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The absorptive surface of the small intestine is covered by a layer of mucus secreted by goblet cells. The secreted mucins and thickness of the adherent layer influence nutrient digestion and absorption processes as well as the functionality of the mucosa. In this study, methods for the analysis of mucin synthesis and dynamics in the chick small intestine are described. A fragment of chicken mucin cDNA was isolated and characterized; this fraction had 60% homology to human mucin MUC-5AC. The thickness of the mucus adherent layer and the relative amounts of mucin glycoprotein and mRNA were also examined in the small intestines of control and starved chicks. Relative amounts of intestinal mucin mRNA and protein increased in the duodenum and jejunum of starved chicks, and mucus adherent layer thickness decreased throughout the small intestine. In starved chicks, higher mRNA expression and protein concentrations with lower amounts of adherent mucus may be related to a higher rate of degradation of the mucus layer, a lower rate of mucus secretion, or an altered rate of mucin turnover. It thus appears that starvation alters mucus dynamics in the small intestine, and this may affect intestinal digestive function and defense. KEY WORDS: * chick * mucin * small intestine * starvation * mucus adherent layer