Lumpy rash

[Cathy18]

My 25yr old gelding has developed a lumpy rash across his shoulder. Its been there 6 days now and is gradually getting worse and spreading across his chest to his other shoulder. The lumps are hard and vary in size a lot. If you can get through his hair some have a little scab on them. There is also heat coming from the rash. He's on spillers senior mix to keep his topline as he loses weight very easily. This is given with nuts, beet, vegetable oil and extraflex. This diet has been the same for 12 months. We had a laminitis scare about 3-4 weeks ago so he also went on Global Herbs LPS. This has now been stopped in case he's reacting to this
Its been suggested that they are protein lumps/bumps? What can I do about them and are they anything to worry about?

 

[Tiffany]

I'm not expert by a long way although could be an allergic reaction to something. Have you changed anything else apart from adding the herbs to his feed.

 

[Cathy18]

Nothing that coincides with the rash :-( he's had a new lightweight rug, using a maintenance mix rather than conditioning mix but this was way before or after it started?