Your three-month-old foal has made it through the birthing process and the vulnerable neonatal period and now seems to be carefree--your little one just has to grow up to fulfill his destiny as a performance horse. Although tonight he was a little quiet in the stall, he was eating well and seemed to have just a little yellow discharge from his nostrils--nothing to worry about, right? The next morning, the foal obviously is not well; he is standing in the corner struggling for every breath . . . .

Pneumonia, as most people know, means disease involving the lungs. The actual definition is inflammation of the lungs, which could be due to a multitude of factors, bacterial pneumonia, viral pneumonia, etc. But what does pneumonia look like in the foal? What are the warning signs and/or clues that your foal is in the early stages of pneumonia? When do you call your veterinarian? In this article, we will discuss pneumonia in the young foal and will focus on the obvious and sometimes subtle signs of pneumonia. We will concentrate on the most common bacterial causes of pneumonia.

How Common Is Pneumonia?

Pneumonia was found to be the major cause of illness and death in foals from one to six months of age, according to a Texas A&M study. A report out of Canada found that 75% of foals on Thoroughbred breeding farms in that area developed pneumonia. All of this sounds scary, but many foals develop pneumonia. We never see any signs of the disease, then it resolves on its own in that foal--often to be transmitted to other foals on the farm without us knowing. That's the danger with pneumonia in foals; certain bacteria can cause huge outbreaks on farms affecting the majority of the foal population. So, in a nutshell, pneumonia is a common disease in foals, and unfortunately sometimes a fatal one.

What Does Pneumonia Look Like?

Foals which are in the early stages of pneumonia might show no obvious signs of disease. The more subtle signs of pneumonia include an increased respiratory rate (tachypnea) and/or increased respiratory effort. Foals with more advanced pneumonia might have a fever, nasal discharge (purulent material or pus coming from both nostrils), and/or coughing. Unfortunately, these signs that are obvious to us are not always present, even in very sick foals. Nasal discharge might or might not be present as the discharge often is swallowed. Foals with severe pneumonia will have marked respiratory effort--the foal might look like he is breathing as if he had just finished a race. Foals which are this sick often are misinterpreted as having colic because they are in such a state of distress.

Other signs of illness (not just pneumonia) in foals can include lethargy (not as active or playful as normal). Sick foals also might not eat or nurse as much as they should. You might notice that the foal's head is covered in milk--this is from the foal's making weak attempts at nursing. A sick foal will go to the udder and bump the mare's bag, stimulating milk letdown, then just stand under the udder while the milk streams all over his face. Monitoring the mare's udder also is a tell tale sign of foal well-being. If the mare's udder is engorged, and occasionally streaming milk, the foal is not nursing. A healthy foal will nurse from the mare six to seven times an hour, keeping the udder small.

The best way to monitor your foal is to watch for any signs of coughing or nasal discharge--these are the hallmark signs of pneumonia. You also should become familiar with the normal resting respiratory rate and character of breathing for your foals. Neonates (foals less than two weeks of age) often have resting respiratory rates of 30 breaths per minute. Older foals (one to six months) often have respiratory rates much lower at 12-24 bpm. These rates can change if the weather is very hot and humid or if they have just been running or playing. But, if your foal's respiratory rate is higher than it should be for no reason, have your veterinarian examine the foal.

Being able to detect subtle changes in your foal's breathing requires skill. Watch for flaring of the nostrils and increased movement of the rib cage when breathing. If your foal is displaying these signs while resting, there is a problem. So, keep a close eye on your foal, and if you notice an increased respiratory rate or even if you are suspicious, then have your veterinarian examine your foal.

What About Defense?

Horses have several defense mechanisms in their lungs to help prevent infection. The horses' normal defense mechanisms of the lung include the mucociliary clearance system, which is a system by which tiny cilia move mucus, bacteria, and foreign material (particles of dirt, shavings, hay, etc.) out of the lung and up the trachea. The particles usually are swallowed. Other defense mechanisms include special killer cells that engulf bacteria and other foreign debris that reach the deep lung tissue, and two different types of immune systems (cellular and humoral) to protect the lungs from infection.

What Causes Pneumonia?

The development of pneumonia can be complex in the foal as it can be caused by multiple organisms--viruses, bacteria, and even internal parasites, either working alone or together to wreak havoc in the lung. The immune status of the foal--especially in the neonate--also factors in on the development of pneumonia. In young foals (less than one month of age) in particular, veterinarians are very concerned about the degree of immunity the foal has acquired from its dam's colostrum. If the foal did not receive adequate colostrum (failure of passive transfer) it results in an inadequate supply of immunoglobulins, and the foal is very susceptible to infection. Remember, foals have no other defense mechanisms at this age to fight infection. These foals can develop pneumonia from an infection that originally occurred in another part of their body, such as diarrhea or an umbilical infection.

