RESUMO
Several factors influence whether dairy cattle prefer to be indoors or at pasture, including weather conditions and milk yield, but it is unclear how motivated cows are for access to pasture. One way to measure motivation is to require the animal to work (e.g., walk different distances) for access to a resource. This study investigated whether pasture access located 60, 140, or 260m from the indoor housing would affect the proportion of time dairy cows spent at pasture. Thirty-two Holstein-Friesian dairy cows were used during the study, which took place in the United Kingdom from May to July 2010. The experiment consisted of four 18-d experimental periods, with 8 cows in each period, which were further divided into 2 groups of 4 cows. Following a training period, the cows were randomly allocated to distances of 60, 140, or 260m to pasture over three 4-d measurement periods. A video camera was used to record time spent indoors and outdoors 24h/d, and manual behavior observations (0700 to 2200h) took place 6 times during each period to record how the cows spent their time in each location. The video data showed that cows spent, on average, 57.8% (±3.44) of their time outside (either at pasture or on the track). One-sample t-tests revealed that this value was different from 0% (t=16.80), 50% (t=2.26), and 100% (t=-12.28). Analysis of the percentage time spent outside revealed that distance did not influence nighttime pasture use (2100 to 0430h; F2,8=0.16; 81.0% vs. 81.0% vs. 76.7%, for 60m vs. 140m vs. 260m, respectively). In contrast, during the day (0700 to 2100h; from behavior observations), time spent at pasture declined as distance increased; that is, cows spent more time at pasture when they had to walk 60m (F2,80=10.09) than when they had to walk 140 or 260m (45.3% vs. 27.4% vs. 21.2%, respectively). Time spent at pasture decreased on rainy days (y=-1.0672x + 59.646, R(2)=0.09, n=48d), but the indoor temperature-humidity index (THI), the outdoor THI, and body condition score did not influence time spent outside. Under the climatic conditions of the current study in the United Kingdom, cows had a partial preference for pasture, which was influenced by distance to pasture during daytime but not at night. This shows that dairy cows were more motivated to access pasture at night compared with during the day.
