Infection with gastrointestinal pathogens is a major limitation to sustainable animal production. The need to reduce treatment with synthetic antimicrobials means that novel approaches to gut health, such as nutritional interventions that regulate or boost immune function, are of great interest. Phytonutrients are defined as plant compounds found in the diet that can have beneficial effects on health, and are becoming increasingly popular in livestock feed. Numerous studies have demonstrated the ability of different phytonutrients, such as polyphenols or essential oil components (EOC), to decrease inflammatory responses in the gut. Furthermore, recent work has demonstrated that some phytonutrients can increase specific immune responses elicited by gastrointestinal pathogens. In ruminants and swine, dietary polyphenols such as procyanidins can enhance the acquisition of cellular and humoral responses to mucosal-dwelling parasites, and ongoing work is investigating the relative contributions of the gut microbiome and direct interactions with immune cells in mediating these effects. EOC such as cinnamaldehyde have also been shown to enhance antibody responses to parasitic helminth infection in pigs, and the mechanisms of how cinnamaldehyde and similar compounds modify the host immune response are being explored. In vitro, cinnamaldehyde has well-documented anti-inflammatory effects but can also regulate a wide range of metabolic processes in different cellular models. Understanding how these effects on metabolic processes influence immune function has the potential to open up new avenues for nutritional modulation of the innate and adaptive immune system. A combination of in vitro systems, laboratory animal (mice) and large animal studies (pigs) are being currently undertaken to explore how cinnamaldehyde and related compounds influence local immune responses in the gut. This presentation will summarize the work being conducted to unravel these mechanistic interactions, as well as some perspectives on the use of defined phytonutrients to regulate immune function during key periods of animal growth.