A tacit assumption in laboratory animal research is that animals housed within the same cage or pen are phenotypically more similar than animals from different cages or pens, due to their shared housing environment. This assumption drives experimental design, randomization schemes, and statistical analysis plans, while neglecting social context. Here, we examined whether a domain of social context—social dominance—accounted for more phenotypic variation in mice than cage-identity. First, we determined that cages of mice could be categorized into one of three dominance hierarchies with varying degrees of dominance behavior between cage-mates, and low levels of agonistic behavior in the home-cage. Most groups formed dynamic hierarchies with unclear ranks, contrasting with recent accounts of stable transitive hierarchies in groups of mice. Next, we measured some phenotypic traits, and found that social dominance (i.e. dominance hierarchy type and degree of dominance behavior) consistently accounted for some phenotypic variation in all outcome measures, while cage-identity accounted for phenotypic variation in some measures but virtually no variation in others. These findings highlight the importance of considering biologically relevant factors, such as social dominance, in experimental designs and statistical plans.

When infected, animals change their behaviors in several ways, including by decreasing their activity, their food and water intake, and their interest in social interactions. These behavioral alterations are collectively called sickness behaviors and, for several decades, the main hypotheses put forward to explain this phenomenon were that engaging in sickness behaviors facilitated the fever response and improved the likelihood of host survival. However, a new hypothesis was recently proposed suggesting that engaging in sickness behaviors may serve to protect kin. We tested this kin protection hypothesis by combining a field and a laboratory experiment in house mice. In both experiments, we induced sickness behaviors by administration of a pro-inflammatory agent. In the field experiment, we then collected genetic data and assessed whether relatedness affected the intensity of sickness behaviors. In the lab experiment, we manipulated relatedness in small social groups and assessed whether having a closely related individual (a sibling) in the group altered social interactions or visits to common resources (such as food and water containers) once immune-challenged. Our results do not support the kinship protection hypothesis and therefore advance our understanding of why such an apparently costly set of behavioral changes would be evolutionarily maintained.

The continuous direct exposure to solar radiation, coupled with their own metabolic heat production, make grazing dairy cows on pasture particularly susceptible to heat stress. Heat stress can impair performance, animal welfare, and health. The objective of the present study was to identify physiological indicators of heat stress in dairy cows in a pasture-based production system under moderate climate conditions. The study was performed with 24 lactating Holstein dairy cows during summer 2018 and 2019 at the experimental farm of Agroscope (Posieux, Switzerland). Cows grazed full-time using a set stocking system. Climate conditions were recorded every min and were used to calculate the comprehensive climate index (CCI), which reflects the felt temperature in °C. The vaginal temperature (VT) of each cow was measured every 10 minutes with temperature loggers and was used as a physiological indicator of heat stress. Blood and milk were sampled once daily in the afternoon before and during milking, respectively. The concentrations of thyroxine (T4) and triiodothyronine (T3) were analyzed in blood plasma and cortisol concentration was analyzed in milk. Data from 12 periods of up to 3 consecutive days with increasing CCI was analyzed. Analysis were performed with the averaged CCI and the maximal VT recorded between 0830 and 1430 h. The VTmax was positively correlated with CCIaverage (P < 0.001). The T4 and T3 concentrations decreased with increasing CCIaverage and VTmax (P < 0.01). Cortisol concentrations were positively correlated with CCIaverage and VTmax (P < 0.05). Changes in VT and hormones showed that cows responded to increasing environmental temperature and may have perceived the rising heat load as a stressor.

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