Your dog’s breath can smell like metal or iron due to blocked anal glands.
Their glands release a metallic smell when they get full.
However, various health issues, gum disease, ulcers could also be the reasons behind the metallic smell in dogs.
Both male and female dogs can develop metallic smelling breath.
It could be something harmless like; your pet ate his poop or chewed on something sharp that caused internal bleeding.
Moreover, an iron-like smell could also mean that your dog was trying to groom itself by licking his anal glands’ secretion.
Common Causes of Bad Breath in Dogs
- Periodontal Disease
- Kidney Disease
- Toxic Plants
- Pica and Coprophagia
- Anal Gland Abscess
Poor dental condition is one of the reasons for halitosis in dogs.
The condition may be caused by not cleaning your dog’s teeth frequently and not replacing toothbrushes regularly.
If nothing is done to prevent the tartar, it will keep build up and cause a thick layer of plaque on their teeth.
This plaque builds up to the point that it pushes the teeth away from their gums. 
As a result, the plaque creates enough room for bacteria to grow inside the mouth and gums, leading to bad breath along with gum infections and tooth cavities.
Root infections, cavities, and gingivitis are the result of bad oral hygiene. 
Note: Dogs can develop lesions, masses, and oral tumors, due to bad oral hygiene.
If your dog’s breath smells like pee/urine or ammonia, there are higher chances that it is a sign of kidney disease.
There is a science behind this fact.
If your dog’s kidneys don’t work properly, their urea doesn’t get eliminated.
The leftover urea, when stays in your dog’s body for a long time, causes a urine-like or ammonia smell in their breath.
Kidney diseases can also cause due to poor oral hygiene.
Dental disease in dogs will progress to continue and become advanced when they overproduce the bacteria and germs in their mouth.
These germs and bacteria get ingested in their system and penetrate the bloodstream, which causes liver and kidney damage over time. 
In case your puppy’s breath smells like rotten cheese, it is possible that it might have eaten a poisonous plant.
It is quite common in dogs to chew or eat plants if they are having stomach problems, as it helps to make them vomit.
Domestic dogs, on the other hand, lack the ability to distinguish between poisonous and non-poisonous plants and often consume the toxic ones.
As a result, their mouth emits an acidic or rancid odor.
In some situations, dogs are able to remove the toxic plant from their bloodstream on their own; otherwise, veterinary help is required. 
Did you Know?
Sago palm, Tomato plant, Aloe Vera, Ivy, Daffodil, Milkweed, Castor bean, Tulip, Begonia, Oleander, etc are toxic plants for dogs.
It’s possible that your dog has diabetes if their breath smells like acetone or chemicals.
Diabetes could also result in making your dog’s breath smell extremely sweet, just like your breath would smell after having a cup of extra sweet tea.
If your dog is diabetic, it will lack insulin.
Without insulin, your dog will have a tough time breaking down the carbohydrates it consumes.
The dog’s body begins to break down fat in order to obtain the essential sugars.
This causes the dog’s body to enter ketosis, which produces ketones as a by-product.
These ketones tend to smell like acetone, which results in your dog’s breath smelling like chemicals. 
This could be a very dangerous condition that may lead to the dog’s blindness, fatigue, and dehydration.
It needs to be treated as soon as possible and with caution.
Pica and Coprophagia
Coprophagia and Pica are two canine eating diseases in which animals try to eat inedible items.
As a result, their breath smells exactly like the things they have consumed from, paper to their poop.
Pica is an act of consuming inedible things like paper, plastic, wood, shoes, etc.
Many dogs try to eat rocks, toys, to even cloth.
This could be risky because the small pieces could cause them to choke.
Coprophagia, on the other hand, is a less pleasant term for a dog’s habit of consuming their poop or of other species.
This is the reason why your dog’s breath smells like poop sometimes.
Although Coprophagia can affect dogs by infecting them with viruses and bacteria found in their feces, it does not always result in the animal’s death.
Note: Pica and Coprophagia are caused either by poor training methods or the dog’s behavioral traits. 
Anal Gland Abscess
Anal gland abscess is a common and very painful infection in dogs.
Pus starts to build up in the sac during an infection.
The abscess could appear on one or both sides of the dog’s anus as a red, painful, and hot swelling.
In case the abscess opens up, a large amount of bloody or yellowish-green pus is released.
The infection will rapidly spread and cause serious damage to the rectum and anus if left untreated. 
If you suspect that your dog is having an anal gland abscess, you need to call your vet as soon as possible.
The vet will clean and treat the abscess.
It should be treated immediately as it can help to minimize the discomfort and swelling in that area.
Next time, if you smell iron or metal-like odor from the breath of your dog, observe their body and mouth thoroughly.
Give your dog a nice bath, brush their teeth properly, and then check if the smell has gone or it is still there.
If you suspect any signs of injury or swelling, then try to take your pet to the vet immediately.