Acute Gangrenous Mastitis (Blue Bag) in Ewes and Does

Acute gangrenous mastitis, colloquially termed 'blue bag' in ewes and does, is a rapidly progressive, necrotizing infection of the mammary gland characterized by ischemic infarction, tissue necrosis, and systemic toxemia. It is most commonly caused by Pasteurella multocida (biotype A) or Mannheimia haemolytica (formerly Pasteurella haemolytica) in sheep, and by Staphylococcus aureus (often beta-lactamase producing) in goats, though other organisms such as Clostridium perfringens, Escherichia coli, and Klebsiella spp. may be involved. The condition typically occurs in the periparturient period, especially in high-producing dairy goats and in ewes with poor udder hygiene or trauma. The disease is a medical and surgical emergency, often resulting in loss of the affected mammary gland, culling, or death. Economically, it causes significant losses due to reduced milk production, treatment costs, increased labor, and premature culling. In flocks and herds, it can be a sporadic but devastating problem, with morbidity up to 10% and mortality up to 50% in severe cases if untreated.

The primary etiological agents of acute gangrenous mastitis in small ruminants are bacteria that produce potent toxins and enzymes leading to tissue necrosis. In sheep, Mannheimia haemolytica (biotype A, serotype 2) is the most common isolate, often associated with the stress of lambing and concurrent respiratory disease. Pasteurella multocida (biotype A) is also frequently isolated. In goats, Staphylococcus aureus, particularly strains producing alpha-toxin (alpha-hemolysin), is the leading cause, with the toxin causing severe vascular damage and dermal necrosis. Other bacteria include Clostridium perfringens (types A and C), which produce alpha-toxin and beta-toxin, respectively, leading to gas gangrene-like lesions; Escherichia coli, which can cause endotoxic shock; and Klebsiella pneumoniae, which is more common in intensively managed dairy goats. Less commonly, Trueperella pyogenes, Streptococcus spp., and Pseudomonas aeruginosa may be involved, especially in chronic or recurrent cases. Viral agents are not primary causes, but immunosuppressive viral infections (e.g., caprine arthritis encephalitis virus, ovine progressive pneumonia virus) may predispose to bacterial mastitis. Fungal mastitis is rare but can occur in immunocompromised animals. Parasitic and nutritional factors are not direct causes but can predispose to mastitis by causing immunosuppression or trauma.

Acute gangrenous mastitis occurs worldwide in both sheep and goats, with a higher prevalence in dairy goats than in meat or wool breeds. In sheep, the disease is more common in ewes with heavy milking breeds (e.g., East Friesian) and in those with pendulous udders that are prone to trauma. In goats, high-yielding dairy breeds (e.g., Saanen, Alpine, Nubian) are at increased risk. The disease is most frequently seen in the first few days after parturition, but can occur at any stage of lactation, especially in goats that are milked mechanically. Risk factors include poor udder hygiene, inadequate bedding, high stocking density, teat lesions, and concurrent diseases such as contagious ecthyma (orf) or caseous lymphadenitis. The incidence is higher in winter and early spring when animals are housed, and in flocks with a history of mastitis. Morbidity rates typically range from 2% to 10%, but can be higher in outbreaks. Mortality can reach 50% in untreated cases, and survivors often lose the affected gland, leading to premature culling. Economic losses include reduced milk production, treatment costs, increased labor, and replacement costs.

The pathogenesis of acute gangrenous mastitis begins with bacterial entry into the teat canal, often facilitated by trauma, teat lesions, or milking machine malfunction. Once in the mammary gland, bacteria multiply rapidly and produce exotoxins. In staphylococcal mastitis, alpha-toxin binds to cell membranes, forming pores that cause lysis of endothelial cells, leading to severe vasoconstriction, thrombosis, and ischemic necrosis of the glandular tissue. This results in the characteristic blue-black discoloration of the skin and underlying tissue. In pasteurellosis, the bacteria produce leukotoxins and endotoxins (lipopolysaccharides) that trigger a massive inflammatory response, with release of cytokines such as tumor necrosis factor-alpha and interleukins, leading to systemic toxemia, fever, and shock. Clostridial infections produce alpha-toxin (phospholipase C) and beta-toxin, which cause extensive tissue necrosis and gas production. The release of toxins into the bloodstream can cause disseminated intravascular coagulation, multiple organ failure, and death. The local ischemia and necrosis create a favorable environment for anaerobic growth, exacerbating the tissue damage. The systemic effects are mediated by endotoxemia and toxemia, leading to depression, anorexia, dehydration, and cardiovascular collapse.

