Abstract
For farmed species, good health and welfare is a win-win situation: both the animals and producers can benefit. In recent years, animal welfare scientists have embraced cognitive sciences to rise to the challenge of determining an animal's internal state in order to better understand its welfare needs and by extension, the needs of larger groups of animals. A wide range of cognitive tests have been developed that can be applied in farmed species to assess a range of cognitive traits. However, this has also presented challenges. Whilst it may be expected to see cognitive variation at the species level, differences in cognitive ability between and within individuals of the same species have frequently been noted but left largely unexplained. Not accounting for individual variation may result in misleading conclusions when the results are applied both at an individual level and at higher levels of scale. This has implications both for our fundamental understanding of an individual's welfare needs, but also more broadly for experimental design and the justification for sample sizes in studies using animals. We urgently need to address this issue. In this review, we will consider the latest developments on the causes of individual variation in cognitive outcomes, such as the choice of cognitive test, sex, breed, age, early life environment, rearing conditions, personality, diet, and the animal's microbiome. We discuss the impact of each of these factors specifically in relation to recent work in farmed species, and explore the future directions for cognitive research in this field, particularly in relation to experimental design and analytical techniques that allow individual variation to be accounted for appropriately.
Highlights
Understanding the cognitive capabilities of animals, how they may be affected by the environments in which we keep them, and the extent to which these changes can be used as an indicator of welfare, are increasingly of interest in the field of animal welfare
We explore the main causes of within- and between-individual variation in cognitive testing of livestock
Drawing from the studies that have found a breed-related association with performance, the results suggest that cognition is influenced by an animal’s evolutionary, ecological and developmental environment [102]
Summary
Understanding the cognitive capabilities of animals, how they may be affected by the environments in which we keep them, and the extent to which these changes can be used as an indicator of welfare, are increasingly of interest in the field of animal welfare. It should be noted that, when exploring sources of variation in cognitive testing, the test itself could be a contributing factor One example of this is side preference, which can develop in T-maze or Y-maze study designs, as shown in a variety of species including sheep [103], rats [104], and cows [105]. Cognition and behavior are hierarchically organized and continuously interacting with endogenous (e.g., life stage) and exogeneous (e.g., the behavior of conspecifics, developmental environments) factors This likely results in correlations between many different cognitive and behavioral variables [referred to as the “crud factor” in human psychology; [106]], as well as their significant associations with endogenous and exogenous variables, but these do not necessarily reflect direct causal relationships. Ewes exposed to stressful situations during late pregnancy produced lambs that showed increased levels of fear and a decreased ability to navigate a TABLE 1 | An overview of cognitive tests that have previously been used in farmed species and the type of cognitive ability they assess
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