Cows want to do certain things at certain times, and there’s a reason for that. Cows naturally try to synchronize rhythms so that milk synthesis will occur when nutrients are available.

“All physiological function follows a 24-hour cycle,” Dr. Kevin Harvatine of Penn State University said at the 2015 Penn State Dairy Cattle Nutrition Conference, held last November. The 24-hour cycle of the circadian rhythm “allows the body to anticipate changes before they occur.”

This circadian rhythm causes “daily patterns of intake and milk synthesis” in dairy cows, Harvatine said. Nutrient absorption follows daily patterns, too, so that the body “delivers nutrients to the mammary gland as they are needed.”

If the circadian rhythm isn’t followed, nutrients “won’t efficiently be transferred to milk,” he said. Increasing milk nutrients means matching the herd’s daily activity patterns to the mammary gland cycle.

Rhythm functioning

The circadian rhythm keeps its beat by following a variety of cues. Light, hormones and even the seasons naturally cause changes in daily patterns. The brain maintains a 24-hour clock, which is “set” by sunrise and light. Hormonal signals are sent from the brain to the peripheral tissues. These tissues also keep track of time and maintain a 24-hour rhythm. But unlike the brain, their response is more heavily influenced by factors other than light.

“These peripheral clocks are also responsive to a wide range of other functions,” such as feeding time and milking time, as well as to light, Harvatine said.

The change in seasons impacts milk composition. A repeated 12-month pattern where milk fat and protein consistently vary throughout the year, no matter the weather pattern or region, has been observed. The same seasonal fluctuations occur across regions of the U.S. through varying weather patterns.

“It’s way too consistent to be heat stress,” Harvatine said of the seasonal pattern. Instead, it correlates with day length.

Intake, too, changes throughout the day. The digestive system will “ramp up” prior to the time a meal is anticipated.

Cows naturally prefer to eat in the afternoon. This makes sense, as on pasture, grasses contain more sugar content in the afternoon, due to photosynthesis. Cows naturally will seek the increased nutritional values, so they graze in the afternoon.

Cows cannot eat and ruminate at the same time. Once the sun goes down, they want to sleep. Cows do most of their ruminating at night. Rumination follows the circadian rhythm, and rumination counts must be done at a consistent time to be accurate, Harvatine said.

Managing rhythm

“Feed delivery is a strong stimulus to intake. Fresh feed is a strong stimulus, but the response to the stimulus depends on when you feed,” Harvatine said.

There are differences in metabolic functioning throughout the day. Cows fed in the morning do not show any spikes in insulin levels. But if fed at night, there is a very large insulin response. Even if fed at night, cows will eat during the day. But they won’t eat as much as they otherwise would at this time.

“Cows are eating in the afternoon not because the feed is fresh, but because that is when they want to eat,” Harvatine said.

Feeding two or three hours before or after milking may help to spread intake across the day. After milking, cows want to eat a lot. Feeding at night does not increase daily intake, and cows don’t want to eat at night.

Milk yield and composition changes naturally throughout the day. Within any given dairy, milk yield and composition will differ depending on the time of milking. Milking rhythms, in turn, depend on how often the cows are milked each day. These milking rhythms can be altered by changing feeding times.

“Daily pattern intakes affect the nutrients available in the blood, which is also impacting nutrients available to the mammary gland,” Harvatine said.

Cows have different metabolic capacities throughout the day. The rumen follows a circadian rhythm, too. Cows don’t eat at the same rate throughout the day, so there are differences in the starch levels entering the rumen depending on when the cow is eating. There is a three-fold difference in the amount of starch available for rumen microbes throughout the day.

The same TMR ration will be digested differently depending on when it is fed. Using multiple rations may better impact rumen functioning, Harvatine said. These TMR changes don’t have to be too complex, but can have a positive impact.

Artificial lighting is a serious concern, particularly as large dairies implement night shifts. Having continual light is extremely confusing to circadian rhythms – both for humans and for cows.

“I think people are losing a lot of potential if they are not using six-hour dark periods,” Harvatine said. “Providing darkness is really important.”

Paying attention to the natural circadian rhythms of the dairy herd results in increased milk yield and nutrients. Making management changes so that the daily routine is realigned with the circadian rhythm can be prudent.

“Cows are pretty robust. But there are things that we can do in our management that can create some hurdles,” Harvatine said.  PD

Tamara Scully, a freelance writer based in northwestern New Jersey, specializes in agricultural and food systems topics.

PHOTO: Staff photo.

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