Carbon Monoxide – Case in Point

by Kelley J. Donham DVM, DACVPM, professor and director
Iowa’s Center for Agricultural Safety & Health

A few years ago I was called by a local veterinarian whose pork producer client was having a problem in the farrowing house. Many of the pigs were stillborn, others were weak or small, and his weaning average was only two or three pigs per litter. I was asked to consult.


I reviewed what had been done, and was satisfied with the work he had done to rule out infectious causes, nutrition and toxins in the feed. I was really scratching my head on this case until I asked the producer if there were any differences in this condition during the year. He said the problem was only occurring in the winter. I also asked him how he was feeling. He told me that he was having unusual headaches. Bingo!! Do you now know what the problem might be, and what to do about it? I suspected carbon monoxide (CO) because of the seasonal nature of the problem, and the symptoms of headache in the producer. What I did not tell you is that the heaters for the newborn pigs were propane-fired brooder heaters (as seen in the picture). I took measurements of carbon monoxide concentrations and found about 400 parts per million around the heaters, and about 200 ppm at the nose of the sow. At about 200 ppm exposure, the sows are not clinically affected (although they may have headaches). However, the unborn pigs are much more susceptible to CO, and are receiving the equivalent of 800 ppm – enough to cause slow development, weak pigs, and small litters. The prevention of this situation is to switch to electric lamps and/or heat pads, or regular cleaning of the air intake screen on the heaters. The air intake screen plugs with dust easily, which causes the propane to burn incompletely, kicking out more CO. In terms of human health in this building with levels at 200 ppm, the effects would be subtle – headaches, slow reaction time and impaired judgment. However, if a pregnant woman was working in that building, there could be serious health problems to her unborn baby, such as low birth weight and slow mental development. The carbon monoxide exposure also could cause her to have a miscarriage.

Carbon monoxide results from incomplete combustion of carbon based fuels

Carbon monoxide is an odorless, colorless and tasteless gas that results from carbon-based fuels. When inhaled, it is easily transported into the blood. However, when the hemoglobin is already loaded with CO, it cannot carry oxygen. The unborn fetus, in both pigs and people, is much more susceptible to CO. For example, if the mother’s blood is 20 percent saturated with CO, the fetus will be 40 percent saturated – enough to cause serious health problems. Carbon monoxide is a very common agent of poisoning on farms and in homes and other businesses in general. CO poisoning is responsible for about 40,000 emergency room visits and about 800 deaths yearly. The following describes other cases of CO poisoning that I have investigated and represents most of the common hazards found on pork producing farms. I investigated a case similar to the one described above – in November again – but in this case all sows in the farrowing room suddenly aborted and two of 16 sows in the farrowing room were dead.