Pneumonia and other lower respiratory tract infections in foals can result not only in substantial expense and inconvenience to the owner but can ultimately be fatal. Unfortunately, these conditions are very common, affecting as many as 30% percent of all horses in their first year of life. Why are these conditions so prevalent? Recent research has confirmed that foals are slightly deficient in their immune responses putting them at risk for infection by certain types of organisms. The failure to receive at birth adequate amounts of colostrum (the thin, yellow, milky fluid secreted by the mare's mammary glands carrying all of the antibodies that are needed for the first several weeks of life) further impairs a foal's immune responses and results in increased vulnerability to respiratory infection. Management influences, such as the stresses of weaning (discontinuation of breast feeding), sales preparation, transport and/or confinement in crowded or dusty conditions, can increase susceptibility.

When discussing foal pneumonia, it is useful to think in terms of two sets of circumstances — the neonate (foals younger than four weeks) and older foals (aged four or more weeks). In neonates, pneumonia is most often associated with a severe bacterial infection throughout the body but may also occur as a result of breathing milk into the lungs. A variety of bacteria can be responsible for this type of infection thereby requiring treatment with a broad spectrum (effective against a wide range of microorganisms) antibiotic therapy consisting of a single drug, such as Naxcel, or a combination of drugs, such as penicillin and amikacin. As a result of research done here at the Equine Medical Center, a nebulizer (spraying device) is often used to deliver antibiotics directly to the lungs, a method of delivery which appears to speed recovery in many neonates. In addition to antibiotic treatment, anti-inflammatory therapy using drugs such as Banamine may aid in controlling lung inflammation, improving lung function and increasing patient comfort. Unlike bacterial pneumonia, viral pneumonia occurs rarely in newborn foals, but is often fatal due to the severity of the inflammation in the lungs. There are no effective antiviral medications available, so treatment of these foals consists primarily of supportive care to maintain lung function and minimize stress. All neonates being treated for pneumonia must be closely monitored in order to ensure that the prescribed medications and treatments do not cause adverse side effects.

The second type of respiratory infections are those more commonly observed in older foals, from one to two months of age until weaning. Bacterial pneumonia in these foals is typically associated with a different population of bacteria than is seen in newborns, frequently involving the Streptococcus zooepidemicus and Rhodococcus equi organisms. A slightly different antibiotic regimen may be employed in these cases using oral antibiotics such as erythromycin and rifampin. However, other antibiotic regimens can be prescribed based upon the overall assessment of the attending veterinarian. Although still relatively rare in this group, viral pneumonias are more common in older foals. Viral infections cause pulmonary inflammation and can impair immunity thereby predisposing foals to subsequent bacterial infections in the lungs. Treatment in cases of suspected viral respiratory infections in older foals consists of anti-inflammatory therapy and supportive care.

The challenge for the attending veterinarian lies in determining whether the primary problem is viral or bacterial in nature. This determination is initially made by reviewing the patient's history, conducting a physical examination and analyzing the foal's blood. Some cases may require further diagnostic evaluation, such as x-rays, ultrasound examination and a tracheal wash (the collection of sterile secretions from the trachea). Unfortunately, it is very difficult to definitively diagnose viral pneumonia. Special tests such as viral isolation, polymerase chain reaction (PCR) testing for viral genetic material and the repeated testing of the foal's blood for increasing levels of antibodies to the virus are often required for a definitive diagnosis.

The most important component of supportive care for all foals affected by pneumonia is rest. Activity is likely to worsen their respiratory distress by exacerbating the inflammation within the lungs. Ill foals should never undergo stressful events such as weaning, transport or sales. Temperature control is also very important as foals with pneumonia have trouble regulating their body temperature and are vulnerable to hyperthermia, especially during the summer months. Environmental management is best achieved by turnout in a small grass paddock and/or by providing a stall with low dust bedding, such as pine shavings, rather than straw. Prolonged rest is often required in these cases, as inflammation remains in the lungs even after the offending infectious agent has been eliminated.

Pneumonia in foals is a very serious ailment and should be treated as an emergency condition requiring immediate medical attention. Symptoms of respiratory distress include increases in the rate of breathing, difficulty breathing or an inability to tolerate exercise. Due to their delicate nature, foals that are brought in to the Marion duPont Scott Equine Medical Center for critical care are always seen first by members of the hospital's internal medicine team. All of our internal medicine faculty are board certified by the American College of Veterinary Internal Medicine and specialize in the physiologic interaction among internal body systems in foals including respiratory disease. Owners may call 703/771-6800 to inquire about the neonatal and foal care services offered or to schedule a consultation.

Dr. McKenzie is an assistant professor of equine medicine at Virginia Tech's Marion duPont Scott Equine Medical Center. He can be reached at hmckenzi@vt.edu. To view his online profile, visit www.equinemedicalcenter.net. Virginia Tech's Marion duPont Scott Equine Medical Center is a premier full-service equine hospital located in Leesburg, Va., that offers advanced specialty care, 24-hour emergency treatment and diagnostic services for all ages and breeds of horses. One of three campuses that comprise the Virginia-Maryland Regional College of Veterinary Medicine, the center and its team of equine specialists are committed to providing exceptional treatment to patients, superior service to clients and cutting-edge research to the equine industry.