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Fact and fiction of dairy pasture nutrition

Tamara Scully for Progressive Dairyman Published on 30 June 2016
Protein is in the top few inches of pasture forage

In today’s total confinement dairies, cows don’t graze. They eat grains, typically fed as a portion of a TMR designed to optimize their intake of protein and energy, provide needed nutrients and maximize milk production.

But the truth is: Cows were built to function without eating grain. Cows didn’t eat grain, at least not until we required them to do so. But they do now.

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“We’ve changed the design,” by breeding cows to produce milk using grain, says Karen Hoffman, resource conservationist – animal science, USDA-NRCS. We’d need to “change the genetics first” to get high-production cows to thrive on a pasture-based diet alone.

Grazing is beneficial to dairy cows and, done correctly, can improve cow health as well as dairy finances. Increasing the dry matter intake (DMI) from pasture saves time and labor on harvesting and storing forages and eliminates some of the manure management concerns that come with keeping cows in the barn, Hoffman says.

Going grazing

Peter Mapstone’s family dairy was a prime example of confinement dairy cows – ones that stayed in the barn and ate “tons of grain,” he says.

Originally pastured, the dairy changed management strategies decades ago when the 60-cow milking herd in Manlius, New York, went to total confinement, began on a high-grain diet and soon had the highest milk production in the county.

But it wasn’t all good. The decrease in the cows’ health and the increase in labor proved confinement dairying was problematic. Returning home from college, Mapstone made some changes; he let the cows back out of the barn.

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“They started to graze and were clean, comfortable and went up in milk,” he says. Herd health “rapidly increased” with no teat issues, and hock bruising – a major concern when in confinement – became a non-issue.

Pastureland Dairy now boasts 300 cows being milked and 300 heifers. They graze on 400 acres of the 1,200-acre farm. They are on pasture from late April until November 1, rotating through paddocks of white clover, orchardgrass and ryegrass.

Balancing pasture nutrition

The goal of grazing is to “try to get as much intake into the cows,” Hoffman says. The minimum required on organic dairies is 30 percent DMI from pasture during the grazing season. But it’s better for the cows, and the bottom line, to do more.

The cows will eat the high-quality forages first, then stop grazing. To keep them eating, they need to be moved to fresh pasture.

“You get much better DMI when you move them frequently,” Hoffman says. “Well-managed pasture that has grasses, clovers [and] forbs is going to be pretty high in protein.”

Such a pasture is often 20 to 30 percent protein. The lactating dairy cow requires about 16.5 percent protein in the diet. But the excess protein, once thought to be of concern, can be readily managed.

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“There are a lot of people who graze high-protein pasture but don’t see issues due to supplementation, breeding and animal management,” Hoffman says.

The key to managing the protein is managing energy. And there really isn’t one right way to do this. The pasture protein can be diluted, or it can be used.

Using the protein requires feeding a small amount of ground corn. The corn provides non-fiber carbohydrates which the rumen microbes utilize, in combination with pasture protein, to make even more microbes.

This also increases milk output. Depending on the production level, a cow would require supplementation between 4 and 10 pounds of corn per day.

Diluting the protein is accomplished by adding fiber. High-quality pasture is very low in fiber. Feeding dry hay or baleage increases the energy to match the protein and “does help on a couple of different levels,” Hoffman says.

Excess degradable protein wastes energy. If the protein isn’t used, it is ultimately excreted as urea. This process requires energy from the animal. But if microbes can combine the excess degradable protein with carbohydrates, it becomes usable by the cows, and energy is not wasted. The rumen needs both protein and energy to function properly.

“Supporting the immune system of the cow is probably the most important thing after maximizing that DMI from pasture,” Hoffman says. “If forages don’t have enough, get minerals into the animals.”

Grain

Many breeds of cows just aren’t going to do as well without any grain – because of their genetics – until we breed them back to grazing. Getting energy into cows can come in the form of small grains, corn silage or cornmeal, or molasses.

It’s fiction that grazing a herd means going no-grain. While there are no-grain, 100 percent grass-fed dairies, obtaining as much DMI from pasture doesn’t have to equate with eliminating all grains, Hoffman says.

Molasses is one way to enhance energy without grain. There is a difference in how energy from molasses, which contributes sugar but no starch to the ration, is utilized in the rumen. Despite this difference, molasses does provide the energy equivalent of corn. It also has a very good mineral profile.

Molasses can be poured on top of hay or haylage – or mixed into the TMR if it doesn’t become too sticky. Three to 4 pounds fed is the upper limit, as molasses is rapidly digested in the rumen, unlike corn silage, which is slowly digested.

Mapstone grows corn silage, haylage and some small grains. The pasture ration consists of haylage, cornmeal and small grains. In winter, when the animals are not grazing, he feeds haylage, corn silage, cornmeal and roasted soybeans. He only has to purchase the soybeans, utilizing homegrown feeds for the rest of the ration.

Grazing plan

Should dairy cows be grazing tall or grazing short? Tall-grass grazing has grown in popularity but limits DMI, Hoffman says. This is because the cows will stop at about 8 inches in height and “pick and poke” around the stalks.

If grazed short, at 6 to 8 inches, the cow can wrap her tongue around the base and get all of the plant. They eat faster this way.

Protein is in the top few inches of pasture forage, and fiber is in the remainder. Energy, too, is in the top growth. Nutrients are equivalent throughout.

When grazed at a height of 10 to 12 inches, a 1,400-pound cow’s daily milk production from grazing tall forages would be about 65 to 70 pounds. This would increase to 90 to 100 pounds when grazing at shorter heights of 6 to 8 inches.

The rest period in each field between grazing is important, as pasture growth needs to regenerate. Rotating animals frequently, using a grazing chart, perimeter fencing and subdivided paddocks, helps to get the most pasture intake into the cows while preventing overgrazing.

Bred for grass

Although Mapstone originally grazed Holsteins and had positive, immediate results, he has been breeding Holsteins to Jerseys and getting a better grazing animal. Holsteins come back to the barn if the weather gets hot.

The crosses will graze all day in the heat, produce about the same amount of milk as the Holsteins and have fewer health problems in an animal half the size of the Holstein. They also generate higher milk components, so component pricing is another positive, he says.

“Having a cow that comes in and gives you no trouble at all makes a lot of sense,” Mapstone says of his crossbreds. “It’s a lot easier to get the milk production from those cows with cross-breeding.”

The truth is: Pasture grazing can work well on a dairy, even when milk production is an issue. Obtaining the maximum DMI from pasture and supplementing for energy allows producers to make the most of their resources with the least amount of labor and still keep production high. With a bit of effort, managed rotational grazing can bring big benefits to the cows, the farmer and the dairy’s finances.  PD

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

PHOTO: Protein is in the top few inches of pasture forage, and fiber is in the remainder. Energy, too, is in the top growth. Nutrients are equivalent throughout. Photo by Mike Dixon.

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