Factors associated with the variation and consistency of social network position in group-housed calves

Abstract

Gregarious animals often choose to interact with other individuals based on characteristics such as sex, age, and body size. However, we know little about the social structure and development of group-housed dairy calves. The aim of this study was to determine factors influencing a calves’ social network position and assess individual consistency over time. Holstein calves were group-housed (9 groups; 10 calves/group) at 15 ± 2.9 d of age (mean ± SD). Calves were weaned over 10 d beginning at 47 ± 2.5 d of age (mean ± SD) and remained in the study until 1 week after weaning. Continuous positional data were recorded within the pen using an ultra-wideband positioning system. Non-directed weighted matrices representing the social networks of calves (heifer: n = 55; bull: n= 32; excluded calves: n = 3) were constructed for each group consisting of consecutive 4-day periods per week over a total of 6 weeks. Social network position was measured using three centrality measures: strength, eigenvector, and closeness. To determine the factors that influence social structure, LMMs were used to test fixed effects of sex, ADG, age at grouping, season (warm or cool), and stage of development (pre-weaning, weaning, and post-weaning), with group and calf ID as nested random factors. Sex, weekly ADG, age at grouping, and season weren’t significant predictors of strength centrality. However, stage of development was a significant predictor for strength (p <.001) and closeness centrality (p <.001), with the highest scores found during the pre-weaning period and lowest during post-weaning. This suggests that calves were associating with more individuals in the early weeks of group formation and were more discerning with social interactions as time went on. The only predictor for eigenvector centrality was season (p =.04), with calves exhibiting higher eigenvector centrality during the cooler months. Strength and closeness centrality measures were significantly repeatable across weekly social networks for all groups (strength: R = 0.31 - R = 0.85, closeness: R = 0.27 - R = 0.89) and consistent across stage of development for 6 of the 9 groups (strength: R = 0.38 - R = 0.80, closeness: R = 0.33 - R = 0.87). Our results suggest that the amount of time spent within a group may play a role in shaping associations in dairy calves, but that dynamics of sociality and network structure may also be driven by individual and life-history traits.