Phenotypic integration describes the complex interrelationships between organismal traits, traditionally focusing on morphology. Recently, research has sought to represent behavioural phenotypes as composed of quasi-independent latent traits. Concurrently, psychologists have opposed latent variable interpretations of human behaviour, proposing instead a network perspective envisaging interrelationships between behaviours as emerging from causal dependencies. Network analysis could also be applied to understand integrated behavioural phenotypes in animals. Here, we assimilate this cross-disciplinary progression of ideas by demonstrating the use of network analysis on survey data collected on behavioural and motivational characteristics of police patrol and detection dogs (Canis lupus familiaris). Networks of conditional independence relationships illustrated a number of functional connections between descriptors, which varied between dog types. The most central descriptors denoted desirable characteristics in both patrol and detection dog networks, with ‘Playful’ being widely correlated and possessing mediating relationships between descriptors. Bootstrap analyses revealed the stability of network results. We discuss the results in relation to previous research on dog personality, and benefits of using network analysis to study behavioural phenotypes. We conclude that a network perspective offers widespread opportunities for advancing the understanding of phenotypic integration in animal behaviour.

The hypothalamic–pituitary–adrenal (HPA) axis responsivity is influenced by early life experience and also modified by the environment an individual experiences as an adult. Because laying hens are transferred from rearing to laying farms at 16–18 weeks of age, they are well suited to study the interaction effect between early (rearing) and adult (laying) environments on physiology and behaviour. In the European Union, there is a move towards cage-free systems for laying hens, but globally, the majority of layers are kept in conventional or furnished cages. Conventional cages have no enrichment, whereas furnished cages have little enrichment. Both cage types limit the movement of birds and the expression of highly motivated behaviours. Lack of enrichment may lead to under-stimulated birds that are more sensitive to stress and fear-inducing challenges later in life. Fearfulness has been linked to feather pecking, which has negative consequences for animal welfare and productivity. Previous research has shown that birds reared in cages are more fearful and perform more poorly in a test of spatial cognition than birds reared in aviaries when tested within five weeks after transition to adult housing. However, recent results suggest that these effects might not be long-lasting. We, therefore, tested the effect of the early (rearing) (aviary vs. cage) and adult (laying) environments (standard vs. additionally enriched furnished cages) on the corticosterone response to restraint in birds that were 35 weeks into lay (i.e., 52 weeks of age) and assessed their plumage condition. We hypothesised that a lower level of enrichment, both during rearing and adulthood, would represent a lower level of stimulation, resulting in a stronger corticosterone response to restraint and poorer feather cover. Both stressed (restrained) and control birds increased their corticosterone levels from the first (baseline) to second sample (p < 0.01 for both), but the increase in the restrained group was significantly higher than in the control group (F1, 111 = 9.51; p = 0.003). There was no effect of the early environment, but birds housed in standard furnished cages as adults had overall higher corticosterone levels than birds housed in enriched furnished cages regardless of their early life environment (F1, 51 = 4.12; p = 0.048). Neither early nor adult housing influenced the feather score except for on the belly, where birds housed in enriched cages as adults had a poorer feather score, contrary to our prediction. In conclusion, no effect of the early environment on HPA axis responsivity to an acute stressor could be detected at 52 weeks of age, but adult enrichment had a favourable effect on overall corticosterone levels.

The effect of the enrichment (10% ad libitum daily feed intake) with live larvae of Hermetia illucens (HI) was evaluated on behavior, egg production and quality from 36 to 40 weeks of age in 1800 laying hens of two genotypes (brown and white) randomly allocated in 8 pens of an aviary system. The larvae enrichment significantly affected space use and behavior, increasing the number of birds on the floor (P < 0.001), the proportion of clean eggs and that of eggs laid in the nest (P = 0.001), while reducing inactivity, floor pecking and the distance hen-operator at the avoidance test in enriched compared to non-enriched pens. As for differences between genotypes, the rate of inactive hens was higher (P = 0.001) in brown compared to white hens, while the rate of hens pecking the floor and showing preening was lower (P < 0.001). The number of piling events was markedly lower in brown compared to white hens (P < 0.001) and brown hens were also more likely to approach a novel object (P = 0.044). Then, brown hens showed higher rates of broken eggs (P = 0.008), fewer eggs laid in nests and more eggs laid on aviary tiers (P < 0.001). Egg quality differences were limited with more blood and meat spots (P < 0.001), lower yolk proportion (P < 0.001) and thicker shells (P < 0.001) in brown compared to white hens. In conclusion, the enrichment with HI live larvae increased species-specific behaviors in both genotypes without substantially affecting egg production and/or quality. On the other hand, the enrichment improved the space use as eggs laid in the nests increased at the expenses of floor eggs, which finally resulted in an improvement of production.