The pig is somewhat similar to humans in the function and relative size of many internal organs.
Antibodies can also better tolerate more neutral pH levels.
During passive immune transfer, antibodies are taken in with the colostrum and are then absorbed in the gut and transported to the circulatory system where they then protect the pig from harmful organisms. By about 5 weeks of age, stomach pH levels decrease to about 2. This degrades most proteins, including antibodies, and limits survival of most microbial species. Some beneficial bacteria, such as lactobacilli can tolerate or prefer acidic conditions. Thus they can colonize the stomach and the upper GI tract.