Why does my old dog sound out out breath all day?

Dog owners tend to dismiss bad dog breath as just "dog breath," but there is usually a very good reason behind the odor. The most common causes of bad breath in dogs are bad oral hygiene and periodontal disease.

https://www.akc.org/expert-advice/health/get-rid-of-stinky-dog-breath/

not enough information to guess, but I recommend an immediate visit to a veterinarian.

dogs noses are very sensitive organs and can sniff problems into the lungs
may have sniffed up the beetles eggs that have hatched in the lungs or other dust mite problems
An x-ray of the lungs would be the suggested test
However house cleaning and rug and carpet regular maintenance will diminish the problem for pets

It's how a dog keeps himself cool.

I had the same issue with my dog and I solved it by using dental treats which provide freshening breath and reducing plaque buildup and tartar formation.

There are many treat that promote dental health; for instance biscuits are extremely popular due to the fact they are crunchy and they help keep your dog's teeth clean by scraping off debris.

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Don't feed your dog raw hide bones. Horns/antlers are a better choice

To make DIY dog muzzle,use any long strip of material that you can find like ribbon, maybe some oldpantyhose or rope. From the dog's nose, loop it under the chin and tie into aknot. Take both ends of the materialbehind the ears then tie into a bow. Make sure it does not hurt the dog in any way and that it appears toserve its' purpose.