Study suggests negative impact caused by feelings of hunger.

A new study has found that a reduction in the milk allowance of calves makes it harder for them to focus and learn. The paper, published in the Royal Society’s Biology Letters, argues that the impact on calves’ cognitive abilities is consistent with negative feelings of hunger.

Dairy calves are commonly weaned from milk to solid feed at an earlier age than they would be naturally. The researchers, based at the University of British Columbia, Canada, wanted to study how this change in diet affects the subjective experience of calves.

To test the impact, the researchers conducted two experiments using a modified hole-board test. In the first experiment, the calves had to remember the location of four bottles that contained milk that were placed among 11 empty bottles. In the second experiment, the bottles containing milk were moved and the calves had to relearn where the bottles were. During the experiments, the amount of milk fed to the calves was reduced.

Both experiments showed that cognitive performance declined. When milk allowance was reduced, calves found it harder to remember which bottles contained milk and were slower to learn the new locations when the bottles were moved.

The study does not directly prove that the calves were feeling too hungry to focus and learn, but the researchers conclude that the results are consistent with distressful feelings of hunger. They cite an increase in vocalisations as further evidence of negative emotions.

Dr Ben Lecorps, one of the contributors to the study, said: ”We need to know more about what calves feel if we want to change routine farm practices to improve their welfare. Although we may never be able to fully understand what a calf feels or thinks, this type of study gets us closer to this goal.

"Our results support the growing body of evidence that weaning from milk can induce hunger, particularly when animals are pushed to switch to solid feed (by decreasing milk allowances) abruptly. Our study also shows that it may be hard for calves to learn new tasks when they are experiencing high levels of hunger, which is concerning because it may slow down how fast they learn to feed from another source.”

Dr Lecorps, an animal welfare lecturer at the Bristol Veterinary School, intends to carry on researching the topic with his graduate students. The next stage is to compare the cognitive abilities of calves who are fed restricted amounts of milk with calves fed milk without restrictions.