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Since most foals are born in the late winter or early spring, the dry hot weather that their first summer brings can be very stressful as they begin losing the protection of the maternal immunities they received from their dam.
The foal's immune system is very immature and has not reached an adequate level of protection against pneumonia and other diseases. Young foals tend to play and over-exert themselves, often kicking up dirt and dust that they inhale. It is the inhalation of the bacteria Rhodococcus equi that most often leads to severe pneumonia in foals.
This bacteria breeds in the manure of horses and other grazing animals during the warm months and is found in the soil of most horse environments.
Although symptoms of pneumonia in foals may be noticed immediately, they often do not lead to a diagnosis until the disease is well-established and the foal has already developed lesions in the lungs, liver, lymph glands, and intestines. Fortunately, not all foals exposed to R equi bacteria fall ill with pneumonia, and some that do develop a mild form of the disease and recover quickly with minimal treatment.
- Increased respiration and pulse rate
- Difficulty breathing
- Loss of appetite
- Nostril flaring and reluctance to move
- Nasal discharge with crusting at the nostrils
- Abdominal breathing
- Reluctance to lie down because of breathing difficulty
Actuallly, foal pneumonia has several causes, stemming from bacteria, viruses, and parasites. The leading cause is the Rhodococcus equi bacteria, which breeds in herbivore manure.
Viral pneumonia is the result of the Equine herpes virus 2. Usually, foals are born free of this infection, but virtually all acquire the infection during the first months of life. Pneumonia is a common sign of the virus.
Parasitic pneumonias are not common in horses, but Parascaris equorum is a common parasite, with a life cycle involving migration through the lungs, which can cause signs of respiratory disease. Parasitic pneumonia is often seen in foals with a poor deworming history, coughing, nasal discharge, and a poor response to antimicrobials.
So far, there are no commercial Rhodococcus equi vaccines available. One technique that has been effective with horses on properties where there have been yearly sicknesses and deaths from R equi pneumonia is the use of hyperimmune plasma.
Dr. Madigan and his colleagues at UC Davis in California discovered that plasma obtained from adult donor horses that had been vaccinated several times with a preparation containing R equi bacteria that had been killed, prevented R equi pneumonia in foals which were given a transfusion of one liter of plasma when they were between one and thirty days old.
More information about this method of prevention is needed and will be added when it becomes available.
Foal management practices that include environmental and preventative care should be in place to prevent development of foal pneumonia.
Dirt floors in stalls, breeding farms with large numbers of mares and foals, and a population of transient mares and foals create risks for development of pneumonia caused by R equi. To minimize risks, precautions need to be taken by installing appropriate stall floors and minimizing exposure to the R equi organism.
To date, the best treatment is antimicrobial therapy, which should be initiated without delay when symptoms appear. A course of penicillin antibiotic should be started as soon as possible and can be changed when necessary, based on results of cultures and tests.
A veterinarian should be consulted as soon as foal pneumonia is suspected. Only a qualified professional can make an accurate diagnosis by using culture and sensitivity tests and then can prescribe appropriate treatment.
The foal should be kept in warm, dry quarters. Dehydration often occurs and measures should be taken to ensure that the foal has plenty of fresh water available and is drinking an appropriate amount. Anti-inflammatory drugs will help reduce fever. If lung abscesses develop, prolonged treatment is necessary.
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