The foregut and its manipulation via feeding practices in the chicken

The digestive system of a chicken is simple, short, and extremely efficient. In the upper gastro-intestinal tract (GIT) or foregut, in particular when feed is not continuously available, moistening of feed occurs in the crop followed by chemical and physical digestion in the proventriculus and gizzard, respectively, as a preparation for nutrient absorption which occurs in the distal portions of the GIT-duodenum, jejunum, ileum, and to a lower extent in the ceca and colon. Broiler husbandry practices in the past have focused on achieving high intakes of readily digestible nutrients and largely failed to consider the ancestral purpose of the foregut. Besides holding important digestive functions, the rich bacterial communities in both the crop and the gizzard transform these organs in barriers preventing the invasion of the GIT by pathogens. However, the amount of time feed spends in the foregut-and therefore the environment in this gut segment-is extremely variable and can be manipulated by different feeding practices, such as feed structure and composition, frequency of feeding, and/or light regimes.With further progress in terms of performance and health of broiler chickens being sought, and following decades of research focusing on distal GIT segments, it is about time to explore how the foregut can contribute to achieve these goals. This review revisits morphological, physiological, and microbiological characteristics of the foregut; explores the importance of this GIT portion as feed intake regulator; and discusses how husbandry and feeding practices such as lighting regimes and feed structure may be adapted to activate the crop and the gizzard, which results in performance and health improvements. Finally, interactions of these feeding practices with exogenous enzymes are discussed and suggestions for further research are made.