A cow’s body clock dictates her milk production, components and how she eats.
I once worked with a dairyman who would force his cows up several times during the day and night to come to the feed bunk and eat. He knew that more feed intake meant more milk.
But cows have daily routines just like we do. Upsetting these routines can have consequences. Cows are influenced by circadian patterns -- body clocks, if you will -- and any disruptions may affect cow health and production.
Cow behavior is influenced by a master clock, which is controlled by day and night -- light and dark. They also have peripheral clocks that are affected by environmental clues and feeding times.
Photoperiod has a huge influence on production. Milk, fat and protein increase with increasing day length. It’s not just the amount of daylight, but the change in day length that affects production. Hence, the spring milk flush as day length rapidly increases.
Dr. Kevin Harvatine of Penn State University has been studying circadian patterns of production in cows. He shows that cows consistently produce more milk from the morning milking than the evening milking. This response is consistent for both 2- and 3-time per-day milkings. The difference between morning and evening can be over 4 lb. per cow per day. Milk composition also varies with time of day. Body temperature also follows circadian rhythms, as does feed intake and rate of feed intake. Even when feeding a TMR, starch intake varies greatly during the day due to intake variability. It’s usually higher in the morning just after milking. Thus, rumen pH can also vary, according to Dr. Harvatine, with daily intake variability.
What does all this have to do with night feeding? Cows like their routines. They like having fresh feed available when they return from the parlor. They like to eat their fill and then lie down and rest and ruminate. When we feed a higher portion of their daily feed at night during hot weather, cows tend to slug feed (a common term for eating a lot of feed quickly). This is evidenced by Kevin’s data showing a high insulin response to a high rate of intake when feed is put out at night. It may be that cows want to eat quickly so they can get back to their routine – resting at night. I’ve always recommended feeding a greater portion of the daily intake at night during the summer. Cows eat more when it’s cooler. Dr. Harvatine’s studies indicate that there is more to it.
We need to keep the cow’s body clock in mind -- maybe a higher forage concentration in the evening TMR to counteract the greater rate of intake and reduce the potential for acidosis.