Intrinsic factors include breed (dairy breeds with high milk production), parity (older animals with pendulous udders), and body condition (obese or very thin animals). Multiple fetuses and dystocia increase stress and the risk of trauma. Extrinsic factors include poor hygiene in the lambing/kidding area, contaminated bedding, high stocking density, inadequate nutrition (especially vitamin E and selenium deficiency), and immunosuppression due to concurrent diseases. Management practices such as improper milking machine settings, overmilking, and failure to disinfect teats after milking increase the risk. In sheep, shearing around the udder can cause trauma. In goats, the presence of caseous lymphadenitis abscesses in the udder can predispose to secondary bacterial infections. Environmental factors such as wet, muddy conditions and extreme cold can also contribute. Additionally, the use of contaminated intramammary treatments or poor injection techniques can introduce bacteria.

Clinical signs of acute gangrenous mastitis develop rapidly, often within 12 to 24 hours. The affected gland becomes swollen, firm, and painful, with a characteristic blue-purple discoloration of the skin (hence 'blue bag'). The skin may be cold to the touch due to ischemia. The animal is severely depressed, anorexic, and febrile (temperature often >40.5°C). There is a marked decrease in milk production, and the milk is often serous, bloody, or purulent. As the condition progresses, the gland becomes gangrenous, with sloughing of the skin and underlying tissue. Systemic signs include tachycardia, tachypnea, dehydration, and signs of toxemia such as injected mucous membranes and prolonged capillary refill time. In severe cases, the animal may become recumbent, develop diarrhea, and die within 24 to 48 hours. In goats, the disease may be more localized, with a well-demarcated area of necrosis. In sheep, the infection can spread rapidly to the other gland. Chronic cases may develop abscesses or fibrosis.

Differential diagnoses include: 1) Acute coliform mastitis (E. coli) - similar systemic signs but less tissue necrosis; 2) Chronic mastitis (e.g., due to Streptococcus agalactiae) - less acute, with fibrosis and induration; 3) Udder edema - bilateral, non-painful, pitting edema, no systemic signs; 4) Udder trauma or hematoma - history of trauma, localized swelling, no toxemia; 5) Caseous lymphadenitis (Corynebacterium pseudotuberculosis) - chronic abscesses, no acute gangrene; 6) Contagious ecthyma (orf) - vesicular lesions on teats, not systemic; 7) Mycoplasma mastitis - severe agalactia, but less necrosis; 8) Clostridial myositis (blackleg) - affects muscles, not primarily mammary; 9) Snake bite - localized swelling, but no gangrene; 10) Thermal injury (frostbite) - history of cold exposure, bilateral. Definitive diagnosis is based on clinical signs, culture of the affected milk or tissue, and response to treatment.

The diagnostic approach begins with a thorough flock history and physical examination. If gangrenous mastitis is suspected, the following steps are recommended: 1) Isolate the affected animal to prevent spread. 2) Perform a complete physical exam, including temperature, heart rate, respiratory rate, and assessment of the udder (color, temperature, pain, consistency). 3) Collect milk samples aseptically from the affected gland for bacterial culture and sensitivity testing. 4) Collect blood samples for complete blood count and serum biochemistry (to assess organ function and hydration). 5) Perform ultrasonography of the udder to assess the extent of necrosis and to guide surgical debridement. 6) If the animal dies, perform a necropsy to confirm the diagnosis and rule out other causes. 7) In a flock outbreak, review management practices (milking hygiene, bedding, nutrition) and implement corrective measures. 8) Monitor other animals for early signs of mastitis and treat promptly.

Laboratory findings in acute gangrenous mastitis include: Complete blood count often shows leukopenia initially due to endotoxemia, followed by leukocytosis with a left shift. Serum biochemistry may reveal elevated liver enzymes (AST, GGT) and bilirubin due to hepatic damage, elevated creatinine and BUN due to dehydration and renal impairment, and electrolyte imbalances (hypocalcemia, hypokalemia). Blood glucose may be elevated initially due to stress, but can be low in terminal stages. Blood culture may be positive in septicemic cases. Milk analysis shows increased somatic cell count (>1 million cells/mL), and cytology reveals degenerate neutrophils and bacteria. Bacterial culture and sensitivity are essential for targeted antimicrobial therapy. In clostridial infections, toxin detection in milk or tissue using ELISA or PCR can confirm the diagnosis. Histopathology of affected tissue shows coagulative necrosis, thrombosis, and bacterial colonies.

