A recent disagreement about the critical importance of gut flora to animal health led me to look for research into germ-free animals. GF animals have been available for research for about 50 years and initially they lived very short lives. The decrease in longevity was eventually traced to lack of critical enzymes in their diet. In order to remain GF their food was sterilized at high temperatures (essentially autoclaved) which caused the needed enzymes to break down. Once their dietary requirements were established an unexpected result emerged – GF animals live twice as long as controls receiving the same complete diet but not housed in sterile conditions.
Germ-free animals were obtained by cesarean section and maintained in special isolators; this allowed the investigator to raise them in an environment free from detectable viruses, bacteria, and other organisms. Two interesting observations were made about animals raised under germ-free conditions. First, the germ-free animals lived almost twice as long as their conventionally maintained counterparts, and second, the major causes of death were different in the two groups. Infection often caused death in conventional animals, but intestinal atonia frequently killed germ-free animals.
This got me thinking about evolution vs. design. The animals raised germ-free could not have evolved in the natural world without exposure to bacteria but they could have been designed for GF life. The fact that they live twice as long in a GF environment when eating a diet that is nutritionally complete except for being sterile seems to be favorable evidence that animals were created in and for a germ-free world.
My experience with rabbits, who often die of intestinal atonia when their diet isn’t perfect, leads me to suspect the frequent early cause of death in GF animals is still related to diet rather than lack of gut flora. Regardless they still live twice as long without bacteria (including gut flora) in them or their environment.