An associate professor in nutritional physiology at Penn State University, Harvatine has been studying the relationship between natural patterns in the environment (seasonal changes, time of day) and production of milk, looking at both volume and components.
Daily rhythms coordinate the animal’s metabolism with changes across the day. Most processes in the body follow a 24-hour cycle, such as sleeping then waking. Cows follow a similar daily pattern in milk synthesis, which is why morning milk differs in components to the later-day milking.
Cows respond to environmental cues, such as light versus darkness. Thus, the tissues within their body have a daily pattern in response to daylight and nighttime. Harvantine shared the known impact of photoperiod on milk yield, crediting a 5%-10% increase in production to extending light per day in a freestall barn from eight to 10 hours, to 16 to 18 hours.
However, further research suggests the opposite is true for dry cows.
“A short photoperiod during the dry period increases milk yield in the next lactation,” Harvatine said.
“We are leaving a lot of milk and a lot of money on the table by not having proper administration of photoperiod light and darkness,” Harvatine said. “I think managing photoperiod is your best course of action. My recommendation would be to have good light control, have a dark period and have long days.”
Just as cows’ rhythms change throughout the day, they also shift as the hours of daylight and temperatures adjust with the seasons. Milkfat follows a similar pattern.
Harvatine described it as a “perfect repeating pattern” of seasonal milkfat and protein fluctuation. Both components tend to peak around Jan. 1, and then hit their lowest point around July 1, each year. Despite the concurrence of lowest milkfat and peak heat stress in July, Harvatine said research does not necessarily suggest a connection between the two.
“We have a seasonal pattern, and then we have heat stress. We need to disconnect those and manage them independently,” he said.
One of the most critical management areas is feed timing and delivery. Cows exposed to heat stress are more likely to slug feed, which Harvatine said is linked to higher incidence of milkfat depression. The goal is to stabilize the amount of feed entering the rumen throughout the day.
“Feed delivery is a strong stimulus,” Harvatine said. “It’s the biggest bullet we have in our gun.”
Bringing fresh feed to the cow is the strongest stimulus for a cow to get up and eat, and the timing of this stimulation is particularly important during heat stress. Make sure fresh feed is available when cows return from the parlor, he suggested. However, avoid timing delivery with when cows are being milked.
“I really don’t like the idea of delivering fresh feed when cows are away from the parlor, because this is your big opportunity to stimulate intake and you are wasting it because they were going to eat anyway,” he said.
As an alternative, deliver feed two to three hours before or after milking to help spread intakes across the day. Harvatine also discouraged late-day and evening feeding during times of heat stress. Avoid feed delivery after 4 p.m., as that may encourage slug feeding. Feeding different diets across the day may help stabilize intakes as well, such as stimulating the high group with an extra feed delivery.
Understanding these daily and seasonal patterns of dairy cows and adjusting management practices to capitalize on them has the potential to influence milk production.
“We have our light-dark cycles, our milking times and feeding times. This all has an impact on when the cow is eating and getting nutrients to the mammary gland,” Harvatine concluded, “and I think it’s impacting … how much milk she is making.” 
-
Peggy Coffeen
- Editor
- Progressive Dairy
- Email Peggy Coffeen
