Range usage or body weight has minor effect on the gastrointestinal passage rate of commercial free-range laying hen

Abstract

Free-range flocks are composed of hens that prefer to spend the majority of their time in sheds, "stayers", and hens that prefer to spend the majority of their time on the range, "rangers". While it was previously shown that rangers and stayers differ significantly in egg production, the rationale and underlying mechanism for the different performance remains unknown (Ruhnke and Sibanda, 2018). Range usage may contribute to improved digestive organ development such as the gizzard due to the positive effects of coarse fibre and grit stones leading to an increased grinding activity, and subsequently a decreased passage rate resulting in an increased exposure time of nutrients to digestive enzymes and overall increased nutrient digestibility (Amerah et al. 2009; Hetland et al. 2004). On the other hand, body weight may influence passage rate, due to a larger digestive tract convolute and subsequently larger quantities of enzyme secretion, and a larger intestinal absorption surface.