We used it several years ago .At that time we bred 3 females and none of them took. I had read a article at that time that said Valbazen could be the cause. I have no information to prove this as a fact but we stopped using it and the next cycle all 3 females had litters of pups although with a different Male. Just a thought.
I've got to note that this got my attention as after decades in beagling i've got a mother and now daughter that are exhibiting what appears to be sugar fits after 4 or so hrs of hard running. 1st time ever. Since its a mother and now a daughter i was thinking that confirmed genetics. But have been really studying the ingested tick meds and now the occasional valbazen ive used. This showed up about the time i started using valbazen and now in a daughter right after her 1st valbazen treatment. I've tossed the valbazen and going back to the basics. And i have abandoned those 2 for breeding which is disturbing as they were very good up untill the sugar fit or whatever hits.
Been using it for years. Never give it to pregnant females. Use safeguard for them and puppies. Also change wormers for a while. Have heard the same from others but my vet that I have now uses it. Has worked for me. Use what you are comfortable with.