Laterality of lying behaviour in dairy cattle

Dairy cattle spend, on average, between 8 and 15h/d lying down. Our objective was to describe the laterality of lying behaviour and assess several internal and external factors that may affect laterality. Internal factors included time spent and time since eating or lying before choosing to lie down again. External factors included the slope and the amount of bedding on the of the lying surface. The dependent variables were the proportion of time spent lying on left versus right sides (as affected by eating and by the slope of stalls) and the probability of switching sides between two consecutive lying bouts (as influenced by previous lying bouts and the amount of bedding). The proportion of time on the left and right sides matched the mixed pattern in the literature; some groups of cows (n =35, non-lactating, freestall housed) spent more time (56±3.0%, P =0.042) on their left side, while other groups (n =151, housed either in a freestall barn or at pasture) showed no preference for lying on one side versus the other (50±1.2% on left side, P >=0.308). Laterality while lying was not influenced by eating behaviour or by the slope of the lying surface. Overall, cattle switched sides in 64% of consecutive lying events, more than 50% expected by chance (SE=0.8%, P <0.001). Switching sides was influenced by previous lying behaviour: cattle were more likely to switch sides if the previous lying bout was either long or recent (1.5±0.33 and 1.1±0.21% change in probability of switch for every 10min in the last lying bout and for every 10min since previous lying event, respectively, P <0.001). Cows were more likely to switch sides when housed on mattresses with more bedding (switched sides in 68, 77, and 97±10.8% lying events for 0, 1 and 7.5kg of sawdust bedding, mean±SE, P =0.042), possibly because cows had more lying events with shorter intervals between these events when the stall surface was well bedded. The probability of terminating a lying bout was also influenced by the duration of the bout. For example, during the first 10min of a lying bout, the probability of standing up was only 5% but climbed to approximately 25% when the bout lasted 80min or more. In conclusion, overall laterality in lying behaviour is shifted to the left in some groups but not others. Eating behaviour has little effect on time spent lying on either side. Cows switched sides between consecutive lying bouts and switching was more likely if the previous bout was either recent or long. Finally, continuous lying may become uncomfortable when bouts are longer than 80min, and cows may switch sides to alleviate this discomfort.