Although inherited forms of neutrophil dysfunction have not been described in the horse, neutrophil function test (phagocytosis and oxidative burst activity) is indicated when clinical signs include recurrent dermatitis or cutaneous abscesses caused by opportunistic or encapsulate bacteria (Serratia ssp., Streptococcus ssp.), or fungi (Candida spp). Although healthy foals are born with competent neutrophil function, newborn foals fighting severe infection demonstrate a transient decrease in phagocytosis and oxidative burst activity. The clinician should be aware of such possibility, although testing for its presence is unnecessary.

Pelger-Huet anomaly (PHA) of neutrophils has been identified in the horse (Dr. Melinda Wilkerson, Kansas State University; Julia Bevilaqua Felippe, Cornell University, unpublished data). Pelger-Huët cell neutrophilic function is normal, i.e. they phagocytose and kill microorganisms, and no clinical signs of immunodeficiency are observed. Therefore, the diagnosis is incidental, during the evaluation of blood smears. Pelger-Huët cells present dumbbell-shaped bilobed nuclei, and a reduced number of nuclear segments.