Weanling pigs under sublethal concentrations of atmospheric carbon monoxide.

Atmospheric carbon monoxide at 200 ppm for 21 d had no adverse effect on any performance or behavioral characteristic measured in weanling pigs. The pigs tended to compensate for carboxyhemoglobin-induced reduction in oxygen-carrying capacity of their blood by increasing total hemoglobin concentration. Pigs exposed to carbon monoxide at 300 ppm had a 31% reduction in body-weight gain (.20 vs .29 kg/d) and a 20% reduction in feed conversion efficiency (gain/feed = .48 vs .60) at d 10. Over the 21-d exposure period, rate of gain was reduced by 21% (.31 vs .39 kg/d), feed conversion efficiency by 8% (.47 vs .51). There appeared to be a threshold concentration between 200 and 300 ppm above which atmospheric carbon monoxide reduced weanling pigs' performance.