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1033
From pre- to post-weaning: The adaptations of the gastrointestinal tract of the young calf
The ruminant gastrointestinal tract (GIT) faces the challenge of protecting the host from luminal contents and pathogens, while supporting the absorption and metabolism of nutrients for growth. The GIT of the calf in early-life undergoes some of the most rapid microbial and structural changes documented in nature and it is these adaptations in GIT function which make the young calf susceptible to gastrointestinal disease and disorders. Despite these challenges, the GIT of the calf has a certain degree of plasticity and can sense nutrient supply and respond to bioactive ingredients. For example, the pre-weaned calf can adapt to meal size by altering abomasal emptying as a means of controlling nutrient delivery to the intestine, thereby stabilizing blood metabolites. Despite this plasticity, research has historically focused on the transition during weaning and characterizing ruminal papillae development using microscopy. Through the use of molecular-based approaches we have recently shown that delaying the age of weaning and providing a step-down weaning protocol is associated with a more gradual shift in ruminal microbiota to a post-weaned state. In addition to ruminal adaptations during weaning, nutrient flow to the lower gut changes dramatically during weaning, coinciding with a wide array of structural and microbiological changes. A study examining structural and gene expression changes suggests that the lower gut of the dairy calf undergoes alterations that may reduce barrier function when solid feeds are consumed. Additionally, a recent in vivo calf study revealed that the weaning transition increases total gut permeability of the calf. Interestingly, some evidence suggests that the upper and lower gut are able to communicate with the forestomach, meaning that a nutrient can be sensed in the lower gut and cause subsequent adaptations in the forestomach. An improved understanding of how diet, microbiota, and functional ingredients interact to impact growth and barrier function of the intestinal tract would greatly benefit the industry. A mechanistic understanding of such adaptations would also aid in the formulation of specific management regimens and provision of functional ingredients required to support or enhance gut function in young calves.
Keywords: calf, gastrointestinal tract, weaning, functional nutrition