Sorry--
I'm coming in on this a little late. Here's part of a current article ( I can get you the source and the rest of it if anyone wants to PM me):
Pneumonia in Older Foals
As opposed to neonates that usually acquire pneumonia secondary to septicemia and spread of bacteria through the blood stream, older foals typically acquire pneumonia by inhalation of aerosolized or dust-borne pathogens. Although the viruses mentioned above and EHV-2 can cause pneumonia in older foals as well, the majority of cases of lower respiratory tract disease in older foals are caused by bacteria. The primary bacterial agents involved are, however, different than that isolated from neonates. Bacterial pneumonia in older foals is generally caused by opportunistic pathogens that are normal inhabitants of the equine upper respiratory tract or gastrointestinal tract or are environmental contaminants. Streptococcus equi subspecies zooepidemicus is the most common bacterial pathogen isolated. Rhodococcus equi occurs sporadically but is enzootic on some farms. Because R. equi constitutes the most devastating cause of pneumonia in older foals and is different from other forms of foal pneumonia in many regards, it is discussed in a separate article. Various other bacteria such as Actinobacillus, Pasteurella, and Klebsiella species, Bordetella bronchiseptica and E. coli can be isolated alone or in combination with S. zooepidemicus and/or R. equi.
The spectrum of clinical signs ranges from an otherwise normal appearing foal with occasional coughing and mild bilateral nasal discharge to one with severe cough, profuse nasal discharge, fever, anorexia and respiratory distress. Increased respiratory rate is a typical feature even in mildly affected foals. The respiratory rate is best assessed at rest during the cool part of the day. Resting respiratory rates greater than 40 per minutes at rest in an older foal or weanling is usually considered abnormal and deserves further evaluation.
Once pneumonia has been confirmed by a veterinarian, diagnostic evaluation should be directed at the entire herd because it is unlikely that a single foal will be affected. The need for diagnostic procedures is determined by the herd history, the number and the value of the foals, severity and duration of the clinical signs, treatment used and response to therapy. Foals with pneumonia may have an elevated white blood cell count and fibrinogen concentrations. Although there does not seem to be a high degree of correlation between the severity of the pneumonia and the magnitude of laboratory abnormalities, measurement of fibrinogen concentrations provides a useful means of monitoring response to therapy. Radiographs or ultrasonographic examination of the chest are useful means of evaluating the severity of lung damage and assessing response to therapy. Tracheobronchial aspiration with cytological examination and bacterial culture of the fluid recovered is the most definitive diagnostic procedure available. In the field setting it is not always practical or desirable to perform a tracheobronchial aspirate on all foals with pneumonia. The procedure should be considered on representative cases on farms where several foals are affected, in foals that are not responsive to conventional antimicrobial therapy or have atypical clinical signs, and in foals with markedly elevated fibrinogen or evidence of lung abscessation when R. equi is suspected. Whenever possible, antibiotic therapy should be discontinued at least 24h before performing a tracheobronchial aspirate. If an etiologic agent is cultured, several antibiotics can be tested for efficacy against the bacterial pathogen in vitro and help direct antimicrobial therapy.
Therapy consists of antibiotics to kill or inhibit growth of the causative microorganism(s). Since a high percentage of older foal pneumonia is due to penicillin-sensitive bacteria (this is not true for neonatal foals), penicillin is often used for initial therapy, pending culture results. Ceftiofur (Naxcel®) has a broad spectrum of activity which includes most of the etiologic agents of foal pneumonia, except R. equi. Trimethoprim-sulfonamide combination products are attractive because they also have a broad spectrum of activity which includes many of the causal agents of older foal pneumonia and they can be administered orally. Restricting exercise is important initially in more severe cases to limit respiratory demand. In milder cases and in those that are recovering, limited exercise may help promoting expectoration. Confinement in a cool, clean, dust-free, well-ventilated environment is required.
Most cases make a complete recovery if diagnosed early and treated appropriately. Treatment should be continued for at least 10 days, and much longer in serious cases. Clinical signs, white blood cell counts, measurement of fibrinogen concentrations, and imaging techniques (ultrasound, radiographs) can be used to assess effect of therapy.