Three times in the Exodus account of God plaguing the Egyptians (Exodus 7-12), we read about the cattle of the Egyptians dying - specifically as part of the 5th, 7th, and 10th plagues:

Exodus 9:6

6 And the LORD did that thing on the morrow, and all the cattle of Egypt died: but of the cattle of the children of Israel died not one.

Exodus 9:19, 22, 25

19 Send therefore now, and gather thy cattle, and all that thou hast in the field; for upon every man and beast which shall be found in the field, and shall not be brought home, the hail shall come down upon them, and they shall die.
22 And the LORD said unto Moses, Stretch forth thine hand toward heaven, that there may be hail in all the land of Egypt, upon man, and upon beast, and upon every herb of the field, throughout the land of Egypt.
25 And the hail smote throughout all the land of Egypt all that was in the field, both man and beast; and the hail smote every herb of the field, and brake every tree of the field.

Exodus 12:29

29 And it came to pass, that at midnight the LORD smote all the firstborn in the land of Egypt, from the firstborn of Pharaoh that sat on his throne unto the firstborn of the captive that was in the dungeon; and all the firstborn of cattle.

So, how is it possible that the cattle of the Egyptians are dying or being smitten, when they "all" already died as the focus of the fifth plague?

One solution is found in the fact that when you read the account of the plagues, no precise time frame is given between each one. In fact, when reading the account, over and over again, Pharaoh agrees to let them go, but then won't. It would take time for that to happen - a few million people (Exodus 12:37) getting ready to leave, and then being prevented from doing so.

And, logically, if these plagues were happening immediately one after another, it's likely that the Egyptians would have ousted Pharaoh, or the Israelites, by force, as after a point, it would simply be too much. As time passes, and Pharaoh's heart has a chance to harden again, it gives him more plausible deniability, and puts some space between each of these disasters.

But really, not much time would be needed between the plagues at all. In an agrarian economy, if all of your cattle die, you don't just throw up your hands, and continue on with life. The animals you own are themselves a huge part of your life. So, you buy new ones, as fast as possible, from your neighbors - like the Israelites, for instance, who primarily lived in a part of Egypt called Goshen (Genesis 47:27, Exodus 9:26), whose cattle had been unharmed (Exodus 9:4-7, 9:26).

In any case, it's not hard for the Egyptians to have gotten more cattle after the 5th plague. And, they most likely only would have had to do so once for both the 7th and 10th plague to make sense, as there is no indication that all the cattle were wiped out completely again in the 7th plague, as they had been in the 5th plague.