Older foals will develop pneumonia usually not from the bloodstream (hematogenously), but as a result of inhaling the bacteria. The bacteria are inhaled quite inconspicuously and implant themselves in the respiratory tract within the lungs. If there are low numbers of bacteria inhaled, the foal's body can destroy the bacteria and head off infection. If, however, there are an overwhelming number of bacteria inhaled or if the foal's defense mechanisms are down from stress, concurrent or recent viral infection or poor ventilation, the bacteria can take over and lead to pneumonia.

The most common organisms which cause pneumonia in the foal are bacteria. Bacterial pneumonia generally is caused by the same bacteria that normally inhabits the upper respiratory tract (pharynx, larynx, nasal passages), and gastrointestinal tract of horses, such as Streptococcus sp. especially S. zooepidemicus. Bacteria usually found in the gastrointestinal tract such as Salmonella species, Klebsiella species, and E. coli are much more commonly implicated in causing pneumonia in neonatal foals--when the pneumonia is a result of bacteremia (bacteria which gain access to the blood stream and then spread throughout the body), leading to sepsis (generalized infection) and subsequently, pneumonia.

However, most pneumonia in foals occurs between the ages of four weeks and six months. The bacteria are thought to be inhaled, often attached to dust particles. The bacteria then attach to the respiratory tract and, if the defenses of the respiratory system are down or the sheer numbers of bacteria inhaled are great, the bacteria will multiply and eventually cause disease.

What About Rhodococcus?

Another bacterium that causes pneumonia in foals (one to six months of age) is Rhodococcus equi, commonly just referred to as Rhodococcus. This bacterium, which lives in the soil, can cause disease in the lungs as well as in other areas of the foal's body, such as in the gastrointestinal tract, where it can lead to colitis (diarrhea) or affect the musculoskeletal system, where it can cause septic joints. At the American Association of Equine Practitioners meeting in 1997, several talks were dedicated to the discussion of Rhodococcus as outbreaks of this disease had led to infection rates as high as 80%(morbidity) on large farms. Rhodococcus is not a simple infection that cures itself. Treatment can be intensive, and overwhelming infection is not uncommon. It can lead to death or a recommendation of euthanasia due to a hopeless prognosis for recovery.

This particular bacterium leads to pneumonia and abscesses within the lungs or other areas of the body in foals which are less than six months of age. The problem with Rhodococcus, is that it is often not recognized until the disease is well advanced and then it is very difficult to treat. Rhodococcus typically only affects foals. There are only a few reports of the disease occurring in adults, and these horses either were immunocompromised or had other simultaneous diseases that made them susceptible. Rhodococcus also has been reported to cause disease in humans who are immunocompromised, such as people infected with the HIV virus.

How Do Foals Become Infected?

The Rhodococcus bacterium is thought to gain access to the lungs from being inhaled with dust particles. The bacteria live in the soil, and when the ground becomes dusty in the summer months from overcrowding or lack of rainfall, they easily gain entrance to the foal's lungs. The bacteria also enjoy the warm temperatures of summer, so they can multiply tremendously during this time, leading to exposure and possible infection for more and more foals. The bacteria are endemic on some farms and become a chronic problem every summer.

Preventing Rhodococcus Infection

Steve Giguere, DVM, from the Ontario Veterinary College, discussed at the AAEP several methods for controlling Rhodococcus on farms known to have the disease.

Because the environment is known to be a large contributing factor to the development of the disease, he recommends housing foals in well-ventilated, dust-free areas. If you have dusty paddocks or aisleways, both can be hosed or sprinkled with water to help keep the dust under control. Overcrowding also is a contributing factor to this disease. Housing sick foals in the next stall or same paddock is playing Russian roulette with the spread of this disease--it only will be a matter of time. If you have a farm where foals from another farm are coming in with their mares to be bred, keep these foals separate from your foals. Mixing foals from different farms is a sure way to spread respiratory viruses and bacteria.

Rotation of pastures also is an ideal way to prevent dust formation and therefore inhalation of the bacteria. This helps decrease the amount or concentration of bacteria to which a foal might be exposed and, thus, decrease the chance that a foal will develop the disease.

Other Types Of Pneumonia

Bacteria also can be inhaled along with food particles. This is known as aspiration pneumonia. It is not as common as other types of pneumonia, but can occur if a foal or horse develops choke (esophageal obstruction). This also can occur if a foal has a cleft palate, which is a congenital defect by which there is a communication between the nasal passages and the soft palate. When the foal nurses, milk can travel from the palate into the nasal passages, then the milk can be inadvertently inhaled. Most of us have had that occasional bit of food or drink travel down the wrong pipe--a mouthful of food gets inhaled into the trachea or windpipe instead of being swallowed. This usually happens to me when I am eating my first meal of the day at 8 p.m., and I am too hungry to stop eating and breathe, then, boom! We hopefully just cough it back up and no big deal. When this happens over and over due to choke or other problems that allow for aspiration of food, the sheer number of bacteria eventually overwhelms the natural defense mechanisms of the lungs and in short order, the foal has pneumonia.

What About CID?

