Grapes have high amounts of phenolic compounds, which can modulate the gut activity
as well as modify the structure and function of the gastrointestinal tract. The microbiological
activity of avoparcin, grape pomace concentrate, and grape seed extract was evaluated
in an in vitro study. An in vivo experiment was also conducted to study the effect
of the inclusion of grape pomace concentrate and grape seed extract in the diet of
broiler chicks on performance, intestinal microflora (by cultured and terminal restriction
fragment length polymorphism methodology), and gut morphology at 21 d of age. Dietary
treatments included an antibiotic-free diet (CON), a positive control (AVP; 50 mg/kg
of avoparcin), and antibiotic-free diets containing grape pomace concentrate (GPC;
60 g/kg) or grape seed extract (GSE; 7.2 g/kg). Performance was not affected by dietary
treatment except in the case of birds fed the GSE diet, which showed decreased weight
gain. In the ileal content, birds fed CON and GSE diets had the highest populations
of Lactobacillus. Compared with the CON diet, the AVP, GPC, and GSE diets increased
the populations of Enterococcus and decreased the counts of Clostridium in the ileal
content. In the cecal digesta, birds fed GPC and GSE diets had higher populations
of Escherichia coli, Lactobacillus, Enterococcus, and Clostridium than birds in any
other treatment group. Animals fed GPC and GSE diets showed a higher biodiversity
degree than those fed control diets. The frequency of detection of several potential
phenol-degrading bacteria as well as unidentified and uncultured organisms was increased
in animals fed GPC and GSE diets. Birds fed the CON diet had longer villi and deeper
crypt depth than birds in any other treatment group. The highest villi height:crypt
depth ratio corresponded to birds fed GPC and AVP diets and the lowest to those fed
CON and GSE diets. In conclusion, dietary polyphenol-rich grape products modify the
gut morphology and intestinal microflora and increase the biodiversity degree of intestinal
bacteria in broiler chicks.