School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.
Poult Sci. 2018 Sep 1;97(9):3188-3206. doi: 10.3382/ps/pey191.
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.
鸡的消化系统简单、短且效率极高。在上消化道（GIT）或前肠中，特别是在饲料不是连续供应的情况下，饲料在嗉囊中被润湿，然后在腺胃和肌胃中分别进行化学和物理消化，为在 GIT 的远端部分——十二指肠、空肠、回肠中吸收营养做准备，而在盲肠和结肠中的吸收程度较低。过去的肉鸡饲养实践主要集中在获得高消化率的营养物质上，而在很大程度上没有考虑前肠的祖传目的。除了具有重要的消化功能外，丰富的细菌群落在嗉囊和肌胃中转化这些器官，成为防止病原体入侵 GIT 的屏障。然而，饲料在前肠中停留的时间——因此，这个肠道段的环境——是极其可变的，可以通过不同的饲养方式进行操纵，例如饲料结构和组成、喂养频率和/或光照制度。随着肉鸡在性能和健康方面的进一步发展，以及几十年来对远端 GIT 段的研究，是时候探索前肠如何为实现这些目标做出贡献了。本综述回顾了前肠的形态学、生理学和微生物学特征；探讨了该 GIT 部分作为饲料摄入调节剂的重要性；并讨论了如何通过光照制度和饲料结构等饲养和喂养方式来激活嗉囊和肌胃，从而提高性能和健康水平。最后，讨论了这些喂养方式与外源酶的相互作用，并提出了进一步研究的建议。
