My horse suddenly has a big lump on its back. Should I worry?

Check for bite marks (snake bite). If you cannot find any, there is likely some problem with a tooth or tooth root, or salivary gland. Your horse could also have been kicked there or, when eating, have bitten in some foreign material in the hay that could have caused a mouth injury. If the swelling does not go down within 24 hours I would call out a veterinarian for an exam of your horse's mouth and face.

It is most likely a cyst but of course I cannot be 100% sure just by looking at a photo. I suggest you just monitor it for now. If it becomes larger or starts to bother her you should have your vet out to check her. Cancer is unlikely.

Lumps in dogs are typically either some sort of mass, a cyst, an abscess, or the result of some trauma causing localized swelling. In a young dog like Rocky, I would be concerned about any of the four of these if it is as large as a human hand (even a small hand would be concerning!). I would be particularly concerned if you believe this could have popped up in a small period of time. Anything extremely fast-growing, whether it is a mass or an abscess, should be addressed swiftly as it could continue to grow, ulcerate and burst. Hope this is helpful!

These skin lumps can arise from a few different causes and they are usually not a big concern. The first thing I would check is if Juna has had any vaccines or injections lately. These are often give in the back near the shoulder blades and can sometimes swell a bit. They also sometimes get these from bites or other trauma. In these cases, the lump is just some fluid buildup under the skin. These usually start going down within a couple of weeks. Other causes can be from a blocked gland, fly warble, abscess or a tumor. You can safely wait a week or two to see if it goes away on its own. If it continues to grow of doesn't go down, then it's best to take her into the vet to get it checked out.

These may be swollen lymph nodes. Lymph nodes can swell and get very painful when they are inflamed. You need to get a veterinarian out for an exam. There may be some infection in the region that drains into those lymph nodes. Please call a veterinarian for an exam.

Based on your description it sounds like Colin may have suffered a puncture wound with something in his rear end. The lump you are seeing could either be some purulent fluid building up inside, or it could be a foreign object that is still inside (whatever it was that caused the puncture). If you are feeling significant amounts of heat emanating from the affected area, it is likely there is an infection brewing. The area may have to be lanced, drained, and then the horse treated with systemic antibiotics. The dragging of the left toe is hopefully not related to an ascending infection to a joint, but instead I hope it is just from a generalized pain from whatever Colin is feeling. If you have some bute or banamine around the house, I would consider using some until you can get a vet out to come and check things out. Hope this helps!

Any bump that appears quite suddenly like that should be evaluated by a veterinarian. It could be an abscess, or a cyst, or a tumor. The vet will likely start with a fine needle aspirate, which is where a needle is inserted into the lump and a sample of cells is taken to look at under the microscope. This will help to diagnose exactly what is going on with Zeus.