Safe flea treatment for Collies

Rough Collies and several other herding breeds carry the MDR1 gene mutation — sometimes called ABCB1 — which makes them sensitive to certain antiparasitic drugs, including ivermectin and milbemycin at higher doses. It's a genuinely important thing to get right, because some popular combination products contain those ingredients and can cause serious neurological reactions in affected dogs. The good news is there are safe, highly effective options. To point you to the right one: is your Collie mainly dealing with fleas, or are ticks a concern too? And roughly how much does she weigh?

Good instinct to be cautious. The safest class of flea and tick treatments for MDR1-affected breeds are the isoxazolines — that's the active ingredient group behind products like NexGard, Bravecto, and Simparica. These work on the insect nervous system in a way that isn't affected by the MDR1 mutation, so they don't carry the same risk. For a 28kg Collie with your kind of mixed exposure — regular fleas, occasional ticks — I'd suggest NexGard Spectra in the 15–30kg range. It covers fleas, ticks, and also treats lungworm and some intestinal worms, which is useful if she's eating grass or in contact with slugs. One chew a month. Has she had any flea treatments before, and did she react to anything?

Advocate contains imidacloprid and moxidectin — moxidectin is in the same family as ivermectin, and it is flagged as risky for MDR1 dogs at higher doses. The fact she tolerated it is reassuring, but it's still not the recommended choice when safer alternatives exist. Not every MDR1-positive dog reacts, but you can't predict who will. NexGard Spectra avoids that uncertainty entirely. It's a soft beef-flavoured chew, most dogs take it happily, and the 15–30kg pack covers her weight perfectly. You can pick it up through your vet or online — it's prescription-only, so you'll need a vet authorisation, but if she's due a check-up anyway it's straightforward to get prescribed.

A few things worth knowing: give it with or just after food — it absorbs better with a meal and reduces the small chance of a stomach upset. Make sure she's been treated for intestinal worms recently before starting, as NexGard Spectra handles ongoing prevention but isn't a one-off dewormer for heavy existing burdens. And if you haven't already, it's worth asking your vet to run a DNA test for the MDR1 mutation — it's a simple cheek swab and means you'll know for certain rather than managing on assumption. Once you know her status, any future vet or groomer treating her can make informed decisions quickly.

Sounds like a good plan. NexGard Spectra monthly, given with food, and get that MDR1 test logged on her records — it'll save you having this conversation every time a new vet asks about parasite treatment. She's in good hands.