Or HaChaim on Exodus 9:6/אור החיים על שמות ט׳:ו׳

1 .כל מקנה מצרים, all the cattle of Egypt. This refers to the cattle the Egyptians had not brought indoors, this is why the words "in the field" are missing here.

2וממקנה בני ישראל, and of the cattle of the Israelites none died. They owned cattle going back to the time Jacob had come to Egypt. On the other hand, they may have acquired cattle from the money they received from the Egyptians when they sold them water during the plague of blood. It is even possible that some smart Egyptians "sold" their cattle to the Jews before the onset of the plague [much as we sell chametz to the Gentiles before Passover Ed.] so as to escape the plague and not interfere with their cattle's grazing outdoors. The Torah then would tell us that such "sales" did not protect such cattle; only the cattle which were truly Jewish-owned survived the plague without having been indoors. We ought to understand what the verse tells us: 1) "All the cattle of the Egyptians as well as some of the cattle "owned" by the Jews died;" the Torah added the extra letter מ in the line וממקנה בני ישראל to tell us about these so-called Jewish-owned cattle which died. The letter מ applied only to part of the cattle and not to part of the sheep and goats. To sum up: animals owned outright by Jews did not die; animals owned by Jews in name only, died.