Now, here is some text I copied from a champion dog breeders site. Could be 1 of 3 things according to them:
QUOTE
Sometimes dogs will roll in the grass or in something smelly right after getting a bath. Some dog shampoos have perfumes that may be pleasant to humans but smell awful to the animal. It is just an effort to mask the unpleasant and un-dog-like odor.
Wolves will often roll in decomposing carcasses or the feces of plant eating animals or herbivores. This would mask their own scent and enable them to sneak up on their prey without detection. It could even fool members of the other species into accepting it as one of their own. This ancient instinct may have carried over to domesticated dogs.
Another school for thought is that dogs may roll in smelly things to 'advertise' what they have found to other dogs.
Mmm! What was he rolling in?
Rolling in their own feces or that of another dog is not as common and actually may be distorted behavior or a way to get attention.
What to do
Although rolling in something smelly is not desirable behavior, you should not punish the dog for doing what is only natural. It is better to try to prevent the chances of the behavior by keeping an eye on your pet. Fortunately, the behavior seems to diminish as the dog gets more mature.
Also, if it happens after a bath, you might try a different, unscented shampoo.
Dogs that roll in dog feces or their own may be seeking more attention and just doing something like that to get some sort of attention.
In conclusion
Dogs will usually roll in smelly or rotting things to mask their own smell, whether it is unpleasant to them or due to some natural instinct
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