Hi there XXXXXXXXXXX,
Thank you for your question regarding your 3 year old Lab Retriever who has a relatively large bare spot on his chest! As you can imagine there are quite a number of things that could be going on here, however as he likes lying under the deck (laying on probably dirt or stones) it is more likely he has a chronic rubbing irritation and/or a contact allergy.
Firstly - you need to make sure that your Lab is definitely up to date with flea control and please make sure you are using a flea product appropriate for his weight. Even though you cannot see any fleas on him doesn't mean there are one or two lurking and oftentimes this is all it takes for a dog with flea allergy dermatitis. In your dog's case it does sounds like he has an allergy of some sort, however this could also be caused by parasites or fungi (ringworm or yeast).Bascially dogs are allergic to four main things - food, fleas, grasses/plants (contact allergy) or environmental allergens (canine atopy - the dog version of ezcema). I am sure you have worked through all of these with your Veterinarian, but I always like to ensure I have talked through each of these with my clients here in New Zealand. Flea allergies are avoided by strict flea control - every 3 - 4 weeks with Advantage or Advantage Multi or every 5 - 6 weeks with Frontline. You must also ensure all dogs in the household are treated at the same time. For a food allergy, you will need to undertake a food trial with a 'novel protein' diet such as Hill's Z/D ultra allergen free and needs to be fed SOLELY for 3 weeks. After this time if you are seeing a change in your dog's allergy you can slowly introduce different foods week by week with the guidance of her Veterinarian. Contact allergies are best treated by avoidance of the plants that are to blame, but identifying the exact cause of a contact allergy can be very hard. A referral to a canine skin specialist may be the way to go in this dog's case for either a skin patch test or a blood allergen test.
It is also possible your lab may have skin mites or lice as they commonly cause intense itching and irritation. These could be either Demodex (less itchy) or Sarcoptes mites (VERY itchy) and you should ensure a full Veterinary check up so that he or she can carry out a physical examination and possibly a skin scrape to check for mites and lice, as well as signs of fleas. The next step would be to double check for fungal disease (such as ringworm) and there are several tests for this including a UV light and a fungal culture. It could also be that your Lab has a bad yeast problem - and a good medicated shampoo such as Malaseb may well do the trick! Again a full Vet check will be able to confirm or deny this. If after these tests there is no diagnosis, the next step would be to carry out a food trial as above.
Thanks again for your question. Definitely keep on top of the flea treatment and use a good medicated shampoo (from a Vet or pet store) for him and you could also try some topical antibiotic cream rather than your wash you have at home. Ideally you would take your boy to the Vet soon so that an exact diagnosis can be made here in order to help treat the problem. As I say, I am most suspicious of an underlying contact allergy here, but only a full Vet check could rule this suspicion in or out.
Best of luck with your Lab and please do keep me updated with your progress.
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Kind Regards,
Dr M D Edwards
Dog Veterinarian
Veterinarian - BVSc (DVM equivalent) - Webmaster & Head Veterinarian for www. onlinepetdr.com