Hungry animals sacrifice play to prioritize finding food
At the University of Bristol, researchers have uncovered something quietly profound about the inner lives of young dairy calves: hunger does not merely empty the stomach — it narrows the world. A study published in Scientific Reports found that calves receiving double the standard milk ration played freely and chose movement over reward-seeking, while those on conventional rations became sharper, faster, and more driven — but lost access to the simple joy of play. The findings invite us to reconsider what it truly means to feed an animal well, and whether survival and flourishing are as close together as we have long assumed.
- Standard dairy farm feeding rations — just six liters of milk daily — may be quietly extinguishing one of the most natural behaviors a young animal can express: play.
- Underfed calves outperformed their well-fed peers in maze tasks, completing them faster and with sharper recall, but the cost was a near-total suppression of curiosity and social engagement.
- Even after sixteen hours without milk — a routine gap on twice-daily feeding schedules — calves raised on double rations still chose play over chasing a food reward, revealing how deeply satiety reshapes motivation.
- Researchers are now pressing the industry to treat increased milk allowances not as indulgence but as a welfare intervention, one that could restore behavioral health alongside physical health.
- The study lands as farms face mounting pressure to move beyond minimum nutritional standards and reckon with what animals actually need to thrive rather than merely survive.
Researchers at the University of Bristol began with a deceptively simple question: what happens to a young animal's priorities when it isn't quite hungry enough? The answer, published in Scientific Reports, challenges some of the most basic assumptions behind how dairy farms feed their calves.
The study followed two groups of ten calves over three weeks. One group received twelve liters of milk daily — double the conventional amount. The other received the standard six-liter ration. Both groups were then tested in a maze where milk served as the reward, allowing researchers to track how hunger shaped memory, motivation, and behavior.
The contrast was stark. Calves on the standard ration completed the maze faster and remembered it better — they were sharper, more driven. But they barely played. The well-fed calves moved through the maze with less urgency and less focus on the reward. What they did instead was play: the spontaneous, exploratory behavior that young animals engage in when survival is not the immediate concern.
Lead author Jillian Hendricks described the finding as a window into a fundamental motivational trade-off. Hunger doesn't simply make animals want food more — it suppresses everything else: curiosity, social engagement, the pleasure of movement. What made the result more striking was that both groups were tested after a sixteen-hour fast, a normal interval on farms that feed calves twice daily. Even after going most of a day without milk, the well-fed calves still chose play over the maze task.
Co-author Dr. Ben Lecorps drew a direct line to farm welfare policy. The standard six-liter ration may meet calves' basic caloric needs, he suggested, but it may simultaneously be suppressing behaviors that signal psychological health. Increasing milk allowances, the researchers argue, could serve a dual purpose — easing the physiological stress of hunger while restoring the behavioral freedom that comes with it. Play, the study implies, is not a luxury. It is what an animal does when it is no longer consumed by the need to find its next meal.
A team of researchers at the University of Bristol set out to answer a deceptively simple question: what happens to a young animal's priorities when it isn't quite hungry enough? The answer, published in Scientific Reports, upends some basic assumptions about how dairy farms feed their calves.
The study compared two groups of ten calves over three weeks. One group received twelve liters of milk daily—double the standard amount given on most dairy farms. The other received six liters, the conventional ration. Both groups were then placed in a maze and tasked with finding milk as a reward. The researchers wanted to see how motivation and memory shifted based on how well-fed the animals were.
What emerged was stark. The underfed calves—those on the standard six-liter allowance—completed the maze tasks faster and showed sharper recall. They were, in effect, more driven. But they paid a price: they barely played. The well-fed calves, by contrast, moved through the maze with less urgency. They were slower, less focused on the milk reward. Instead, they played. They engaged in the kind of behavior that young animals do when survival isn't the immediate concern.
Jillian Hendricks, the study's lead author, framed the finding in terms of a fundamental trade-off. Hungry animals, she explained, sacrifice play to prioritize food. It's not a choice they make consciously—it's how their motivation system works. Hunger suppresses other competing drives: curiosity, social engagement, the simple pleasure of movement and interaction. The research opens a window onto how this hierarchy of needs operates in farm animals, creatures that are often denied the chance to express behaviors beyond eating and basic maintenance.
What made the finding more striking was the timing. Both groups were tested after a sixteen-hour fast—a normal interval on farms that feed calves twice daily, at eight in the morning and four in the afternoon. Even after going without milk for most of a day, the well-fed calves still chose play over the maze task. "Despite this long period without milk, calves fed more still prioritised playing," Dr. Ben Lecorps, a study co-author, noted. "This tells us a lot about how much play matters for them."
For dairy farmers, the implications are practical. The standard milk allowance—six liters—may be meeting calves' basic nutritional needs, but it may also be suppressing behaviors that matter for their wellbeing. Lecorps suggested that increasing milk allowances could serve a dual purpose: not only would it reduce the physiological stress of hunger, but it would also allow calves to express natural behaviors that indicate psychological health. Play, in other words, is not a luxury. It's a marker of an animal that isn't constantly driven by the need to find its next meal.
The research is among the first to directly measure this trade-off in farm animals, and it raises questions about what we mean by adequate feeding. Meeting an animal's caloric requirements may not be the same as meeting its behavioral needs. As farms face growing pressure to improve animal welfare, studies like this one suggest that the answer may not be complicated: feed them more, and watch what they do with the freedom that follows.
Notable Quotes
The study is among the first to show that hungry animals will trade-off play to prioritise finding food, expanding our understanding of how hunger suppresses other competing motivations and emotions like play opportunities.— Jillian Hendricks, lead author
The standard milk allowance for calves may disrupt other important behaviours which indicate they may experience hunger. Feeding calves more may not only suppress hunger but also contribute to the expression of other important behaviours like play.— Dr. Ben Lecorps, study co-author
The Hearth Conversation Another angle on the story
So the calves that were hungrier actually performed better at the maze task. That seems counterintuitive—doesn't hunger usually impair cognition?
It does in some contexts, but here the hunger created a kind of laser focus. The underfed calves were motivated. They needed that milk, so they learned the maze faster and remembered it better. It's not that their brains worked better—it's that their entire system was oriented toward one goal.
And the well-fed calves just... didn't care about the milk?
Not exactly. They could do the task. But they had other things they wanted to do more. Play. Movement. Interaction. When you're not desperate, you have the luxury of choosing what interests you.
The study mentions they all went sixteen hours without food before testing. That's a long fast. Why did that matter?
Because it shows that even under stress—even when all the calves were hungry—the well-fed group still prioritized play. That suggests play isn't a frivolous behavior they indulge when everything is perfect. It's something they actively value, something that matters enough to choose even when they're uncomfortable.
What does this mean for how farms actually operate?
It suggests the standard feeding amount might be creating a kind of chronic low-level hunger that keeps calves in survival mode. If you fed them more, you wouldn't just reduce their hunger—you'd give them the mental space to be calves, not just eating machines.
Is there a risk that feeding more would just make them lazy or unhealthy?
The research doesn't suggest that. The well-fed calves played more, but they weren't lethargic. They were more engaged with their environment, more active in ways that matter for development. It's the opposite of laziness.