Marine macroalgal extracts to maintain gut homeostasis in the weaning piglet.

The mammalian gastrointestinal tract (GIT) is a dynamic environment, where a symbiotic relationship exists between the resident microbiota and the digestive and immune systems of the host. The development of the immune system begins in-utero and is further developed after the colonization of the GIT with microbiota during birth and postnatal life. The early establishment of this relationship is fundamental to the development and long-term maintenance of gut homeostasis. Regulatory mechanisms ensure an appropriate level of immune reactivity in the gut to accommodate the presence of beneficial and dietary microorganisms, whereas allowing effective immune responses to clear pathogens. However, unfavorable alterations in the composition of the microbiota, known as dysbiosis, have been implicated in many conditions including post-weaning diarrhea in pigs. Weaning is a major critical period in pig husbandry. It involves complex dietary, social, and environmental stresses that interfere with gut development. Post-weaning complications in piglets are characterized by a reduction in-feed intake and growth, atrophy of small intestine architecture, upregulation of intestinal inflammatory cytokines, alterations in GIT microflora, diarrhea, and heightened susceptibility to infection. These challenges have been controlled with in-feed prophylactic antibiotics and dietary minerals. However, these strategies are under scrutiny because of their role in promoting multidrug resistant bacteria and the accumulation of minerals in the environment, respectively. Therefore, significant efforts are being made to identify natural alternatives to support homeostasis in the piglet GIT, in particular during the weaning period. Chemodiversity in nature; including microorganisms, terrestrial plants, seaweeds, and marine organisms, offers a valuable source for novel bioactives. In this review, we discuss the advances in our understanding of the immune mechanisms by which the dynamic interplay of the intestinal microbiota and its host normally favors a homeostatic, symbiotic relationship, and how feeding macroalgal bioactives in both the maternal diet and the piglet diet, can be used to support this symbiotic relationship in times of challenge.