Round bales are a cheap way to buy hay for stock when the grass dries off in winter or if you're keeping them in the yards. Round bales without round bale holders don't last more than 24 hours with our cattle! They tend to pull the whole thing apart and then lie down in it, poo in it and refuse to eat the rest. It makes a very expensive pile of mulch! With a good round bale holder, most of the hay will be eaten and only the stalks are discarded, but the holders are expensive to buy, around $400 in our area.
Before we owned a round bale holder (and after making a few expensive piles of mulch) we made a quick and cheap version using three cattle panels arranged in a triangle around the bale. Farmer Pete made one of the panels with wider rung spacing so the cattle could poke their heads through. This worked quite well, as a triangle is very strong and the cattle couldn't push it over, but it wasn't ideal for them to access the hay (and we needed the panels for our yard).
Later, when we were very busy and in need of a round bale holder, we bought the simple one pictured below. It is made from three pipe hoops, pipe uprights and mesh at the bottom to stop the hay from spilling out. It works very well, but with the new property we needed a second round bale holder and didn't want to pay for something that we could make, now that we had more time to work on it.
The difficulty with fabricating a round bale holder is bending the pipe into a circle, as this requires expensive bending equipment that we don't have access to. Farmer Pete decided to make it as a hexagon instead. We used a bit of geometry to work out the length of the sides and angles required to fit in a 3 foot bale and Farmer Pete made the cuts and easily bent the box section into shape. Then we did some really tricky geometry and made the holder at the right height for the bale with diagonal risers between each centre and corner. This stops the cattle putting their head in and tossing the hay around.