When horses undergo intense exercise, such as during racing or fast training workouts, they can sometimes suffer from exercise-induced pulmonary hemorrhage (EIPH). EIPH occurs when the blood pressure in the lungs rises to such high levels that capillaries in the lungs rupture and bleed. This results in blood from the lungs entering the airways. Horses may then cough up or swallow blood. If a horse bleeds due to EIPH, veterinarians often prescribe a course of antibiotics as a preventative measure against infection. There are a few reasons for this:
The blood acts as a growth medium for bacteria. Blood contains proteins and nutrients that allow bacteria to thrive and multiply quickly. Bacteria are naturally present in the horse's respiratory system, so the introduction of blood can lead to bacterial proliferation.
Bleeding damage provides an entry point for bacteria. Ruptured capillaries create openings where bacteria can invade lung tissue more easily and cause infection.
Blood accumulation impairs immune defenses. Blood in the airways can interfere with the respiratory tract's ability to trap and remove inhaled contaminants through mucociliary clearance. This allows bacteria to take hold more readily.
Strenuous exercise stresses the immune system. The high exertion of racing and fast training can temporarily suppress the horse's immune function, making it harder for the body to fight off infection itself.
In short, vets often prescribe antibiotics prophylactically after episodes of EIPH because the presence of blood allows bacterial growth, undermines mechanical and immunological defenses, and increases infection risk. Quick antibiotic treatment helps prevent respiratory issues like pneumonia from taking hold during this vulnerable period. Careful monitoring and follow-up care are still important however to ensure the horse recovers fully.