2. Material and methods
2.1. The experimental animals
Seven Norwegian Red calves (four heifers and three bulls) born four days apart were borrowed from a dairy farm south of Oslo, Norway. One of the heifer calves became ill before the test period and was therefore excluded. The animals were 19–23 days of age at the beginning of the experiment. All experimental animals were weighed upon arrival (day 0) and before each test session. The calves weighed between 39.5 and 48.5 kg at arrival. The calves were housed in a group pen (4 by 4 m) at the Norwegian University of Life Sciences in Oslo. The calves were fed according to the recommended Norwegian feeding regime at the time and received 2 l of warm whole milk three times per day at 8 am, 1 pm and 6 pm. The animals had free access to water, hay and concentrates.
All experimental procedures were in accordance with the regulations controlling experiments/procedures on live animals in Norway, and the study complies with the policies relating to animal ethics. Due to the nature of the experiments, permission from the Norwegian Animal Research Authority was not required. All calves were returned to their owner after the experiment.