Based on farm-level data from 744,500 head of pigs finished in confinement, the performance of pigs housed in tunnel-ventilation facilities was shown to be superior to that of pigs housed in natural-ventilation facilities, as measured by both daily feed consumption and feed conversion. This, in turn, resulted in higher average daily gain, a lower cull rate, and a lower feed cost per cwt of gain. The lower cost of gain, together with the reduced number of cull hogs and the extra 9.4 lb of market weight sold, are significant economic advantages that resulted in an estimated higher net return of $5.61 per pig for each group fed in tunnel housing
Iowa State University
Lally, Joseph and Edwards, William M., "Performance Differences between Natural-Ventilated and Tunnel-Ventilated Finishing Facilities" (2000). Swine Research Report, 1999. 22.