Precision livestock farming (PLF) systems have the potential to improve animal welfare through providing a continuous picture of welfare states in real time and enabling fast interventions that benefit the current flock. However, it remains unclear whether the goal of PLF development has been to improve welfare or increase production efficiency. The aims of this systematic literature review are to provide an overview of the current state of PLF in poultry farming and investigate whether the focus of PLF research has been to improve bird welfare. The study characteristics extracted from 264 peer-reviewed publications and conference proceedings suggest that poultry PLF has received increasing attention on a global scale, but is yet to become a widespread commercial reality. PLF development has most commonly focussed on broiler farming, followed by laying hens, and mainly involves the use of sensors (environmental and wearable) and cameras. More publications had animal health and welfare than production as either one of or the only goal, suggesting that PLF development so far has focussed on improving animal health and welfare. Future work should prioritise improving the rate of commercialisation of PLF systems, so that their potential to improve bird welfare might be realised.

Evolutionary change requires natural selection in the presence of heritable variation for the trait(s) under selection. Since heritabilities and selection pressures are known to vary with environmental conditions, it is crucial to know how much genetic variation is expressed under which conditions. This study addresses the question of how the expression of genetic variation for fledgling body size of Great Tits varies with the environment. Different environmental conditions were created experimentally by manipulating brood sizes. The treatment affected body size, measured as either fledging weight or tarsus length, and interacted with natural temporal variation in food availability. Both measurements show stabilizing selection.A cross‐fostering design was carried out to separate genetic and environmental causes of variation. Heritabilities as measured from offspring‐midparent regressions and from full‐sib analyses were substantial for both traits, except that no heritability was found for weight under poor conditions. Instead, fledging weights were significantly correlated with the weights of their unrelated guardians' ( = fosterparents') weight under poor conditions.We propose that under poor conditions, when selection on fledging weights is expected to be directional and strong, only little genetic variance is expressed. Any evolutionary response to this selection on fledging weight might therefore be slow, if the increase in selection pressure is not greater than the decrease in heritability.

Keel bone fractures and deviations are one of the major welfare and health issues in commercial laying hens. In non-cage housing systems like aviaries, falls and collisions with perches and other parts of the housing system are assumed to be one of the main causes for the high incidence of keel bone damage. The objectives of this study were to investigate the effectiveness of a soft perch material to reduce keel bone fractures and deviations in white (Dekalb White) and brown laying hens (ISA Brown) kept in an aviary system under commercial conditions. In half of 20 pens, all hard, metal perches were covered with a soft polyurethane material. Palpation of 20 hens per pen was conducted at 18, 21, 23, 30, 38, 44 and 64 weeks of age. Production data including egg laying rate, floor eggs, mortality and feed consumption were collected over the whole laying period. Feather condition and body mass was assessed twice per laying period. The results revealed that pens with soft perches had a reduced number of keel bone fractures and deviations. Also, an interaction between hybrid and age indicated that the ISA hybrid had more fractured keel bones and fewer non-damaged keel bones compared with the DW hybrid at 18 weeks of age, a response that was reversed at the end of the experiment. This is the first study providing evidence for the effectiveness of a soft perch material within a commercial setting. Due to its compressible material soft perches are likely to absorb kinetic energy occurring during collisions and increase the spread of pressure on the keel bone during perching, providing a mechanism to reduce keel bone fractures and deviations, respectively. In combination with genetic selection for more resilient bones and new housing design, perch material is a promising tool to reduce keel bone damage in commercial systems.

Measuring the ratio of heterophils and lymphocytes (H/L) in response to different stressors is a standard tool for assessing long-term stress in laying hens but detailed information on the reliabil...