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.
I bought a collar for each of my dogs recently, unsure whether they would have an effect or not. My one dog has niggling hips and knees which have of late caused her issues after long walks. It was heart-breaking to see her want to go but then to suffer afterwards. My terrier had cut down the walks that she wanted to go on with us too. I did not want to commit either dog to a life of medication so opted to try a collar. I am incredibly pleased to report that both dogs have improved dramatically in just three short weeks, I wish I had bought the collars before. My terrier is back to full gusto with her walks and the lab/husky is back to her puppy state despite rising 9. I am so pleased that they have their personalities back long may it continue!!
Size of Dog Body Weight Approx Daily Amount Toy 2kg - 3kg 30g Toy 3kg - 4 kg 40g Small 4kg - 6kg 40g - 60g Small 6kg - 8kg 60g - 80g Small 8kg - 10kg 80g - 100g Medium 10kg - 12kg 100g - 120g Medium 12kg - 14kg 120g - 140g Medium 14kg - 16kg 140g - 160g Medium 16kg - 18kg 160g - 180g Medium 18kg - 20kg 180g - 200g Medium 20kg - 22kg 200g - 220g Medium 22kg - 24kg 220g - 240g Large 24kg - 28kg 240g - 280g Large 28kg - 32kg 280g - 320g Large 32kg - 36kg 320g - 360g Large 36kg - 40kg 360g - 400g Giant 40kg - 50kg 400g - 500g Giant 50kg + 500g max