Sleep is becoming the next frontier in dairy research, opening discussions and posing more questions regarding its impact on animal productivity, welfare, and ethology.
Researchers Dr. Kathryn Proudfoot and Dr. Emma Ternman recently published a paper on dairy cattle sleep in the Journal of Dairy Science as part of a Special Issue on Dairy Animal Behavior by JDS Communications. Proudfoot is an Associate Professor in the Atlantic Veterinary College at the University of Prince Edward Island, Canada; and Ternman is an Associate Professor at Nord University in Norway.
On a recent episode of the Dairy Digressions Podcast discussing the paper, Proudfoot noted sleep is an essential function of life for all animals. Rodent studies in which the animals were deprived of sleep showed that they eventually died without it.
“We know from human medicine that sleep deprivation is tied to cardiovascular disease, metabolic disease, cancer, and mental health issues,” Proudfoot stated. “We can’t just take this knowledge and apply it to cows, but we do know sleep is important to all animals, so we want to learn more about how it specifically impacts cows.”
Ternman said cows are highly motivated to lie down for about half of the 24 hours in their daily time budgets – roughly 12 hours per day, give or take a couple of hours. But, she noted, those numerous hours of resting are not the same as sleeping. Based on research performed to date, “cows sleep about 3 hours a day, and they do it in short bouts – maybe half an hour at night, and then 15 minutes here, 10 minutes there.”
Researchers also have found that adult cows have 4 “vigilance stages,” or types of sleep, ranging from fully functional wakefulness to rapid eye movement, or “REM” sleep, which is the deepest stage of restfulness. In the two stages in between, they experience a drowsing stage, followed by non-rapid eye movement sleep. Ternman has found that cows can actually ruminate while they are resting in that drowsing zone.
Proudfoot and Ternman theorized that cows don’t sleep heavily, or sleep more, because they are a prey species, so their biological wiring always has them in a state of at least semi-alert for self-protection. But what if you put them in a cushy box stall with zero interruptions? Would they sleep more? “I don’t think so,” answered Ternman. “It’s actually their biology. None of the large herbivores sleep very much. I’ve had research cows in individual pens with plenty of opportunity to sleep, and they didn’t really engage in sleep for a longer period of time.”
But the duo wonders if cows are negatively affected by sleep deprivation below that 3-hour-per-day threshold. Proudfoot noted that in some on-farm settings, cows are exposed to light, noise, and activity 24/7, which she speculates could negatively affect immunity and production potential, as well as their state of well-being.
The tricky part of finding out for sure lies in the ability to actually measure sleep in cows. To date, researchers have utilized polysomnography methods that measure actual brain activity; heart-rate and muscle activity monitoring; accelerometers; and posture monitoring as various ways to evaluate rest and sleep in cows. Some models have achieved greater accuracy by using machine learning models that combine data from multiple methods.
Unfortunately, rumination disrupts activity monitoring. Ternman said in terms of data gathering, it is roughly equivalent to a person grinding their teeth in their sleep. In most human sleep studies, that data is invalid and discarded. Proudfoot also cautioned that, depending on the monitoring method(s) being used, researchers need to be careful to distinguish between “sleep” and “sleep-like behavior” in their observations and conclusions.
They agreed that more automated and less cumbersome methods of recording sleep is needed to further unlock the mysteries of cows and sleep, and eventually lead to conclusions regarding interventions that could improve the quantity and/or quality of sleep for cows if deemed beneficial.
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