Behavioural responses to climatic demands of dairy heifers housed outdoors

The aim of the present study was to investigate the behavioural responses t o different climatic demands of growing dairy heifers, during winter at a l atitude of 60 degreesN. Two groups (n = 11, 12) of yearling dairy heifers w ere housed in two similar 3-ha enclosures, characterised by deciduous fores t, ley and pasture. Each enclosure also contained a lying area, a heated wa ter source and a feed bunk from which the heifers had free access to grass silage. The behaviour and location of each heifer were recorded by instant interval observations every 5 min between 0600 h and 2000 h during 23 obser vation days spread over the entire winter period. Outdoor temperature, wind speed and solar radiation were measured continuously. The climatic energy demand (CED, W m(-2)) was measured with a heated animal model. The climate had significant effects on all the main activities and on the location of t he heifers. Higher CED values corresponded to a greater number of observati ons of heifers in the lying area, and a greater incidence of lying and of r uminating, but to a decreased incidence of eating and grazing. Increased mi gration to the forested areas instead of to open areas reflected increasing CED values. The results from the present study show that dairy heifers ada pt their behavioural activity and choice of location to the climatic condit ions, to reduce energy expenditure. Thus, dairy heifers can be sustained in a cold climate if they are provided with wind breaks and dry lying places.