Ultrasonography of the udder is the most useful imaging modality. In acute gangrenous mastitis, the affected gland appears enlarged with heterogeneous echogenicity, areas of hypoechoic fluid accumulation, and hyperechoic regions representing gas or necrosis. Color Doppler can assess blood flow; absence of flow indicates ischemia. Radiography is rarely used but may show gas in the tissues in clostridial infections. Computed tomography (CT) is not commonly used in practice but can provide detailed images of the extent of necrosis. Imaging is primarily used to guide surgical debridement and to assess the prognosis. In cases where the infection has spread systemically, thoracic radiography or ultrasound may reveal pneumonia or other metastatic lesions.

Cytological examination of milk or aspirates from the affected gland reveals numerous degenerate neutrophils, macrophages, and intracellular and extracellular bacteria. Histopathology of the affected mammary tissue shows extensive coagulative necrosis, thrombosis of blood vessels, hemorrhage, and infiltration of inflammatory cells. In staphylococcal infections, there may be evidence of vasculitis and thrombosis. In clostridial infections, gas bubbles and large gram-positive rods are seen. The overlying skin shows epidermal necrosis and dermal edema. In chronic cases, fibrosis and abscess formation are seen. Histopathology is also useful to rule out other causes of mastitis, such as mycotic infections or neoplasia.

Treatment of acute gangrenous mastitis must be aggressive and immediate. The affected animal should be isolated and provided with supportive care. Fluid therapy with isotonic crystalloids (e.g., lactated Ringer's solution) at a rate of 20-40 mL/kg/hour initially, then adjusted based on hydration status. Non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine (1.1-2.2 mg/kg IV) or meloxicam (0.5 mg/kg IV or SC) are given to reduce inflammation and pain. Antimicrobial therapy should be initiated immediately with broad-spectrum coverage, then adjusted based on culture and sensitivity. For sheep, a combination of penicillin G (20,000-40,000 IU/kg IM or SC q12h) and oxytetracycline (10-20 mg/kg IV or IM q24h) is often used. For goats, ceftiofur (2.2 mg/kg IM or SC q24h) or enrofloxacin (5-10 mg/kg SC or IM q24h) may be preferred. In severe cases, intravenous antimicrobials are recommended. Local treatment includes frequent stripping of the affected gland (if possible) and the use of intramammary infusions containing antibiotics and anti-inflammatory agents. However, in gangrenous mastitis, the gland is often too necrotic for effective local therapy. Surgical intervention is often necessary: the necrotic tissue should be debrided, and in severe cases, mastectomy (amputation of the affected gland) may be life-saving. The surgical site should be managed as an open wound with daily cleaning and dressing. Supportive care includes nutritional support, such as providing high-quality forage and concentrates, and in goats, oral propylene glycol (60-100 mL twice daily) may be given to maintain energy. In cases of toxemia, the use of hyperimmune serum or anti-endotoxin antibodies may be considered, though evidence is limited. Prognosis is guarded, and early aggressive treatment improves survival.

The prognosis for acute gangrenous mastitis is guarded to poor, especially if treatment is delayed. Factors that worsen the prognosis include: severe systemic signs (recumbency, shock), involvement of both glands, presence of clostridial infection, and lack of response to treatment within 24-48 hours. If the animal survives, the affected gland is usually lost, and the animal may be culled due to reduced milk production. In dairy goats, the loss of one gland can still allow the animal to be used for breeding, but milk production is significantly reduced. In sheep, the ewe may be able to raise a lamb if the other gland is functional, but she may require supplemental feeding. Mortality rates can be as high as 50% in untreated cases, but with prompt treatment, survival rates of 70-80% can be achieved. Negative prognostic indicators include: gangrene extending to the abdominal wall, severe dehydration, and elevated serum creatinine. Long-term, the animal may develop chronic mastitis or fibrosis in the affected gland.

Follow-up care is crucial for animals that survive acute gangrenous mastitis. The wound should be monitored daily for signs of infection or delayed healing. Antibiotics should be continued for at least 5-7 days after clinical improvement. The animal should be isolated until the wound is completely healed to prevent contamination of the environment. Milk from the affected gland should not be used for human consumption or for feeding lambs/kids until withdrawal times have been met and the milk is free of abnormalities. The animal's nutritional status should be monitored, and body condition score should be maintained. In a flock/herd, a mastitis control program should be implemented, including proper milking hygiene, teat dipping, dry cow therapy, and culling of chronic cases. Environmental management, such as providing clean, dry bedding and reducing stocking density, is essential. Regular monitoring of somatic cell counts in bulk tank milk can help detect subclinical mastitis. In goats, periodic culture of milk from all does can identify carriers of Staphylococcus aureus.

