Hello Hope, it could also mean that animals from "all" of the different "kinds" of livestock that belonged to the Egyptians were killed
(as @JIMINZ has already pointed out above .. see post #12), and/or that the deaths occurred among the flocks and herds who were living in the fields/not in shelters as your Study Bible's footnotes say.
Whatever the case may be, this cannot be a contradiction, and that for all kinds of reasons
(not the least of which would be the fact that this is all taken from the same Chapter in the Exodus). For what it's worth, I have yet to find a true contradiction in the Bible
(though our atheist friends, along with their father, of course, would have us believe otherwise).
God bless you!
--David