Indoor-housed dairy heifers' motivation to access an additional space.

Dairy heifers are often housed in confined environments that can limit the range of behaviors they express. Previous studies have assessed the motivation of indoor-housed dairy cows for specific resources, such as pasture or brushes, by comparing the weight animals are willing to push to access these resources relative to an empty space. However, little is known about how much confined cattle value access to additional space itself. We assessed the use of, and motivation to access, additional space in dairy heifers housed in a freestall barn. Holstein heifers (n = 48; mean age: 7.1 ± 0.74 mo; mean BW: 279.8 ± 32.57 kg) were housed in 4 groups of 12 in pens (7 m x 12 m) containing 13 lying stalls, a waterer and 35 cm of feed bunk space per animal. Groups were given 3h/d access to an additional space (23 × 2 m, sand-bedded) adjacent to the home pen under both a free access phase (i.e., with no restriction) and a weighted gate phase (i.e., requiring heifers to push a progressively heavier weight). All heifers used the additional space when provided free access, but the number of animals entering the space declined when access was restricted via a weighted gate. Variation among groups and individuals was observed in both how much time heifers spent in the space and expressed motivation, with maximum weight pushed ranging from 1.5 to 22.5 kg. Heifers willing to push the most weight actually spent less time using the space when access was free. Additionally, heifers' use of the additional space appeared to be influenced by the movements of herd mates. These findings indicate that dairy heifers housed in freestall barns are motivated to access additional space, suggesting that greater opportunities for movement should be considered in housing design and that "empty space" may not represent an appropriate negative control in motivation studies.