The effects of beak trimming on behaviour, morphology, and physiology of poultry: A systematic review

Abstract

Despite scientific and ethical concerns, beak trimming (beak treatment, or beak tipping) remains a routine procedure in the poultry sector. The perceived efficacy to reduce pecking-related injuries and mortality is the main reason for the common application of beak trimming. The aim of this systematic review was to identify the effects of beak trimming on the welfare of several commercially kept poultry species (chickens [ Gallus domesticus ], turkeys [ Meleagris gallopavo domesticus ], ducks [ Cairina moschata; Anas platyrhynchos ], quail [ Coturnix coturnix ], Guinea fowl [ Numida meleagris ] and pheasants [ Phasanius cholchicus ]). Following strict a priori in- and exclusion criteria, a total of 1,242 records were screened for eligibility, resulting in 175 studies included for data extraction. Risk of Bias was assessed based on the reporting of key quality indicators. Due to high heterogeneity of the 175 studies, a subset of 120 studies was analysed based on welfare-related outcomes in the domains of behaviour, morphology, physiology, and mortality and presented in effect-direction plots, showing beneficial, harmful or absent effects of beak trimming. Twenty-four studies investigated beak abnormalities, with 71% of those reporting morphological abnormalities and 25% altered sensory abilities. Of 49 studies, mortality decreased in trimmed birds in 51% and increased in 8%, while 41% reported no measurable impact. Physiological indicators of stress did not show clear patterns, but the procedure caused alterations in behaviour, such as a decrease in environmental pecking. The effects on preening and injurious pecking remain ambiguous. These results corroborate the inconsistent potential benefits of beak trimming and highlight the need for investigating underlying causes of severe feather pecking and refinement of techniques, not only in chickens.