Like all mammals, dairy cows are affected by the amount of light they receive each day. Seasonal changes in day length also can have a huge impact in milk production, ranging from 5 lb/cow/day in the northern United States to 8 to 9 lb/day in the south.
Changes in hours of light and day length allow the animal to anticipate changes in her environment before they actually occur, says Kevin Harvatine, a dairy nutrition physiologist with Pennsylvania State University. He spoke this summer at the virtual 4-State Dairy Nutrition and Management Conference.
The seasonal change in available natural light, from 16 to 18 hours of daylight in spring to 8 to 10 hours/day in winter, can have a 5 to 10% effect on milk production, he says. As a result, milk production is highest in April and lowest in September. And if cows are dry in winter, the affect of the shortened days can lead to an increase in mammary tissue growth during the dry period, he says.
“There is no data on how to manage out of this,” Harvatine says. “Managing the photoperiod is probably the best choice.”
As important, cows need a period of darkness as part of their normal, daily, circadian rhythm. Constant light pollution, particularly in large dairies operating around the clock, can be a problem. Even though freestall barns might be dark at night, light pollution from the milking parlor/holding area or lights on skid steers cleaning alleys or pushing up feed can disrupt cows internal clocks.
“I know we are trying to maximize parlor efficiency, but what is 5 to 10% more milk worth?” he asks. “Maybe we can afford to shut down our parlor a couple of hours during the night to get that increase in yield.”
The timing of feed delivery is also critical. Delivering fresh feed stimulates the greatest dry matter intake. But it also can cause slug feeding which in turn may induce rumen upset.
“Make sure feed is available when the cows return from the parlor, but delivering [fresh] feed 2 to 3 hours before or after milking may spread feed intake more across the day,” Harvatine says.
Also be careful with late afternoon and evening feedings. “Night feeding really scares me. It causes slug feeding with huge intake of feed at night and then lower intakes through the rest of the day,” he says. “Early morning feeding may be safer.”