"Let My people go, that they may serve Me. For if you refuse to let them go, and still hold them, behold, the hand of the Lord will be on your cattle in the field, on the horses, on the donkeys, on the camels, on the oxen, and on the sheep--a very severe pestilence. And the LORD will make a difference between the livestock of Israel and the livestock of Egypt. So nothing shall die of all that belongs to the children of Israel" (Exo. 9:1-4).
Pharaoh was also told that the next day was the set time for this plague. God delivered as promised. "All the livestock of Egypt died [i.e., all the livestock in the fields per verse 3]; but of the livestock of the children of Israel, not one died" (9:6). Horses and cattle were highly valued in Egypt and considered sacred. The Egyptians worshiped the god Apis, who was represented as a bull. The Apis bull supposedly had the power of prophecy and was the living image of the god Ptah. Pharaoh was certainly angry about this plague, but it wasn't as troubling to him personally as some of the earlier ones. He could deal with dead animals easier than with frogs or flies, which were uncomfortable for him personally. Pharaoh specifically made it a point to check to see if Moses' words were correct regarding Israel's animals. He found that they were exactly right. Not a single Israelite animal perished from the plague! Pharaoh was perhaps trying to ascertain if all the inhabitants of the land (both Egyptian and Israelite) were suffering from "bad luck" or if there really was a deity out there (i.e., Jehovah) punishing him for not releasing the Israelites. For God to be able to announce both the time and precisely which animals the plague would (and would not) affect clearly shows His power and dominance over the gods of Egypt. Even after all this, Pharaoh still foolishly refuses to budge.
"So the LORD said to Moses and Aaron, 'Take for yourselves handfuls of ashes from a furnace, and let Moses scatter it toward the heavens in the sight of Pharaoh. And it will become fine dust in all the land of Egypt, and it will cause boils that break out in sores on man and beast throughout all the land of Egypt.' Then they took ashes from the furnace and stood before Pharaoh, and Moses scattered them toward heaven. And they caused boils that break out in sores on man and beast. And the magicians could not stand before Moses because of the boils, for the boils were on the magicians and on all the Egyptians. But the LORD hardened the heart of Pharaoh; and he did not heed them, just as the LORD had spoken to Moses" (9:8-12).
Insects were a nuisance and boils were painful. God will not let up on the hard-hearted Pharaoh! Moses scattered ashes toward the sky, as if into the faces of the Egyptian deities. The boils broke out on the Egyptian people and animals, even the magicians (who could not protect themselves or Pharaoh)! The LORD is showing His power over the Egyptian gods and nature and over Pharaoh and his leaders. This particular plague would have been a rebuke to Serapsis (the god of healing), Imhotep (the god of medicine), and Thoth (the god of intelligence and medical learning). Where are these gods when the Egyptians need them?