In combined immunodeficiency (CID), which is a hereditary disease usually seen only in purebred Arabians, the foal is born without the ability to develop a normal immune system. More specifically, the foal is unable to produce a type of white blood cell that helps fight off infection. So, the foal is usually born normal and healthy, but after six weeks or so, as the antibodies from the mother's colostrum begin to wane, the foal cannot fight off infection. Many of these foals develop life-threatening pneumonia and although we can use antibiotics to help kill the bacteria, without a functional immune system to take over where the maternal antibodies left off, the bacteria overwhelm the animal and pneumonia is often the result.

Diagnosing Pneumonia

If your foal is showing any of the clinical signs of pneumonia that were discussed, have your veterinarian examine the foal. Your veterinarian will perform a physical examination of the foal that will include listening to the lungs with the aid of the stethoscope. If the lungs are diseased, they will have abnormal sounds called crackles and/or wheezes. Or the lungs might be too quiet and not have normal breath sounds. To make an accurate diagnosis of pneumonia, a tracheal wash can be performed one of two ways. One way is to perform the "wash" from the underside of the horse's neck. The "wash" can be performed by placing a needle through the skin, then into the trachea and advancing a small plastic catheter deep into the trachea. A small amount of sterile water is injected into the trachea, then the water, along with mucus, phlegm, and hopefully bacteria, will be aspirated back into a syringe and evaluated under the microscope. The veterinarian will look for the type of cells present, such as bacteria and white blood cells. He or she will also look for food particles to determine if the animal is aspirating food.

The second way to perform a tracheal wash involves placing an endoscope (a small fiberoptic camera) into the horse's trachea. A long plastic catheter then can be advanced into the trachea through the endoscope and the sterile water can be injected into the trachea. The rest of the procedure is exactly the same. Regardless of the method, a tracheal wash allows the veterinarian to acquire a sample of material from the lungs that contains bacteria that will be grown in culture to determine what type of bacteria is causing the infection. Furthermore, the bacteria can be tested (called a sensitivity test) to see what antibiotics will be most effective to treat the infection. This procedure often is necessary for successful treatment of pneumonia.

Other diagnostics that are used to help evaluate the severity of pneumonia are ultrasound examinations and radiographic (X ray) studies of the chest. An ultrasound examination easily can be performed at the farm to help your veterinarian determine if there is fluid between the chest wall and the lung, which indicates pleuropneumonia. Using ultrasound, the veterinarian also can evaluate the health of the lung that is outermost in the chest. Radiographs of the chest are very useful in foals, as they can detect abscesses, such as seen with Rhodococcus infection, or deep lung disease that simple auscultation and ultrasound examinations cannot detect. Radiographs are difficult to obtain on the farm and your foal might need to be referred to a clinic for the X rays to be performed.

How Is Pneumonia Treated?

Once a diagnosis of pneumonia has been made, your veterinarian will place the foal on antibiotics to help fight the infection. The choice of antibiotics is dictated by the results of a culture and sensitivity. The foal will be placed on an antibiotic that has been shown to be effective in killing the bacteria that are present from the tracheal wash. This ensures that the treatment will be effective. If necessary, foals will be placed on intravenous antibiotics.

In very severe cases of pneumonia, the foal will need intensive care in a hospital. In these situations, an air-conditioned stall helps to decrease cooling demands on a young animal. In intensive care, oxygen also can be used. Nasal oxygen is often used in cases where the pneumonia is so advanced that a proper oxygen supply cannot be delivered from the diseased lungs. A small tube can be sutured into place within the foal's nostril and 100% oxygen supplied to help support the oxygen needs of the body until the lungs recover the ability to transport oxygen effectively from room air, which is only about 20% oxygen.

Other treatments used as an adjunct in treating foals with pneumonia include nebulization of saline with antibiotics and brochodilators. Nebulization is the process of aerosolizing saline into very small particles. The saline can be used to help loosen very sticky secretions, allowing the foal to have a more productive cough. The saline also is used as a carrier to transport antibiotics directly into the lung. Bronchodilators can be added to the solution to help open airways and allow for easier breathing. This can be performed several times a day. Nebulization also is used in adults for the treatment of pneumonia and heaves (chronic obstructive pulmonary disease). A commercial mask such as the Aeromask can be used or a more homemade one using half-gallon to gallon jugs can be used to help deliver the aerosol.

The best treatment however, is prevention. So, if you have had a problem with foal pneumonia on your farm, discuss with your veterinarian ways to prevent it in the future --such as keeping foals from different farms separated, so as not to expose them to new bacteria and/or viruses to which they have no immunity. Monitor closely for early signs of infection. Make sure the mares are well-vaccinated to help prevent viral respiratory outbreaks that can lead to bacterial pneumonia. Furthermore, if you have had a problem with Rhodococcus in particular, discuss with your veterinarian the possibility of administering intravenous hyperimmune plasma within the first week of life, to help foals develop resistance to this particular infection.

About the Author

Christina S. Cable, DVM, Dipl. ACVS

Christina S. Cable, DVM, Dipl. ACVS, owns Early Winter Equine in Lansing, New York. The practice focuses on primary care of mares and foals and performance horse problems.

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