The importance of shade for dairy cattle in Sweden.

Abstract: Today, there are no regulations saying that cows must have access to some kind of shelter at pasture during the summer. In more tropical countries, it is well-known that dairy cows might suffer from heat stress when exposed to sun and high temperatures. The well-being of the cows is thereby reduced and the production may also decrease. In Sweden, no research has been done in the area and therefore it is now a clear need of improved knowledge.The purpose of this study was to investigate the importance of shade for dairy cows in Sweden. The behaviour of 30 cows was examined to see any differences between cows with access to shade and cows without access to shade. The cows were divided into two groups with fifteen cows in each group. At pasture, one group had access to shade in a tent (group 1) and the other group did not have access to shade (group 2). Behavioural observations were carried out at thirteen occasions, including four 24-h-periods. The behaviour of all cows and whether they were positioned in shade or not were recorded in 10-minute intervals. The microclimate was measured at regular intervals of 10 minutes using HOBO dataloggers, and Temperature-humidity index (THI) was calculated from the ambient temperature and relative humidity. The milk yield was measured at each milking and when the temperature outside was high, milk samples were taken to measure the components and the somatic cell count of the milk. Grass samples were also taken to measure the quantity of pasture in dry matter content and energy as well as the grass components. The results showed that cows starts using shade at a THI of 66.9 and their shade use increased as THI increased. They used the tent in average 14.5 % of the time per day between 9 am to 7 pm. The most common behaviour within the shade was standing. As THI increased, grazing behaviour declined, and to compensate this they grazed to a higher extent during the night. The cows also stood up, moved around and lied down to a higher extent when THI increased. The cows grazed to the highest extent between 5 pm and 10 pm, and lied down to the most between 2 am and 6 pm. The group without shade showed the highest frequency of both grazing and lying. These results indicate that dairy cows in Sweden prefer to use shade if available when the temperature and relative humidity is high. However, more research is needed to see if the well-being is reduced by the absence of shade.