It will make a difference if those calves can be haltered. If they have never had a halter on before, then please have video camera ready. Sometimes a haltered calf just pulls backwards(if tied to something sturdy; ex: strong post or pole), but other times they may go crazy and more so if the other end of the rope isn't stationary(like human being). If you choose cattle panels, I would recommend getting combination panels. These are for cattle and hogs. The bottom 12"-16" have extra metal bars so small pigs can't excape. The reason for this suggestion is that when you transport animals, their manure makes their footing slippery and their hooves and legs will slid outward until they contact the edge or wall of the transport cage. You don't want their leg to be able to exit thru a normal size cattle panel hole and the animal may get injured. This reason also gives plywood an advantage. Yes, there will be manure, too. (nervous animals). Ask yourself; If I purchased plywood, could I use on a later project? OR If I purchased combination panels, could I use they elsewhere? My Dad has built some pasture gates out of cattle/combination panels over the years where he didn't need the strenght of steel tube gates. We did this using 2x4 framework around the perimeter of one side of the panel, then 4 vertical 2x4s on the other side. 2x4s at both vertical ends were bolted together. The two center, vertical 2x4s just bolted to the upper and lower, horizontal 2x4s dividing the center span equally.(wood was free from old barn that tornado took down). If those calves can't be haltered, then they have the chance to attempt to jump over whatever enclosure you built. This is where height is important. Do you have plans to move that cow in the future? OR when the calves grow, do you plan to move them? Consider building something that my be useful 6-9 months drove the road. Back on the farm, we only moved animals in a stock rack for the back of a pickup, or we called for the semi-tractor and trailer for larger quanities. Hope this helps.