The terms "neonatal septicemia," "bacteremia," and "sepsis" have all been used to describe newborn calves with a systemic infection. Bacteremia is the presence of bacteria in the bloodstream, detected by blood culture. Septicemia refers to a systemic state associated with the persistence of pathogenic microorganisms and/or their toxins in the blood. Sepsis is a combination of an infection (or suspected infection) and a systemic inflammatory response. The systemic inflammatory response syndrome is the host inflammatory cascade that begins when the host defense system fails either to recognize or to clear the infection.
Four criteria are considered to establish a diagnosis of septicemia: abnormal core temperature, heart rate abnormality (tachycardia or bradycardia), tachypnea, and leukocyte count abnormality (leucopenia or leukocytosis). Septic shock is an exacerbation that results in hypotension and/or hypoperfusion. In multiple organ dysfunction syndrome, a primary pathologic condition affects a critically ill patient so severely that it causes the failure of multiple organs.
In North America, neonatal septicemia typically affects dairy calves < 2 weeks old. It is due to a failure of passive transfer. Most affected calves develop systemic infections after exposure to bacteria such as Escherichia coli or Salmonella. Neonatal septicemia can be sporadic or epidemic if poor management practices result in a high prevalence of passive-transfer failure, or if calves are exposed to high numbers of bacterial pathogens. Without treatment, focal infections in growth plates, joints, or meninges may develop.
Etiology of Neonatal Septicemia in Bovine Neonates
E coli has long been assumed to be the main microbial agent causing neonatal septicemia in calves. In fact, historically, "colisepticemia" was the term used to describe the clinical signs. Various researchers have shown the diversity of bacteria that may be involved. Although E coli remains the most commonly found bacterium, it is not the only one. Salmonella, Campylobacter, Klebsiella, and different Staphylococcus spp can be involved as well.
Most bacteria that cause septicemia derive their effect from one or more of the following virulence factors: adhesion capacity, serum resistance, aerobactin production, and toxin synthesis.
Risk Factors of Neonatal Septicemia in Bovine Neonates
Newborn calves are particularly at risk of septicemia because they depend on colostral antibodies for the passive transfer of immunity. Calves born into a heavily contaminated environment may be colonized by infectious pathogens before normal flora can be established. Septicemia may be associated with a primary site of infection, such as an umbilical infection. Dairy calves may be infected via contaminated colostrum. Infection may also be acquired in utero through the placenta, or during parturition. In the hours immediately after birth, nonspecific pinocytosis in the gut may allow bacteria to enter the systemic circulation.
In older calves with enteritis (bacterial, viral, or parasitic), fissures in the intestinal wall may allow bacteria to enter the bloodstream. Other points of entry for bacteria (eg, Salmonella) include the nasal mucosa, nasopharynx, and oropharynx. In calves 2–3 weeks old, a primary site of infection (umbilicus, septic joint, lungs [via pneumonia], or CNS [via meningitis]) can be either the source of septicemia or be the result of a previous episode of septicemia.
Infected calves excrete a large number of bacteria in their urine. Their nasal secretions and saliva also transmit bacteria. A common source of virulent isolates could contribute to the incidence of the disease on a particular farm or in a particular area of a farm.
Pathophysiology of Neonatal Septicemia in Bovine Neonates
The immune response, in combination with the reticuloendothelial system, prevents sepsis from developing as the result of an opportunistic or pathogenic invasion. However, the inflammatory cascade that is initiated as part of that response involves highly toxic mediators and could lead to systemic inflammatory response syndrome and multiple organ dysfunction syndrome. Increased endothelial permeability, myocardial depression, and intermediary metabolism disruption are notable recognized complications that eventually result in hypovolemia, hypotension, and respiratory failure.
Clinical Findings of Neonatal Septicemia in Bovine Neonates
Classic septicemia is described as a condition that affects newborn calves 2–5 days old. The progression is rapid and usually fatal. Very early in the disease, the clinical signs are nonspecific. Mild depression to coma and lack of suckling ability is commonly observed. Abnormal rectal temperature (fever or hypothermia) is possible but not always present. Sustained tachycardia and tachypnea are observed in advanced cases. Hyperemia of the mucous membranes, scleral injection, and petechiation of the mucous membranes could be observed. Hypotension and complications of poor cardiac output (slow capillary refill, diminished peripheral pulse, cold extremities, and decreased urine output) become prominent. Dehydration is usually present. Diarrhea is common in advanced cases.
A less acute form of septicemia occurs in calves 7–28 days old with localized infection (arthritis, growth plate infection, hypopyon, meningitis, pneumonia). Partial failure of passive transfer or exposure to less virulent bacteria could explained the mild clinical signs and more chronic evolution.
Diagnosis of Neonatal Septicemia in Bovine Neonates
Early diagnosis: clinical scoring system
Definitive diagnosis: blood culture
Definitive diagnosis of septicemia can be difficult. In most situations, treatment with antimicrobials should be initiated on the basis of a presumptive diagnosis. Definitive diagnosis is based on a positive blood culture. Many factors may interfere with bacterial isolation from a blood culture, so a negative result must be interpreted with caution. Cultures of other body fluids (joint, cerebrospinal, peritoneal, or pleural) or abscesses may provide useful results.
