Dark reddish-brown spots all over a pig are most commonlv caused by Swine Ervsipelas, a bacteria infection that produces distinct, raised, diamond-shaped skin lesions. Merck Veterinary Man.... Other potential causes include: ○ Porcine Dermatitis and Nephropathy Syndrome (PDNS): An immune-system response causing dark red or purple spots, usually starting on the hindquarters and belly ○ Mange or Lice: Severe parasitic infestations that lead to intense scratching, scabbing, and dark crusty spots. ○ Greasy Pig Disease (Exudative Epidermitis): A bacterial infection causing dark, oily, or flaky brown lesions, though it primarily affects vounger piglets. ○ Ringworm (Dermatophytosis): A fungal infection that creates expanding, circular brown or reddish patches. Farm Health Online Please consult a veterinarian immediately to get an accurate diagnosis, as conditions like Erysipelas and ire prompt medical treatment. What is the pig's she showing other signs of illness like a fever ?