<font color=blue>Round baled hay loses a lot of the nutrients from being exposed to the elements.</font color=blue>
I don't think it's the shape of the bale that matters; just that round bales are frequently stored outside in the weather, while square bales are usually stored inside. And for anyone who doesn't know, some of the round balers can be bought to use the twine that is perhaps the most common, or they can be bought to use the "wrap" (plastic wrap that Cowboydoc mentioned). I have one neighbor who's primary business is hay; buys a new John Deere baler every two years, and uses the plastic wrap exclusively; says that wrap makes each bale cost approximately $1 more to put up than using twine. Another neighbor, whom I spent a lot of time helping bale hay, has a Gehl baler he bought to use the twine, and has always wished he'd bought it set up for the wrap instead, but thinks it's too expensive to convert it.
Bird