Final answer:
Horses have the largest RBC diameter and the least anisocytosis among the given options.
Step-by-step explanation:
RBCs from horses have the largest diameter and the least anisocytosis among the options provided. Erythrocytes, commonly known as red blood cells, vary in size between different species. While the average diameter of a primate red blood cell is 7.5 µm and a dog's is 7.0 µm, it's even larger in horses. In comparison, a cat's RBC diameter is 5.9 µm and a sheep's is the smallest at 4.6 µm. Anisocytosis refers to a condition where there is a lot of variation in the size of erythrocytes within a single blood sample; therefore, horses having the least anisocytosis implies they have more uniform RBC sizes.