Posthatch growth of the digestive system in wild and domesticated ducks.

1. Our study was designed to test the hypothesis that domestication and artificial selection have influenced the posthatch growth and functioning of the gastrointestinal (GI) tract of ducks. The mass and length of the GI tract organs, the growth of intestinal villi, the intestinal surface area and the activities of brush border digestive enzymes were measured in a commercial strain of Pekin duck and its wild ancestor, the mallard (Anas platyrhynchos), at regular intervals between hatch and 16 weeks of age. 2. The growth of the digestive organs, with respect to body mass, was described using allometry. Allometric mass exponents were then used to calculate body 'mass-corrected', or 'relative' organ masses, relative surface areas and relative enzyme activities. There were appreciable differences between data presented on a mass-specific (g/kg) and a mass-corrected (g/kg(b)) basis, which highlighted the importance of correcting for the complete effects of body mass when comparing the growth and function of the digestive system between strains. 3. While the process of domestication has induced major changes in the absolute characteristics of the GI tract, it has failed to have the same effect on the relative characteristics. During the first 2 weeks posthatch, the relative masses of the majority of digestive organs, and the GI tract as a whole, were the same in both strains. During weeks 3 to 5, domesticated ducks maintained higher absolute growth rates of the body and the GI tract, with the support of relatively smaller digestive organs. The relative masses of the small intestine and the GI tract as a whole were 45 and 66% higher respectively in mallards than in Pekin ducks during this period. 4. Domesticated ducks had elevated digestive enzyme activity and a greater absorptive surface area than mallards throughout development, both in absolute and relative terms. This appears to compensate for the failure of the relative masses of digestive organs in domesticated ducks to accompany the increased body mass and growth rate. 5. At 5 weeks posthatch, the absolute mass of the small intestine in domesticated ducks declined by 38%. There is no obvious explanation for this decline because the masses of other digestive organs, daily feed intake and body mass continued to rise.