Hematologic changes vary with the severity of the disease. Abnormal neutrophil count (neutrophilia or neutropenia) or abnormal neutrophil morphology (bands, myelocytes, metamyelocytes) are frequently observed. Vacuolation, toxic granulations, and Döhle bodies may be observed in neutrophils. The fibrinogen concentration is frequently elevated. Thrombocytopenia may be present in severe cases. Hypoglycemia or, less often, hyperglycemia may be observed.
As the disease progresses, increased tissue lactate production and decreased hepatic clearance result in lactic acidosis. Organ function is compromised in severe cases, and laboratory results reflect the insufficiency. Some calves develop respiratory disease (respiratory distress syndrome Acute Respiratory Distress Syndrome of Feedlot Cattle An acute respiratory distress syndrome has been described in feedlot cattle with clinical signs and pathologic findings of an atypical interstitial pneumonia. The syndrome occurs sporadically... read more ) or even embolic pneumonia, leading to hypoxemia and/or hypoventilation. Imaging of the chest (radiography and ultrasonography) can be a valuable aspect of patient assessment. Calves with septicemia have low serum protein concentrations because of low globulin concentrations.
Scoring systems have been developed to facilitate early diagnosis of septicemia. Predictors used by these scoring systems include the following: age, focal infection, attitude and suckling ability, hydration, diarrhea, heart and respiratory rates, glucose, creatinine, hematologic changes, and serum proteins.
For More Information
Garcia J, Pempek J, Hengy M, Hinds A, Diaz-Campos D, Habing G. Prevalence and predictors of bacteremia in dairy calves with diarrhea. J Dairy Sci. 2022;105:1,807-817.
Fecteau G, Paré J, Van Metre DC, et al. Use of a clinical sepsis score for predicting bacteremia in neonatal dairy calves on a calf rearing farm. Can Vet J. 1997 Feb;38(2):101-104. PMID: 9028593; PMCID: PMC1576546.
Treatment of Neonatal Septicemia in Bovine Neonates
Administration of antimicrobials to control infection
Administration of anti-inflammatories
Nutritional, respiratory, perfusion support as needed
Neonatal septicemia is a critical condition. Mortality is high. Treatment aims to control the infection, attenuate the negative effect of the inflammatory response, and support the patient.
It is important to begin treatment as soon as possible. Antimicrobials should be administered without delay to decrease the bacterial load; IV administration is preferred. The choice of antimicrobial depends, in part, on geographic location (ie, the drugs permitted for use in food-producing animals vary in different countries); farm-specific bacterial resistance patterns should also be considered. The drug must cover the spectrum of gram-negative and gram-positive bacteria. Once the pathogen has been identified and the susceptibility pattern determined, the most appropriate antimicrobial can be selected.
Either steroids or NSAIDs should be considered in the treatment plan. NSAIDs are often preferred. Possible adverse effects of aggressive NSAID treatment include abomasal ulcers and renal toxicosis. To minimize potential adverse effects, NSAIDs should be continued only as long as they are considered essential for survival.
Supportive care includes administration of IV fluids, plasma transfusion, oral or parenteral nutrition, and oxygen administration. Secondary problems (eg, hypoglycemia and/or metabolic acidosis) identified on laboratory analysis should be corrected appropriately. IV fluids should be administered when possible. Dextrose (2.5%–5%) combined with physiological saline (0.9%) should be administered at a rate of at least 50 mL/kg every 24 hours. Transfusion of plasma (1–2 L) may be useful. Hypertonic bicarbonate (5.4%) can be administered with IV fluids to correct metabolic acidosis if the base deficit exceeds 10 mmol/L.
Patients that refuse to nurse or are unable to do so should be tube-fed to ensure milk intake equal to at least 10% of body weight every 24 hours (a strict minimum of 15%–20% would be ideal). Several feedings per day (3–5) may prevent abdominal distention. If the gastrointestinal system becomes overfilled by milk and ileus develops, parenteral nutrition should be considered. Because most animals will continue to nurse or tolerate tube-feeding up to 5% of their body weight, the parenteral nutrition does not need to be total. Partial parenteral nutrition is less expensive and easier to manage. Enteral feeding (suckling or tube-feeding) provides nutrients to maintain gastrointestinal system function. Calves with hypoxia without hypercapnia may benefit from intranasal oxygen insufflation (5–10 L/hour). In cases of hypoventilation, calves require mechanical ventilation.
Supportive nursing care of the patient should be provided. Its importance should be communicated to the client or caregiver. Optimal ambient temperature and ventilation are crucial. To prevent ulceration of the skin, especially around joints, a heavy, thick layer of straw bedding should be provided. Straw is recommended instead of wood shavings, because of its insulating properties and because the surface tends to stay dry, permitting feces or urine to drop to the bottom of the enclosure.
Prevention of Neonatal Septicemia in Bovine Neonates
The aim of prevention is to control the risk factors listed above. Adequate colostrum management is essential. The environment and management practices on the farm should be carefully inspected. Clusters of septicemia should be investigated, as they could be a result of preventable risk factors (eg, feeding heavily contaminated colostrum).
Calves are at risk to develop septicemia, most often due to failure of passive transfer.
Mortality from neonatal septicemia is high: early recognition and intervention are critical.
Involvement of multiple organ systems should be anticipated; assessment of the whole patient is required.
Critical care management is required for calves with septicemia, including antimicrobials, nutritional support and respiratory and circulatory augmentation.