As several people on here have mentioned in the comments some border collies are sensitive to this product. From what I have read in the past, ALL breeds of collies may have a gene that makes them sensitive to Ivermectin, a common heartworm preventative. Other herding breeds such as the GSD are also reported to have this gene. However in GSDs it is much lower, only about 10% of them have it. If you are concerned I would recommend talking to your vet, there are also tests they could take to see if your dog carries this gene. However after reading about this product it says it uses imidacloprid and moxidectin as the active ingredients. I do not know the effects of these ingredients on herding breeds.
This post is pretty old, so I am not sure if anyone will read this. I have an allergic dog and it is NOT food allergies. If you can solve your dog’s allergies by diet then you are lucky. I have struggled with my dog allergies for years and I can offer some helpful advice. Also, I just had to put my dog back on steroids after several years and I can say the side effect are bad (the reason I came here). Anyway, I found a pretty good solution to manage my dogs allergies. You need to give the dog a bath every week using Ketochlor shampoo followed by a hydrocortisol shampoo. I put a video up on YouTube about it that nobody watches. Search for “Solution for itchy dog Nutfork”. I really hope this can help you! Dog allergies are really frustrating!