Years ago I used to tell people that having a pet that goes outside and inside is good for the immune system of kids. They tend to have fewer allergies. I never connected that to the concept that many human diseases come from livestock. For instance, influenza strains cross over to either chickens or pigs (swine flu). This study is interesting in that it suggests exposure to livestock can also boost the immune system.
It compares the fecal microbiota of Amish (kept cowsand/or horses) and Hutterite (just dogs) infants. The Hutterite children have 4-6 times the risk of asthma and allergies. The Amish households have higher levels and diversity of allergens, bacteria, and endotoxins. Ancestry beyond a couple hundred years of both groups are pretty similar. They primarily differ in environment they shape around themselves such as food consumption (grown vs purchased) which is potentially big confound.
Researchers delivered piglets via Cesarean-section so they had more sterile. The gave the piglets infant milk formula. And then they gave the piglets a fecal microbiota transplant from the infants. Later, they examined the DNA of the microbiota in the piglets to identify what was in the infant guts. Basically, the Amish microbiota resembles rural-types in previous studies and the Hutterite resembled urban-types. And the rural-types are better for properly training the immune system to lower the risk of allergies.
Really, this is more evidence of not being too scared about the presence of bacteria in our industrialized society. Exposure to a diversity of stuff means more will get into the gut. I recently learned in Gut that the immune system learns the bacteria it finds there and the appendix is where a selection are kept so that when diarrhea flushes the intestines, they can be repopulated with the bacteria we need. The rural lifestyle helps the infants get a better earlier diversity. And we as parents need to strike a balance between cleaning and overzealous cleaning. Too much kills eliminates the helpful bacteria.
Dhakal S, Wang L, Antony L, Rank J, Bernardo P, Ghimire S, Bondra K, Siems C, Lakshmanappa YS, Renu S, Hogshead B, Krakowka S, Kauffman M, Scaria J, LeJeune JT, Yu Z and Renukaradhya GJ (2019) “Amish (Rural) vs. non-Amish (Urban) Infant Fecal Microbiotas Are Highly Diverse and Their Transplantation Lead to Differences in Mucosal Immune Maturation in a Humanized Germfree Piglet Model.” Front. Immunol. 10:1509. doi: 10.3389/fimmu.2019.01509