Natural behaviours, their drivers and their implications for laying hen welfare

Abstract

Some believe that farm animals need to be kept in conditions that provide ‘natural’ aspects in the animal’s environment and, thus, provide the opportunity for the animals to perform their full ‘behavioural repertoire’. Captivity may restrict either behaviours that animals have instinctive, intrinsic propensities to perform whatever the environment or behaviours that are elicited by deficits in the animals’ environment. Behavioural restriction may also thwart general motivation to seek variety and/or avoid monotonous conditions. Appreciating whether an animal suffers if deprived of the opportunity to perform natural behaviour requires, first, an understanding of how the behaviour in question is elicited and controlled, the effects of early experience and genetics on the behaviour and the behaviour of the species in the wild, and, second, the behavioural, physiological and fitness effects of deprivation of the behaviour. Housing laying hens in conventional cages compromises their behavioural repertoire, such as nesting in a nest box, dust bathing, perching and foraging, and the present review focuses on the welfare implications if these natural behaviours are thwarted in modern poultry production. A floor space of <561 cm2/hen increases physiological stress, reduces egg production and increases mortality in laying hens. There is also evidence of behavioural restriction in terms of reduced wing stretching, leg stretching, tail wagging, locomotion, floor and object pecking and preening with floor space in the range of 542–750 cm2/hen. Preference and motivation research has indicated that laying hens value resources such as nest boxes for oviposition, substrates for foraging and dust bathing, and perches for roosting. However, there is no convincing evidence that deprivation of these resources results in physiological stress. Furthermore, apart from adverse effects of the absence of perches on bone strength, there is no evidence that deprivation of nest boxes, perches, and foraging and dust-bathing substrates results in reduction in fitness such as reduced egg production or health. Nevertheless, preference research has indicated that the opportunity to utilise these resources, particularly nest boxes, may elicit positive emotional states in laying hens. Therefore, it is important to understand both how motivated the animal is to choose an option or perform a behaviour as well as the consequences of depriving the animal of this opportunity.

Impacts of Rearing Enrichments on Pullets’ and Free-Range Hens’ Positive Behaviors across the Flock Cycle

“…The control hens overall showed less foraging relative to the structural hens, and they also exhibited the most plumage damage across time [5]. Foraging is proposed to function as both food searching as well as environmental exploration [11]. In this study, foraging was defined as scratching followed by pecking, but foraging in other studies has encompassed walking, pecking and scratching (e.g., [14]).…”

“…The perching/navigation structures and novel objects were not intended to specifically increase litter-related behaviors, although there were pecking strings provided as some of the novel objects within some weeks across the 16-week rearing period. These increases suggest that the enrichments had more generalized impacts in optimizing the behavioral development of the birds, resulting in more performance of behaviors that are believed to be positive for laying hens to engage in [43], and that, when thwarted, have been shown to increase the occurrence of abnormal behaviors [11].…”

“…One of the potential benefits of free-range systems is the increased space and outdoor environment that provides more freedom to exhibit behaviors that are viewed as part of a positive behavioral repertoire for hens [10]. These positive species-specific behaviors are typical natural behaviors that are not abnormal or negative (e.g., severe feather pecking, smothering) and hens show motivation to perform [11]. These include dust bathing and foraging (scratching and pecking at the ground) where environments that facilitate these (and other) natural behaviors are believed to provide positive welfare experiences for commercial hens [10].…”

Measurement of corticosterone in the plasma, eggs and faeces of laying hens

“…We have provided insight into the inputs that activate the HPA axis , and into the importance of the effects of corticosterone in tissue at the site of action in laying hens (Ralph et al 2015). Although there is evidence in both laying hens and broilers that physical handling can affect egg production (Hemsworth and Edwards 2020), currently, our knowledge in laying hens is not adequately advanced to understand the impact of the activity of the HPA axis from peripheral measures of corticosterone alone. Furthermore, interpreting the consequences of the actions of glucocorticoids from peripheral measures is complicated, because these hormones can have different physiological and behavioural effects in different circumstances and at different times (Tilbrook and Ralph 2017).…”

Effects of Captivity on the Morphology of the Insertion Sites of the Palmar Radiocarpal Ligaments in Hominoid Primates

“…However, some studies show naturalistic environments are important but not essential to generate adequate living conditions for their inhabitants [19]. Other authors stressed the importance of developing species-typical and natural behaviors [20], also called ethnological needs [21,22]. To achieve these behaviors, animals require complex environments and stimuli [23].…”