How can you clean feathers so they're safe for cats to chew on?

My cats love to eat feathers as well. However, when I asked my vet about it, she said that I should not collect feathers outside and give them to my indoor cats for playing (and possible eating). She said that the hollow shaft can contain harmful bacteria/diseases which are especially dangerous for indoor cats. (I cleaned the feathers I collected by pouring boiling water over them but it seems that is not enough. I also think it's important to consider that outdoor cats usually get vaccinated more extensively and/or their immune system is different.)

Now I sometimes buy peacock feathers from a small webpage that spends earnings to treat cat diseases, so I feel somewhat safe about them and my cats like those for playing as well. I don't think that it is important for them to actually eat feathers.

The only two thoughts I had (boiling or baking, both which will heat the inside of the shaft as well as the outside) are both confirmed by this page, which states (edited for formatting):

Dry Heat

1. Turn oven to 230 degrees Fahrenheit (110 degrees Celsius).
2. Place feathers 4 inches apart on a cookie sheet. This allows hot air to circulate freely around each feather.
3. Bake for two and a half hours.
4. Remove from oven to cool.

Boiling

1. Place feathers in a saucepan.
2. Add water to cover the feathers and be 1 inch above them.
3. Heat the water on high heat until it bubbles.
4. Boil for 20 minutes. Some fungus spores may survive this treatment.
5. Reshape the feathers gently with your fingers. Their fibers will compress from the boiling action.

Boiling step 5 is obviously only really relevant to crafting. In any case, heat sterilization doesn't involve chemicals and should treat the inside as well.

Heat sterilization is a common technique. Note that dry heat sterilization, according to the CDC:

The most common time-temperature relationships for sterilization with hot air sterilizers are 170 °C (340 °F) for 60 minutes, 160 °C (320 °F) for 120 minutes, and 150 °C (300 °F) for 150 minutes.

So if you want to go by the CDC you might try baking at 300 °F or higher, but monitor carefully as I do not know at what temperature feathers would begin to melt or burn. I believe dry heat sterilization is generally done by blowing hot air, so if you do not have a convection oven you may want to increase the baking time and/or temperature slightly.

The 230 °F baking / 212 °F boiling temperatures from that site are a bit low, although I am not familiar enough to give you any real solid info on what those temperatures kill and what survives.

That said, some obligatory disclaimers:

• I have no scientific information backing the end results of feather sterilization through these processes. Even the WHO mentions: "Since the achievement of the absolute state of sterility cannot be demonstrated, the sterility of a pharmaceutical preparation can be defined only in terms of probability."
• I have no idea if feathers release anything toxic when heated, although my gut says no, I am not sure.
• I have no idea if instrument / pharmaceutical sterilization techniques are appropriate for feathers.
• I'd still be worried about feathers as a choking hazard, regardless of how clean they are.

Really I'd just get your cat a nice fluffy toy.

If feathers are from a toy, you mustn't let your cats eat them, because they are full of chemicals (and maybe avoid to buy them, and make a diy one)

Yes, ingesting feathers is a normal diet and instinct for predator like cats, they ingest everything, fur and feather, especially the soft feathers.

Ingesting feather can be dangerous when the feathers are not soft, but big and spiky, it can make some trouble to the stomach. If a cat has a weak digestive system, it's a thing to monitor. Some cats may caugh, but usually when the feather can't be digested, is eliminated by caughing.

In the nature, feathers are not boiled or clean or bacteria-free. Except if the feather comes from a particularly dirty bird, like a diseased one, it shouldn't be a problem, and rather reinforce its immune system. Things don't have to be too clean.
The danger is rather the chemicals in feather toys, and you can't wash that kind of things.

You talk about " bleach, soap, borax, hydrogen peroxide, alcohol, etc."

That's really more dangerous and hurtful than natural microbiote on feathers!

To have natural feathers, don't buy them, collect them. If someone you know has birds or chickens, just take the natural feathers (not too spiky or attach them very strongly), and clean them with only water, but anyway, you must choose clean feathers, found in a clean place (not in the poo by example).

Boiling feathers is the only thing you can do if you are very paranoid about the natural microbiote. Remember, cats are natural animals, a too dirty environment and a too clean environment are both nocive. And just remember that chemicals that can be released when you boil or heat a feather that has been dyed or chemically treated, is more nocive than the virus and bacteria found on normally healthy animals.

There's no 100% riskless way to decontaminate feathers, feathers can't be sterile or stay sterile for a long time.

I find natural feathers during the summer, which I take home and clean by first making sure all the rough stuff (if any) is off the quill part. Then I wash them in Dawn dishwashing detergent, soak them in clean water, rinse them well, and air-dry them.

I only give the feathers to a cat when I am around to supervise, and if they break one, I take that feather away and give another. If they try to eat them or tear off pieces, I take them away and wait another day before offering a new feather.

I also make sure I am giving a large feather like hawk's, turkey's and on occasion an eagle's, never a small bird feather.

I think the ideal way to sterilize something is to put it into a pressure cooker for 20-30min while pressurized.

As far what is a acceptable diet for a cat you must recognize - your cat is not a wild cat. While it may be safe for a wild cat that has been hunting birds since they were young to eat a feather, it may not be the case for a house cat who is not used to that.

Also even for a wild cat, I imagine eating a large feather can be problematic.

You can clean the feathers under hot running water, wrap in paper towel and microwave 1 to 3 minutes. If they are too brittle don't let your pet have them, microwave less if the change texture or color.