When calves don't get enough milk (which happens almost everywhere in the dairy industry), they experience negative physical and mental effects. The researchers who carried out the study hope this can motivate farmers to offer better conditions for calves and their mothers.
Like humans, cows only produce milk after they are pregnant. This means that dairy cows must give birth to at least one calf per year to keep on producing milk, so they're constantly artificially inseminated for this purpose -- often after just 2-3 months of giving birth. But the goal of the practice is to take as much milk as possible for sale, so calves receive much less milk than they normally require.
In practice, calves receive around half of the required amount of milk and are quickly switched to solid feed (or sold for slaughter). Previous research has already shown that this slows down their development and affects their health, but there hasn't been much research into what calves feel.
To study this, researchers from the University of Bristol used a test where calves have to remember the location of 4 milk-filled bottles among 15 bottles. They wanted to see whether a sudden milk restriction (halving the milk intake from 12 to 6 liters per day) would affect their capacity to remember where the rewards are and whether it would disrupt the capacity to relearn the locations after changing locations of the bottles.
In all cases, the milk restriction affected the calves' ability to learn and remember, a result that is consistent with them being too hungry to focus. Although the researchers stop short of claiming that, and simply say that the effect on cognition is consistent with the negative experience of ‘feeling’ hunger, it's still a concerning animal welfare issue.
"Our results show that calves’ ability to focus is seriously reduced when their milk allowance is suddenly decreased suggesting that they most likely experience negative emotions associated with hunger.
"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.
Researchers hope that this type of study will push for better animal welfare standards.
"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."
Journal Reference: 'Hunger affects cognitive performance of dairy calves' by Benjamin Lecorps, Raphaela E. Woodroffe, Marina A.G. von Keyserlingk and Daniel M. Weary in Royal Society Biology Letters [open access]