Final answer:
In ruminants, the predominant white blood cells are lymphocytes, which are a type of agranulocytes responsible for the adaptive immune response. Neutrophils are also important as they are the most prevalent in fighting bacterial infections, but they are not the predominant WBC in ruminants.
Step-by-step explanation:
The predominant white blood cell (WBC) in ruminants is the lymphocyte. In the context of leukocytes present in the bloodstream, granulocytes and agranulocytes play distinct roles in the immune response. Granulocytes, such as neutrophils, eosinophils, and basophils, are typically the first responders during injury or infection due to their phagocytic abilities and are characterized by a lobed nucleus and granular inclusions in the cytoplasm.
On the other hand, agranulocytes, which include lymphocytes and monocytes, are responsible for the adaptive immune response; lymphocytes, involving B and T cells, are particularly adept at recognizing and responding to specific pathogens. Monocytes differentiate into macrophages and dendritic cells, aiding in the removal of dead and damaged cells.
Neutrophils are phagocytic leukocytes found in the largest numbers in the bloodstream and are crucial in fighting bacterial infections. However, in the case of ruminants, lymphocytes are more abundant and thus the predominant white blood cells.