Long-term familiarity creates preferred social partners in dairy cows

Highlights

• Group is an essential resource for gregarious animals.

• We investigated whether dairy cows maintain social relationships in an unstable social environment.

• Long-term familiarity significantly increased intensity of social relationships.

• Keeping well-acquainted cows together may promote dairy cow welfare.

Abstract

Group is an essential resource for gregarious animals. Dairy cows are however frequently (re-)grouped according to productivity and reproductive state leading to an unstable social environment for the animals. The present study aimed at investigating whether cows maintain social relationships in a dynamic group. Therefore we analysed whether more familiar cows spend more time in close proximity, and interact more often in an affiliative way. Social interactions and direct neighbours during feeding and resting of 12 Holstein cows (1st to 3rd lactation) in a dynamic dairy cow group of 50 animals were assessed continuously over four days using focal animal sampling. A principal component analysis over the twelve assessed social behaviour variables per pair revealed four main components: social relationships may be characterised by time spent as direct neighbours when feeding and interacting affiliative as well as agonistically (excluding displacements), by displacement success, allogrooming interactions, and time spent as direct neighbours when resting. Long-term (shared youth experience, shared adult experience) and short-term (shared dry-period, synchronised group entry) familiarity was associated with higher scores for interacting and being direct neighbours when feeding (p < 0.05 for shared youth experience, shared adult experience, and shared dry-period), allogrooming (p < 0.1 for shared adult experience × shared dry-period), and being direct neighbours when resting (p < 0.05 for shared youth experience × shared adult experience). Long-term familiarity had a stronger effect on the intensity of social relationships, i.e. regarding investment of time and energy, than very recent shared experience. These results support the notion that dairy cows actively maintain valuable dyadic relationships. In practical terms, keeping well-acquainted cows together may contribute to a stable inner structure of a dairy herd and thus promote dairy cow welfare.

Introduction

Group is an essential resource for gregarious animals, and as such potentially related to biological fitness, health and welfare (Mendl and Held, 2001, Špinka, 2012). Isolation, the risk of social exclusion, or threat to social bonds elicit physiological and behavioural stress responses (Aureli and Smucny, 2000). Proximity, security, or assurance of social bonds on the other hand elicit responses that facilitate and reinforce to maintain the situation. In the long-term, such a physiological and emotional state has ‘stress-buffering’ effects, i.e. it promotes coping with and recovery from non-social as well as social stress (Cohen and Wills, 1985, Kikusui et al., 2006). A secure and positive social environment therefore has beneficial short-term as well as long-term effects both on psychological and physiological health and resilience (Hennessy et al., 2009, Karelina and DeVries, 2011). There is growing interest in considering this so-called ‘social buffering’ in farm animal health and welfare (Rault, 2012). The importance and complexity of individual dyadic relationships within a group and their potential social buffering effectiveness differ between and also within species depending on various factors including ecological aspects, social structure, strength of bonding or relationship quality (Hennessy et al., 2009, Pollard and Blumstein, 2012). Either way, social interactions form the basis: social structure can be divided into patterns of individual social relationships differing in nature and quality, that are in turn defined by content, quality and patterning of social interactions (Hinde, 1976). Depending on the physical appearance of the involved animals, e.g. muscle tension and strain, and depending on the outcome of an interaction, i.e. roughly said whether the distance between the animals is reduced, maintained, or increased, interactions are distinguished into affiliative, neutral and agonistic ones to describe animal social relationships.

Based on observations of extensively kept or semi-wild domestic cattle groups (Schloeth, 1961, Hall, 1983, Reinhardt et al., 1986), cattle ancestors lived in stable groups of largely related females and their young offspring, and probably experienced fission–fusion dynamics, i.e. temporarily joining with and splitting from other groups for foraging, resting, or migrating (Cornélis et al., 2014, van Vuure, 2014). Such a social environment is supposed to promote individualised long-lasting, complex, and valuable relationships (Hamilton, 1964, de Waal and Tyack, 2003, Aureli et al., 2008). Cases of ‘friendship’ have been reported among adult cattle (Sambraus, 1976) and are frequently mentioned in standard textbooks on cattle social behaviour (Bouissou et al., 2001) even though systematic and hypothesis-driven studies on relationship quality in cattle are lacking.

For dairy cows, loose group housing is nowadays widely implemented, facilitating choice of social partners and expression of social behaviour. However, the social environment in large-scale dairy herds of hundreds of animals is fragile and demanding: It is well documented that husbandry routines, namely regrouping, large group-size, and high stocking density, lead to an increase of agonistic interactions combined with a decrease in feeding and lying time (Raussi et al., 2005, DeVries and von Keyserlingk, 2006, Huzzey et al., 2006, Gupta et al., 2008, von Keyserlingk et al., 2008, Hill et al., 2009), have effects on fertility (Dobson et al., 2001), weight gain and health in calves (Pedersen et al., 2009), and productivity (Arave and Albright, 1976, Brakel and Leis, 1976, von Keyserlingk et al., 2008). On the other hand, results of regrouping experiments comparing single versus pair- or groupwise integration into a herd provide evidence that the presence of familiar peers positively influences behaviour and helps to alleviate stress (Bøe and Færevik, 2003; for calves: Færevik et al., 2007, O’Connell et al., 2008, Gygax et al., 2009). In large intensive systems, social adaptability could conceivably be overstrained and dairy cows may no longer be able to maintain individualised relationships. The possible consequences of living in an unstable and rather anonymous social environment on emotional and physiological wellbeing, health and resistance, and on the ability to benefit from the group through social buffering of stressful events, or positive emotional experiences, have rarely been considered yet (Jóhannesson and Sørensen, 2000, DeVries et al., 2003a, Rault, 2012).

The present study therefore aimed at investigating whether indicators of preferential social relationships differ between pairs of dairy cows depending on their familiarity. Our hypothesis was that cows seek to maintain stable relationships and therefore spend more time and interact more often in an affiliative way with their most familiar herd mates. Social relationships among cows were assessed on the basis of time they spent in close proximity and frequencies of social interactions, which are common means in the study of non-human animals’ social relations (Whitehead, 2008).