Grass seed abscesses
It is not uncommon for the sharp awns of grass seeds to work their way under the skin and cause a large pus filled swelling. It is the long sharp pointed type of seed that has minute barbs like a tiny arrow head that only allow it to move forward through the body tissue that cause the problems.
They occur most commonly in late summer or autumn and can affect any dog, though most commonly longer haired active dogs that are exercised in reserves or long grassed areas.
The seed can get caught in the coat and works its way down to and then though the skin. Once it is under the skin the body tries to eliminate it and pus is formed that can swell into an abscess. Sometimes the entry hole can heal over leaving no clue to the source of the problem.
Common sites include between the toes and in the cheek (coming from the inside of the mouth) though the seeds can end up any where, even in the middle of muscle tissue. Once under the skin they can keep migrating - even moving 10 - 20cm or more!
Often dogs will need to have a general anaesthetic and the vet will need to explore the tissues surgically to find the offending seed - This can be quite a challenge but need to be done.
In extreme cases a seed might migrate through muscle tissues and into the spinal cord - with very serious consequences.
To prevent problems a concerned owner should check the pets coat after an outing where a dog may have picked up seeds. Focus between the toes and in thick hair on the dogs underside - prevention if definitely better than cure.