When researchers designed what was essentially a milk-based memory game for dairy calves, some approached the challenge with focus and efficiency, quickly learning where milk rewards were hidden around an arena. Others seemed to have something else on their minds.
Instead of immediately searching for milk, some calves spent their time running, jumping and bucking around the test arena.
The findings, published in Scientific Reports, offer an intriguing look at how feeding level may influence calf behavior, motivation and welfare. They also highlight an important challenge in animal cognition research: sometimes what appears to be a difference in learning may actually be a difference in what animals value most.
Researchers Thought More Milk Would Improve Calf Learning
Led by Ben Lecorps, senior researcher at the University of Bristol Veterinary School, researchers compared calves fed a standard milk allowance of 6 L/day with calves receiving up to 12 L/day.
“We expected that calves who were given more milk would show better cognitive performance compared to standard-fed calves,” Lecorps explains.
Instead, the opposite appeared to happen.
“It became quickly obvious that they were more motivated to play than they were to work for food,” he says. “This was unexpected because regardless of feeding treatment, all calves had a 16-hour gap with respect to their last meal, so we thought they would all prioritize finding food.”
Scientists Tested Memory and Learning in Dairy Calves
The study involved 20 preweaned calves housed in pairs. Researchers used a hole-board test, a cognitive task commonly used to evaluate spatial learning and memory.
Inside a 5-by-3-meter arena, calves were presented with 15 buckets mounted along the walls. Four contained milk rewards. Over repeated trials, the animals had to learn and remember which locations contained milk.
Researchers measured both working memory, which is a calf’s ability to remember which buckets had already been visited during a trial, and reference memory, which is its ability to remember reward locations between trials.
The reward locations remained the same for 14 trials before being changed for a six-trial relearning phase.
Feed-Restricted Calves Outperformed Better-Fed Calves
The restricted-fed calves generally performed better in the test. They showed stronger working and reference memory scores, reached the first bucket more quickly, completed trials faster and located more rewarded buckets over time.
At first glance, the findings might suggest milk restriction improves cognition. Lecorps cautions against that interpretation.
“It is not possible to answer this question with absolute certainty,” Lecorps said when asked whether the restricted calves were cognitively superior. “However, we think our results are best explained by feed-restricted calves being more motivated to find milk than enhanced-fed ones, which were prioritizing play at the expense of finding food.”
In other words, the restricted calves may not have been smarter. They may simply have been more focused on the reward.
That distinction is important because cognitive performance is influenced by motivation. An animal that is highly motivated to obtain a food reward may outperform a less motivated animal even if their underlying cognitive abilities are similar.
Well-Fed Calves Preferred Play Over Searching for Milk
The study’s most memorable finding may be what the better-fed calves did instead of searching for milk.
“Enhanced-fed calves really prioritized playing over finding food,” Lecorps says. “Often, they would spend the first few minutes jumping and bucking, and then decide to make a start at finding the milk buckets, but with much less urgency than feed-restricted ones.”
The test arena was substantially larger than the calves’ normal living space, giving them an opportunity to express play behaviors that may have been limited in their home environment.
What Play Behavior Reveals About Calf Welfare
Play is often viewed as a pleasant extra in young animals, but growing evidence suggests it plays an important role in development.
“Young mammals are extremely motivated to play because it is essential for their motor and cognitive development,” Lecorps says. “It helps them build skills and competencies that help them cope with future challenges.”
Play is also commonly used as a welfare indicator because animals frequently reduce play behavior when experiencing pain, illness, stress or hunger. The restricted-fed calves consistently played less throughout the study, suggesting hunger may have shifted their priorities toward food acquisition and away from other important behaviors.
Implications for Milk Feeding Programs and Calf Housing
This study adds another perspective to ongoing discussions around calf-feeding strategies and housing systems.
“Our results highlight that calves fed more milk choose to prioritize play over finding food,” Lecorps says. “Importantly this does not mean that milk is no longer important for them, but that higher quantities of milk allow them to seize opportunities for play behaviors.”
He believes the findings point to two practical considerations. First, producers and veterinarians should consider the full range of benefits associated with feeding higher milk allowances. Second, calf housing systems should allow animals enough space and social opportunity to express play behavior.
“The key takeaway, I think, is that there are clear benefits in feeding calves more milk and in housing them in bigger pens with peers, so as to favor play behaviors,” Lecorps says.
Researchers originally set out to study cognition. Instead, they uncovered something equally revealing: When calves are less constrained by hunger, they may decide there are more enjoyable things to do than chase milk buckets.
