If there is one thing to say about using wood for calf pens it is: "Don't."
 
The porous surface of wood favors the penetration of parasite eggs and bacteria. This same surface is supremely difficult to clean. Thus, it becomes an effective way to pass pathogens on from one generation of calves to the next. Maybe you can remember years and years ago when we tried making hutches out of plywood panels - the first 4 or 5 turns of calves did pretty well and then it was steadily downhill from there in terms of calf health.
 
I was effective in getting this idea across to a client that built a new calf barn. He agreed to use wire pens rather than the wooden boxes that were part of the original plan.
 
Yesterday I visited the new barn. He proudly showed me how it was about 1/3 full of calves in neat rows of wire pens. One row was against the west wall, two more rows in the middle and one row against the east wall. 
 
So far so good. BUT, rather than buying enough wire pens to provide a fourth side for the pens along the wall, my client decided to save money and use the wooden sidewalls as the fourth side. How did I manage not to get across that all wood is undesirable?
 
Well, we had a discussion about this. He agreed to purchase some of the wire panels and for the remainder of the barn the calves will not be against the outside wooden walls.
 
As I completed the conversation it occurred to me to mention how far away from the walls the pens should be placed. He had not thought that far ahead. "What is your recommendation?" he asked. I told him to find out by trial and error.
 
Using his wire panels (recall they come with various size openings), place one 3 to 4 inches from the wall. Watch calves - can they lick the wall? No, then that distance is okay. Yes, then the pens need to be moved farther away.