Gastrointestinal Tract Morphometrics and Content of Commercial and Indigenous Chicken Breeds with Differing Ranging Profiles

SIMPLE SUMMARY: Differences in the range use by poultry exist on the individual or breed level, even if equal opportunity of outdoor access is provided. Birds reared with access to the pasture consume some of the material found outdoors, such as plants, insects, and stones. The frequency of outdoor range use may be associated with the ingested material and the development of the bird gut. Optimal gastrointestinal tract morphometrics or small intestine microstructure are important for nutrient absorption and essential for poultry to resist diseases and assure welfare. Development of the gastrointestinal tract and its content could furthermore retrospectively indicate the birds’ ranging profile. The aim of the current study was to compare gastrointestinal tract morphometrics, small intestine microstructure, as well as the amount of pasture-originating material and feed ingested by the birds differing in their ranging profile, separately for the slow-growing broiler hybrid Sasso and green-legged partridge, a Polish indigenous breed of chicken. We found that the contents of the crop and gizzard of the moderate-indoor green-legged partridges were different from the indoor- and outdoor-preferring ranging profiles. In Sasso, the development of the villi in terms of their height and area in outdoor-preferring birds was different from that observed in other ranging profiles. ABSTRACT: Optimal development of the gut is important for nutrient absorption and for poultry to resist diseases. The aim of the study was to compare gastrointestinal tract morphometrics, small intestine microstructure, as well as the amount of pasture matter and feed ingested by the birds with outdoor access presenting either an outdoor-preferring, moderate-outdoor or indoor-preferring ranging profile. Sixty non-beak trimmed birds per strain: broiler hybrid Sasso and Polish indigenous green-legged partridge were housed from week 5 to 10 in groups of 10, under conditions of EU organic meat chicken production. Pens with outdoor ranges were video recorded, to obtain frequencies of the birds’ range use. Statistical analysis was conducted applying generalized linear mixed models, applying the ranging profile as a fixed effect and pen as a random factor. The weight of the pasture matter in bird crops was the highest in moderate-outdoor profiled green-legged partridges, as compared to other ranging profiles (p = 0.04). In Sasso, villi in the small intestines were significantly higher in the outdoor-preferring compared to indoor-preferring profiled birds (p = 0.04), while their area was larger in the outdoor-preferring Sasso birds (p = 0.01). The level of development of the gastrointestinal tract and its content may be a potential indicator of the birds’ ranging profile and forage consumption.