A recent study has found that a reduced milk allowance can disrupt calves’ ability to focus and learn, and can result in them experiencing negative feelings of hunger.
The study, carried out by the Bristol Veterinary School and published in the Royal Society Biology Letters, experimented with the effects of milk restrictions on the cognitive abilities of dairy calves.
Past work, the university noted, has shown that feeding calves restricted amounts of milk slows their development, but this study aimed to address what the calves feel, and how hungry they are when under feed restrictions.
These type of studies, Bristol University believes, can help identify farm animal care practices that, when mitigated, lead to improved welfare for many dairy calves.
The experiment
Researchers on the study explained that dairy calves are subjected to reductions in their milk allowance when they are weaned from milk to solid feed.
The researchers expected that the sudden reduction of milk allowance, mimicking what would happen at weaning, would be associated with calves being too hungry to focus on a learning task.
The research team put this hypothesis to the test with a hole-board test adapted for dairy calves in two experiments.
The animals had to remember the location of four rewards (bottles baited with milk) among 15 possible locations (where the remaining bottles were empty).
The test aimed to assess several aspects of cognition including working memory and reference memory, as well as the behavioural flexibility of the calves (their ability to re-learn) when the baited bottle locations are changed.
A 50% reduction in milk allowance (from 12L/day to 6L/day) was chosen because, the team said, it is used in stepdown weaning protocols.
The study explored the impact that a sudden milk restriction had on the calves’ cognitive performance when bait locations were not changed and how it could disrupt their capacity to re-learn after the bottles changed locations.
The reduction in milk allowance was shown to impair the cognitive performance of calves in relation to their focus on the task and their working memory.
Calves with reduced milk allowance struggled to remember where baited bottles were located and they also showed an increase in vocalisations (distressed hunger).
Calves’ cognitive function
The study concluded that feed restriction negatively affected cognitive function, even when baited locations did not change, and that this result is consistent with the idea that calves are distressed by the sudden milk restriction.
One of the researchers on the project, Benjamin Lecorps, said: “Although our results do not provide direct evidence that the drop in cognitive performance was emotionally driven (i.e. that calves felt too hungry to focus), the effect on cognition is consistent with the experience of distressful hunger.
“In addition, milk restriction increased vocalisations, a response commonly associated with negative emotions.
“Together with previous work, our results strengthen the evidence that milk restrictions are associated with negative affective experiences in dairy calves.
“Given the link between cognition and emotions, this type of cognitive approach shows promise in enhancing our understanding of the affective experiences of animals.”
The research team advise that farmers implement ways to mitigate the negative consequences associated with weaning of milk abruptly, such as feeding calves more milk at a younger age and gradually reducing the quantity of milk provided instead of reducing abruptly at weaning.
