l have a mastiff and theres a terrible odour coming from

Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.

Most often, this odor is due to the secndary pyoderma caused by a drematitis. This may be due to allergies causing this hair loss and pyoderma which is an infection that has a very bad odor. Since you know it is not anal glands, the treatment for this is as follows:

Give Benadryl at 1 mg per pound every 12 hrs for 10 days.
Apply Betadine to the areas that appear red or irritated or where there is hair loss every 8 hrs. Clip away all the hair in this area. This is a skin infection called a pyoderma caused by the irritation that, in turn causes this odor. These can both be purchased at the pharmacy over the counter.
Bath weekly with Malaseb or Dermaplex which will remove the scabs or flakes. This can be purchased at the pet store or online.
If there is no response, then your vet will have to run tests such as skin scrapings and cultures to determine the cause and then they will treat according to these results.

This breed is also prone to Thyroid issues that can cause skin issues. Your girl may be too young for this but your vet will test for this.

Does that make sense to you?

Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.

Sincerely, ***** *****