Effects of shade on milk production in Swedish dairy cows on pasture
Heat stress negatively influences the performance of dairy cattle such as lactation and reproduction. Heat stress can cause production losses as well as welfare problems. Years of research have shown that heat stress is a huge problem for dairy cattle in both the tropics and temperate zones but no such research have so far been done in northern European countries. It seems like shade is an important tool when improving pasture conditions and therefore
deserves more attention. The aim with this study was to investigate whether there is a need of providing shade for grazing dairy cows during the summer in Sweden.
Two groups of lactating Swedish Red dairy cows (n=15 per group) were kept on pasture. To evaluate the effects of shade, one of the groups had access to shade (group 1) and the other had not access to shade (group 2). Metrological data such as ambient air temperature (°C),relative humidity (%) and black globe temperature (°C) were measured both on the inside and outside of the tent and temperature-humidity indexes (THI) were calculated. Other measured parameters were daily milk yield and occasional fur temperature, rectal temperature and respiration rate. During days with warm and sunny weather also milk composition were
analyzed for each cow. The trial did also include behaviour studies of the cows. These data are however not analyzed in this thesis which instead focus on milk production and
physiological parameters of the cows.
The ambient temperature varied between 7.3°C and 33.1°C during the trial period with a daily mean temperature of 18.5°C. THI values calculated for the outside of the tent, varied from 45.5 to 79.6. Both mean and max temperature and THI was lower inside the tent compared to outside the tent. On 13 of the days associated with milk samples THI-values ?72 were observed. Also THI-values over 78 (which are considered to cause extreme heat stress)occurred occasionally.
The cows with access to shade chose to use it but the results from the trial showed no significant effects of the weather variables on the milk production. However, THI and
ambient air temperature had a significant effect on respiration rate and fur temperature for the cows in both treatment groups. But temperature and THI did not affect rectal temperature and no difference in rectal temperature between the two groups of cows could be seen.
In conclusion, access to shade did not affect the milk production but it seemed as the shade had a cooling effect on the cows which was demonstrated by the results of lower fur temperature and respiration rate for the cows with access to shade. Even though the study did not verify the importance of shade for grazing dairy cows from an economic perspective, the fact that the cows with access to shade also used the opportunity to be in shade, indicates that
shade on pasture is important for the cow from a well-being perspective.