Is it his food causing the rash?

I am just wondering if anyone has had a similar experience;

Bentley is now 4 months old and since we got him I only noticed him 'bum-skiing' a couple times and put it down to worms, so treated for that, but never saw any. I then noticed some dark patches (dark on the skin like dried on mud that's been there a few days) on his hind leg and him nibbling and scratching, so gave him a flea treatment. A small patch had since appeared on his belly.
We took him to vets on Friday for his second rabies jab and showed the vet the rash. He instinctively said it was his food, but then checked his anal glands.
Bentley let out a welp and then there was watery brown muck on the tissue, quite a lot (he's only a Jack Russell!)

The vet has said to leave it a week and if the rash is still there to change his food. It's been 6 days and another patch has appeared on his forehead. Does anyone think I should leave it a little longer before changing his food or have any experience of this anal gland thing?

He is currently on Hills Science Plan for puppies.

It sounds like the anal glands needed emptying and hopefully that should do the trick. Hill's Science Diet is one of the best available, but accasionally a dog is hypersensitive to it's ingredients so see how the next week goes. A rash like that can be a sign of a food allergy but predominantly shows an anal gland issue so hope that was what it was. Some people find if their dog is sensitive to the "decent" food availble, Chappie tins tend to suit better. Although some people don't like it, it is recommended for dog's with sensitive tummies so could be a thought - anyway keep us posted and good luck x

Thanks Ally! We ideally don't want to change his food as other than that he is happy on it (and silly OH bought another bag when we didn't need it so we have loads!!)

We have to go back the vet in a few weeks to get his rabies blood test done, is it something I should ask the vet to check regularly? And do you think he can show me how to do it?
I feel really bad that all this time it was his glands, poor little boy. Do you have experience of this? I just read that adding bran to his food can help firm the poop so that the glands are squeezed naturally..?

No matter how good or bad a food is, if your dog develops an allergy to one of the ingredients, you need to change to a different food. The Science Diet is the usual lamb and rice formula? You may not need to do any more than find a chicken or beef based food. I won't suggest any specific brands. I wouldn't go to one of the expensive, grain free foods until I saw if getting away from the lamb was all you needed.

The anal glands are the most common cause of the scooting. Some dogs have to have them emptied from time to time.

I agree; some dogs are just sensitive to certain products in food. A rice and kibble based food is better for sensitive tummies, but before you go changing the food I would see how he goes until you see the vet again next week as if it was his anal glands, then things should improve. Some dogs never need their glands emptying and some need them doing frequently. If you are good with that sort of thing your vet might show you how to empty the glands yourself - it isn't difficult just a case of squeezing the right place and knowing what you are feeling for.

My poor little lad has had his glands emptied twice this year. The first time they were infected so he had anti-biotics. Second time I assumed it was same thing but its not clearing up properly / keeps recurring, so my vet also thinks it could be an allergy. I've been told to cut out everything except his main food - no treats - and see if it clears up. He's on JWB junior, which is supposedly hypoallergenic

We have decided to change his food after closer inspection of the ingredients of Hills (too much corn for my liking) and as there's been no real improvement to the rash. I was going to go for JWB, but have chosen F4D after rave reviews by a lot of members on here. I will keep JWB as my reserve choice if things don't work out on F4D. I really feel like I've let Bentley down

Thank you all for your advice ♥