Invited review: Aspects of gastrointestinal tract growth and maturation in the pre- and postweaning period of pigs

The growth and development of the gastrointestinal tract (GIT) of the young pig, both before and after parturition, is critical for the animal's future growth and development, efficiency of feed conversion to body depots, and, ultimately, its survival. The perinatal development of the GIT encompasses a prenatal phase, a neonatal phase, and the postweaning phase, which is associated with the adaptation of the GIT to utilize solid feed after the piglet is weaned. The consumption of colostrum, initially, and then milk after birth provides nutrients and compounds for piglets that are critically important as stimuli and substrates to the GIT that in turn evoke a suite of anatomical, immunological, biochemical, physiological, and regulatory processes that advance the overall maturity of the GIT. However, at weaning the combined influence of the various stressors imposed causes a hiatus in the growth and development of the GIT, such that the newly weaned pig endures a growth check while exposing it to a greater disease and health risk. Low and variable feed intake is a major outcome of the weaning process, but nevertheless, there are numerous nutritional/management interventions producers can implement in an attempt to overcome this major issue. This review summarizes some major aspects of, and influences on, GIT growth, development, and maturation in the pre- and postweaning period of pigs, demonstrating that postnatal influences occur in utero and that evolution of the GIT continues to occur after weaning.