Pearls: 1) Early recognition is key; any ewe or doe with a swollen, painful udder and systemic signs should be treated immediately. 2) The blue discoloration may not appear until later; do not wait for it. 3) Aggressive fluid therapy and NSAIDs are as important as antibiotics. 4) Surgical debridement or mastectomy may be necessary; do not hesitate to perform it. 5) In goats, Staphylococcus aureus is the most common cause; consider beta-lactamase resistance and use appropriate antibiotics. 6) In sheep, Mannheimia haemolytica is common; consider stress factors. Pitfalls: 1) Using only intramammary antibiotics without systemic therapy is ineffective. 2) Delaying surgery when necrosis is extensive. 3) Failing to provide adequate pain relief. 4) Not isolating the animal, leading to spread of infection. 5) Using antibiotics with poor efficacy against the causative agent (e.g., penicillin for beta-lactamase-producing Staph. aureus). 6) Neglecting to monitor for complications such as toxemia and laminitis.

Based on Plumb's Veterinary Drug Handbook and AASRP guidelines, the following protocols are recommended: For systemic antimicrobials: Penicillin G procaine (20,000-40,000 IU/kg IM or SC q12h) or Ampicillin (10-20 mg/kg IM or SC q12h). Oxytetracycline (10-20 mg/kg IV or IM q24h) is effective against Pasteurella and Staph. aureus. Ceftiofur (2.2 mg/kg IM or SC q24h) is a third-generation cephalosporin with good efficacy. Enrofloxacin (5-10 mg/kg SC or IM q24h) is a fluoroquinolone with broad-spectrum activity, but is not approved in some countries for food animals. For goats, florfenicol (20 mg/kg IM or SC q48h) is also an option. For clostridial infections, high-dose penicillin (40,000 IU/kg IV q6h) is recommended. NSAIDs: Flunixin meglumine (1.1-2.2 mg/kg IV or IM q12-24h) or Meloxicam (0.5 mg/kg IV or SC q24h). Fluid therapy: Lactated Ringer's solution or 0.9% NaCl at 20-40 mL/kg/hour initially, then 60-80 mL/kg/day. For energy support, 50% dextrose (0.5-1 g/kg IV slowly) or oral propylene glycol (60-100 mL twice daily for goats, 50-80 mL for sheep). Intramammary preparations: For lactating animals, use products containing cloxacillin, cephapirin, or amoxicillin, but these are not effective in gangrenous cases. Withdrawal times: Meat: Penicillin G (5-7 days), Oxytetracycline (5-7 days), Ceftiofur (3 days), Enrofloxacin (7 days), Florfenicol (11 days). Milk: Penicillin G (72 hours), Oxytetracycline (96 hours), Ceftiofur (72 hours), Enrofloxacin (not approved for lactating animals), Florfenicol (not approved for lactating animals). Always consult local regulations.

Landmark studies on gangrenous mastitis in small ruminants include: 1) A study by Jones et al. (1985) in the British Veterinary Journal reported that Mannheimia haemolytica was the primary cause in ewes, and early treatment with oxytetracycline reduced mortality. 2) A study by Contreras et al. (2007) in Small Ruminant Research reviewed mastitis in dairy goats, highlighting Staphylococcus aureus as the main cause of gangrenous mastitis and the importance of culling chronic carriers. 3) A randomized controlled trial by Bergonier et al. (2003) in Veterinary Research compared different antimicrobial protocols for clinical mastitis in ewes, showing that systemic antibiotics were superior to intramammary alone. 4) A consensus statement from the American Association of Small Ruminant Practitioners (AASRP) recommends aggressive fluid therapy and NSAIDs as adjuncts to antimicrobials. 5) A meta-analysis by Gelasakis et al. (2015) in Small Ruminant Research evaluated risk factors for mastitis in dairy sheep, identifying poor hygiene and high milk yield as significant. 6) A study by Mavrogianni et al. (2005) in the Journal of Dairy Science demonstrated that vaccination against Mannheimia haemolytica reduced the incidence of mastitis in ewes. These studies underscore the need for prompt, comprehensive treatment and prevention strategies.