I talk often about the importance of high omega 3:6 ratio Salmon and other fish oil for breeding dogs.
There has been some discussion online recently about the possibility of supplementation with salmon and other fish oil depleting vitamin E.
This post takes a deeper dive into that topic so you can ensure you are supplementing your dogs properly and also not causing any harm when you do so.
There’s a single small (n=25) study that shows a small reduction in vitamin E in humans that supplement. It only showed this effect in younger women, not in women older than 35. It's not the most robust study I've seen. It has a small sample size, no controls, and doesn't even have a crossover design.
There’s no study about salmon oil and vitamin E in dogs that I could find. Different species metabolize nutrients differently, so it's important to not extrapolate things like this (especially things that aren't even really proven in humans and are the result of one small, flawed study) from humans to dogs.
That all said, let's pay devil's advocate and assume it's a concern for dogs.
The overall issue is less vitamin E specific and more antioxidant specific. Fatty acids are oxidized in the body. This can deplete ANY antioxidant, including vitamin E, but also many others.
So the answer to this is pretty simple: ensure adequate antioxidants.
Not all fish oils have preservatives. Most that do use tocopherols, which are a form of vitamin E.
The tophoperols have two purposes: 1. Act as preservative to prevent oxidation/free radical production in the fish oil (which would in itself deplete vitamin E), and to supply vitamin E.
Having a good supply of antioxidants should prevent any issues (not that there are even proven issues, but assuming there are, this is the way to avoid them).
I personally feed a food with added vitamin E and other antioxidants, I use a topper that is high in antioxidants, and I use a fish oil that has the highest omega 3:6 ratio on the market and is preserved with vitamin E (preventing oxidation even before it gets ingested).
While antioxidants are important, like many other things too much isn't always better. Antioxidant toxicity can happen, Vitamin E and A toxicities are rare, but possible. And excessive levels of antioxidants can negatively impact fertility, including male fertility.
Your best bet is to find food and supplements formulated by veterinarians and PhD animal nutritionists. A good food should have the antioxidants you need to keep your pet healthy. Not all food is, so this is definitely a question to ask when you look at a food.
If you aren't sure your food has adequate antioxidants, one of the best supplements is to simply give your dog a few raspberries, blueberries, or blackberries a day. One for a small dog, 3 for a medium dog, and 5-6 for a larger dog.
Feel free to drop me a line if you have questions about this other other breeding nutrition topics.