Dairy Cows, Allogrooming, And Welfare
Dairy cows are herd animals who thrive in socially stable groups. In modern dairy production systems, naturally-occuring herd dynamics can be (and often are) disrupted, as cows in a herd are usually divided into groups based on their stage in the dairy-production process. Of particular importance is the transition period from 3 weeks before calving to 3 weeks after calving, when cows are exposed to many stressors, including regrouping, calving itself, diet changes, onset of lactation, and calf separation. Regrouping is well-established as a negative influence on behavior, welfare, and productivity of cows, as cows must recover from broken social bonds and form new ones.
Social grooming serves a variety of functions in dairy cows, including establishing, maintaining, and reinforcing social bonds. Grooming can enhance group cohesion, maintain social stability, and reduce social tension. Analyzing grooming behavior can provide information on how social networks evolve and how resilient grooming is to group disturbances.
To gather this information, the authors of the present study observed grooming behavior of a group of 38 pasture-based dairy cows for 4 hours per day, 5 days per week over the course of 6 weeks. Cows were enrolled in the study after separation from calves, and joined the study at various times. The study had two aims: 1) to determine the relationship dynamics between lactating dairy cattle using social grooming, and 2) to explore factors that could shape changes in social grooming between individual cattle. In addition to grooming behavior, headbutting behavior was observed and recorded, and used to measure status hierarchy.
The observed data was fed into a mathematical model, which analyzed the social networks which emerged from grooming behavior. A given cow was unlikely to groom every other cow, and cows in general were more likely to groom cows who groomed them, indicating a reciprocity effect. Intensity of performing and receiving grooming varied greatly, indicating individual differences among cows. Factors that influenced grooming patterns included age, familiarity, social rank, and timing of joining the study. Some cows were central to the social network, while others existed more on the periphery.
For animal welfare advocates, the most useful insights relate to dairy cow welfare. From week to week, as new cows joined the study, the density of the social network decreased, indicating a less complex grooming structure. Once cows stopped joining the study, network density began rising again, and returned to its week 1 value during week 6. Once the group was set and no new cows joined the study, stable ties increased, but there was a considerable reorganization of ties over the course of the 6 weeks.
The authors conclude that overall, the social network was stable. They hypothesize that variability in grooming patterns may reflect underlying processes of cooperation, reciprocity, and social roles. They recommend future studies to examine these processes, especially be comparing before-calving and after-calving networks.