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Feed specialist addresses grazing dairy herd nutrition

Tamara Scully Published on 18 April 2014

A dairy herd grazes in Vermont.

Dairy farmer Mike Thresher is also a dairy specialist with Morrison’s Custom Feeds. Thresher has been working with both organic and conventional dairy producers in Vermont for more than a decade.



Thresher has found that more dairy farmers are becoming interested in grazing – and that myths and missteps abound when opting to graze the herd.

“Feed changes when on pasture,” Thresher said at the 18th Annual Vermont Grazing Conference. Rations need to be adjusted to complement the actual protein, energy and dry matter being consumed in the field.

It isn’t as simple as letting the cows graze and decreasing the amount of grain mix. The grain mix will have to change based on the amount and quality of the consumed pasture forage.

Pasture forage isn’t a constant, and its quality and availability changes quickly. Balancing the ration starts with a good understanding of what the cows are actually consuming.

“Not knowing what they are going to eat,” is a major issue with grazing, Thresher said. “Forage quality and availability are the two limiting factors. You’ve really got to go out and look around and see what the cows are eating.”


If you are assuming the cows are eating all the pasture forage you see, your dry matter intake (DMI) will be “way off,” Thresher said. If the DMI is skewed, herd production and health will decrease. And cows are not going to consume everything in a pasture. The amount of forage actually consumed – the utilized forage – is what is important for calculating needed pasture supplementation.

“Cows don’t graze a sample,” Thresher said. “How much are they eating? What is left when they leave?”

Green pastures themselves don’t indicate that the cows actually have the food they need for optimal milk production. Lush spring growth, for example, looks plentiful but is low in protein, typically analyzing at 14 to 16 percent protein. If it’s been very rainy, the energy content of forages will decrease. Milk urea nitrogen will increase if there is protein but low energy, he said.

Balancing pasture nutrition
Thresher determines what is needed in a grain mix for a grazing herd by going out and observing what the cows have actually consumed in the pasture. Wet spots can mean under-grazed forages, as extra moisture promotes decay, and the cows won’t graze these areas at all.

After observing what has been eaten in the paddock, he compares that to what is available in the next paddocks to determine the dry matter intake, protein and energy that will be consumed.

“In a pasture where there is not sufficient dry matter intake, both energy and protein end up being deficient, but mostly the energy is lacking,” he said. Pasture that “looks like a golf green” when the cows are moved indicates that there was not sufficient dry matter intake.


Paddock sizes will need to change as the availability of forage decreases during the hot summer months. The pasture needs a longer resting period, and fresh pasture should be added in to the rotation in order to maintain milk production.

Producers should also consider increasing fed grain if bulk tank weights drop, in order to keep up milk production while grazing, Thresher said, as the cost of the grain will probably be outweighed by the added gain from the continued higher levels of milk production.

The long-term goal for grazing dairies would be to increase forage quality and reduce the amount of grain needed each season by grazing smarter.

“Over-grazing is one of the biggest things I see every year. The quality of the forage from an over-grazed pasture is lower as the plants are stressed and not growing normally.

I see this quite often in the summertime, usually around July 10. This is very evident from mid-July and on as I see a gradual decrease in milk production. The key to milk production is dry matter intake,” Thresher stated.

Participants in a pasture walk examine the forages available in a pasture.

Adding grains is the easiest way to increase energy levels, often lacking in pasture. Corn silage is a good choice. Corn meal provides the highest energy level. Barley, oats, wheat or small-grain silage are other options, as are beet pulp and molasses.

“The best supplements for a no-grain approach would be to have part of the grazing include grazing an annual crop such as oats, annual ryegrasses, triticale, sorghum-sudan or millet,” Thresher said.

Quality pasture
“They can get all the protein from pasture,” Thresher said. But typical pastures are deficient in energy. Grazing cows need more energy than confined animals, as they expend energy walking, a factor that is often overlooked.

A high-quality, well-managed pasture can offer net energy lactation of 0.7 to 0.8 Mcals, along with protein levels of 22 percent or more. These higher levels are for the best-quality pasture, which can also offer 40 pounds of dry matter if grazing 10 hours per day, according to Thresher.

Farmers continually build the soil through proper grazing management, Thresher said. Adding manure applications to pastures, when done properly when rain is guaranteed, can help to increase the protein levels and increase the forage density of pasture and help sustain it throughout the season, he said.

He’s also seen some producers use fish fertilizer, resulting in higher protein levels and a bit more energy than neighbors, but there is a cost associated with that, which needs to be weighed against the benefit. Rest and recovery periods of the pasture are very important in increasing pasture nutrition.

Good pasture management includes moving the cows to fresh grass twice per day. Thresher also recommends clipping pastures two or three times each season and introducing new seeds into the pasture, such as red clover, ryegrasses and annual grains.

“On average, the diet I like to see has an energy level around 0.75 Mcals of energy,” Thresher said. “The energy needs will vary based on milk production goals.”

As dairy producers opt to increase the amount of grazing being done by the milking herd, the amount of grains being fed has to be adjusted to reflect the actual amount of protein and energy being consumed in grazing. If these factors are not accurately calculated, the diet will not be balanced, resulting in herd health concerns and loss in milk production.

“No matter if a cow is grazing or totally confined, her milk production will be largely based on the total amount of dry matter consumed,” Thresher said.

Knowing the DMI, protein and energy levels actually being consumed from pasture, and realizing these are not static figures but ones which change based on forage conditions, is the first step to providing an optimal diet for the grazing dairy herd. PD

Tamara Scully is a freelance writer based in Columbia, New Jersey.

Mike Thresher can be reached by email or by calling (802) 684-2130.

TOP: A dairy herd grazes in Vermont.

MIDDLE: Participants in a pasture walk examine the forages available in a pasture. Photos courtesy of Jenn Colby, Pasture Coordinator, University of Vermont Center for Sustainable Agriculture.