich from 2019 (maybe figure in a little more for inflation.) I couldn't find one for UniBE, but as they are both clinics run by the teaching and research universities I'd guess they would be similar.
https://www.rd.uzh.ch/dam/jcr:b6fbe1...Tierspital.pdf
As you can see you are probably looking in the low three figures for an ultasound.
If a biopsy is needed, a simple needle aspirate with a tolerant dog won't be too expensive. If sedation is needed, or if a surgical biopsy is needed, costs will be higher.
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If the local vet says that the condition is not time critical, can you return to Germany for treatment? It will likely cost less there.
If you can't get to Germany, can you arrange a video appointment with the vet you saw there? That shouldn't be too expensive and might bring you some peace of mind.
If the condition is urgent, though, if your dog is in significant pain, don't delay treatment - go to a local vet!
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This is bolting the barn door after the horse has escaped, but for the future, if you are worried about being able to afford an unexpected veterinary bill, you might want to look into taking out pet health insurance.
There are several threads on the subject, do a bit of browsing. Be aware, though, that pre-existing conditions are likely to be excluded from coverage, so run several scenarios to see if this is a sensible solution for you, or not.
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I am not in the BE area, my personal experience is with vets and clinics in the ZH/SZ/ZG area. Hopefully someone from the BE area will be along shortly with futher suggestions for area vets.
I hope you find answers soon, and that your pup recovers quickly.
Wishing you and your pup all the best.
ETA:
Just an FYI, there is a video veterinary consultation service, partnering with Meiko, the pet supply company. I have never used this, so please take it as information only, rather than a recommendation. Cost of the first consultation via phone or video is CHF 45 for a 10-15 minute consultation.
https://pet-care.ch
But were it me, I'd be back at the local vet on Monday - I'd want an in-person consultation.
Again, all the best.