Black Diarrhea in Cattle: Differential Diagnosis & Herd Management

Melena (black, tarry feces) indicates digested blood from upper GI or specific infections/toxins.

Infectious Causes

• BVDV: Mucosal disease form → hemorrhagic enteritis, high mortality.
• Coccidiosis (Eimeria): Bloody diarrhea in calves 1–6 mo; oocysts on fecal float.
• Salmonella, Clostridium perfringens type A/C, EHEC: Hemorrhagic colitis.
• Rotavirus/Coronavirus: Usually watery; can be bloody with secondary invasion.

Nutritional/Toxic

• Copper Deficiency: "Falling disease," diarrhea, depigmentation, aortic rupture.
• Vitamin A Deficiency: Night blindness, keratinization, diarrhea.
• Blackleg (Cl. chauvoei): Acute myonecrosis; sudden death, crepitant swelling. Not primary diarrhea.
• Lead/Nitrate Poisoning: Neurologic signs prominent; GI hemorrhage possible.

Management

• Necropsy + lab (PCR, culture, toxicology) for index case.
• Hydration/electrolytes (oral/IV), NSAIDs for endotoxemia.
• Antimicrobials per culture/sensitivity.
• Correct mineral/vitamin deficits; vaccinate (BVD, clostridials, lepto).
• Biosecurity, sanitation, gradual diet transitions.