* Bruises: These can be caused by injury, especially if the pig is kept in a crowded or confined space.
* Blood clotting problems: This can be caused by a variety of factors, including infections, vitamin deficiencies, and certain medications.
* Skin infections: Bacterial or fungal infections can cause skin discoloration and inflammation.
* Parasites: Some parasites, such as ringworms, can cause skin lesions.
* Other medical conditions: There are a number of other medical conditions that can cause purple spots on a pig's back legs.
It's important to note that these are just some possible causes and that a veterinarian needs to examine your pig to make an accurate diagnosis. Please schedule an appointment with your veterinarian as soon as possible so they can assess your pig's condition and recommend the appropriate treatment.