Toxic changes in the neutrophils in the peripheral blood smear appear due to accelerated production of neutrophils in response to severe inflammation or bacterial sepsis both in humans and animals. Most of the changes in toxic neutrophils appear due to asynchronous maturation between the nucleus and cytoplasm and is manifested as cytoplasmic vacuolation, cytoplasmic basophilia and presence of Dhole's bodies.

In equines it may be species characteristic that more primary granules are retained in the toxic neutrophils which take up the stain and are evident as more prominent toxic granules as compared to other species of animals and humans.

I would agree that horses do have more noticeable toxic change, but are you also comparing with non-toxic neutrophils from the same species? Normal foals will often have quite prominent granules that look similar to toxic change.

You should contact Prof. Didier Serteyn (registered on RG), on my behalf: he is a specialist in this field.

Best regards

Robert