The recent increase in intensification of the UK dairy industry has led to the majority of cattle in the UK being housed in large, dynamic groups. Proposals for two large-scale dairies intending to house between 3,000 and 8,000 head of cattle have been met with considerable opposition by both producers and the public alike. Recent reports by both the Farm Animal Welfare Council and European Food Safety Authority have highlighted the continued welfare issues relating to dairy cattle, especially those housed in such large, dynamic groups. Conversely, with the current economic challenges being imposed on the UK dairy industry, there are many who see these systems as the future of dairying and discount the welfare concerns being highlighted. This project aimed to address one of the main welfare issues that receives scarce consideration when designing such systems; the social bonds of dairy cattle. A herd of 400 Holstein-Friesian cattle, plus followers, were observed in cubicle housing under commercial conditions. Through the identification of preferential relationships using an association index, important social bonds between individuals were identified. The majority of relationships between dyads were however weak, short term associations appearing together no more than once throughout the observation period. These bonds were significantly stronger in younger cattle demonstrated through the closer proximity maintained and the higher association index scores between dyads. Between the ages of 7 & 11 months animals performed the most positive social behaviour and had the strongest dyad relationships. In order to assess the strength of these positive relationships between dyads and to investigate the importance of these relationships to cattle, a short term (30 minutes) separation test from the remainder of the herd was carried out. Cattle’s responses to the challenge were assessed both physiologically and behaviourally. A significantly lower heart rate (p<0.01) during the separation period was observed when cattle were separated with their preferred partner compared to the non-preferred partner, and significantly lower levels of behaviour suggestive of agitation (p<0.05) were observed when they were with their preferred partner compared to when they were with the non-preferred partner. These results suggest that cattle were receiving social support from their preferred partners allowing them to have a reduced stress response to the social isolation test. As cattle aged and experienced regrouping, positive social bonds tended to disappear and cattle were more likely to have only weak associations. During long term separation (two weeks) from preferred partners, cattle showed significant behavioural, physiological and milk production changes. Upon subsequent reunion of preferred partners and consequential regrouping of individuals no further changes in behaviour, biology and milk production were observed, suggesting that separation rather than regrouping elicited a stress response. The bonds that had previously been evident between dyads were no longer present after the two weeks of separation. Subsequent relationships were also significantly weaker in focal cattle after separation of preferred partners and regrouping of animals. These results highlight the importance of relationships to the welfare of cattle and in particular the psychological well-being of cattle in commercial dairies. There is a significant need to reduce regrouping where possible and promote a more stable grouping system that enhances social bonds and positive social behaviour such as allogrooming; a behaviour which is currently rare in commercial systems. This will improve the quality of life for dairy cattle and increase their ability to cope with environmental challenge such as at times of regrouping and separation. In conclusion, social bonds do occur in domesticated dairy cattle and can be found when living in large dynamic group systems, but they are significantly affected by separation at the time of regrouping. These social bonds are important to the welfare and well-being of cattle; practices that promote stability and positive associations will be beneficial to the welfare of animals.