Which of the following could be a possible cause of anemia?

Dehydration can indeed lead to a condition known as relative anemia. When an animal is dehydrated, the blood volume decreases due to the loss of fluids, which can concentrate the red blood cells within the available plasma. Although the total number of red blood cells does not actually decrease, the concentration appears lower, resembling anemia when evaluated.

In contrast, excessive hydration typically dilutes the blood, potentially leading to a condition known as dilutional anemia, but this situation is less common than dehydration-induced changes. A low platelet count pertains to thrombocytopenia, which influences clotting rather than red blood cell levels. Similarly, a high neutrophil count is usually a response to infection or inflammation and does not directly relate to red blood cell production or concentration. Thus, dehydration stands out as a direct influence on the apparent levels of red blood cells, making it a valid cause of anemia.