Growth and development of finishing pigs in bedded hoop and confinement buildings during summer and winter was evaluated using serial ultrasound measurements of backfat (BF) thickness, loin muscle (LM) area, and serial weighing. A summer trial (April through August 2000) and a winter trial (October 2000 through February 2001) were conducted. Forty-eight pigs from the hoop building and eight pigs from each of the six pens in the confinement building were randomly selected and weighed; ultrasound images were recorded every 14 d during the last 56 d of the finishing phase. Backfat accretion rates were greater for summer hoop pigs (SH) than summer confinement pigs (SC) at 80 kg to 90 (P < 0.05), but did not differ at 95 to 115 kg. In winter, BF accretion rates did not differ from 80 to 105 kg, but winter hoop pigs (WH) had less BF accretion than winter confinement pigs (WC) at 110 kg and 115 kg (P < 0.05). Loin muscle accretion rates did not differ at 80 and 85 kg or from 100 to 115 kg, but were less for SH than SC at 90 kg and at 95 kg (P < 0.001). WH had greater LM accretion rates than WC at 80 kg to 115 (P < 0.05). Bodyweight gain (BWG) did not differ between SH and SC from 80 to 95 kg and was greater for SH at 100 kg to 115 kg (P < 0.05). Bodyweight gain did not differ for WH and WC pigs from 100 to 115 kg, but was less for WH than WC at 80 kg to 95 kg (P < 0.05). These results indicate that performance of finishing pigs is dependent on the thermal environment, and that hoop-reared pigs (particularly in winter) may compensate for a lag in performance early in the finishing period with greater accretion rates of LM and BW and lower accretion rates of BF later in the finishing period.

Although overall pig performance in hoop and confinement buildings is similar, some differences in accretion rates for bodyweight, backfat, and loin muscle area occurred during the finishing period. These differences are probably due to seasonal variation in the thermal environment. Performance of pigs reared in hoop buildings may be compromised early in the finishing period by their inability to overcome the difference between temperature and thermoneutrality. However, it appears that hoop-reared pigs compensated for earlier lags in performance by increased BW gain and LM accretion, along with less BF deposition compared to pigs in confinement at the same BW. This study provides some evidence to justify feeding pigs in hoops to heavier weights. Research studying accretion rates of pigs at a wider range of bodyweights will be needed to better understand the effects of environment and building type on pig performance.