The natural immune system of young cloned pigs does not appear to fight diseases as effectively as the immune system of non-cloned pigs, according to studies by scientists with the US Department of Agriculture and the University of Missouri.

Animal physiologist Jeff Carroll of the USDA's Agricultural Research Service collaborated with scientists from the University of Missouri-Columbia to study how the immune systems of cloned pigs differ from those of non-cloned pigs.

In their experiments, the scientists gave a naturally occurring toxin called lipopolysaccharide to seven young, cloned pigs and 11 genetically similar, non-cloned pigs. Although the non-cloned pigs' immune response was adequate, the cloned pigs' immune system did not produce sufficient quantities of natural proteins called cytokines, which fight infections.

Cloned pigs, as well as cloned cows, have been known to have a higher-than-normal death rate around the time of birth. Many die from bacterial infections.

As newborns, both the cloned and non-cloned pigs received some disease protection through their consumption of colostrum, a natural substance passed to a newborn pig via its mother's milk. The colostrum helps protect the young animal until its own immune system begins to function.

The cloned pigs are being used only for research purposes, and are not part of the food supply.