Dog itching/biting

Hi! I have a 6 year old Australian cattle dog mix. In April, she bit a wound into her hind leg that was treated with antibiotics. The vet didn’t really know the cause. In May, she bit another wound into her tail. Was treated with antibiotics and the vet didn’t know the cause either. I’m afraid she’s trying to bite another wound into her other hind leg as the skin as already slightly broken. What would be the reason to be biting and scratching the skin so much? Allergies? She’s never done this before. No changes in diet. No environmental changes. No new meds or supplements.

Hello and thank you for this interesting case.  Dogs can self-harm for a variety of reasons;  common ones include parasites (its quite common to see dramatic effects from fleas or sandflies, for example, without ever seeing the guilty critter) or allergies, or pain.  This last one is often overlooked, but I have certainly seen dogs biting their paws to distract themselves from abdominal pain, for example.   Regarding allergies, the frustrating news is that dogs can develop them;  they can occur seemingly randomly at any age.  They can also develop due to miniscule changes in the environment that owners don't necessarily notice, including for example a new plant sending its pollen over the fence, or a certain insect, or something they sniffed on a walk.  In conclusion then, there's loads to go at and your vet should help to releive the symptoms and narrow the possible causes down.