Making and feeding hay and silage is a lot of work. It takes time and money. “Can we get the animals to do some of that work for us?”
Penn State Extension forage specialist Marvin Hall asked attendees at the 2015 Penn State Dairy Cattle Nutrition Workshop. Hall said getting the most from pasture grazing requires a two-pronged approach: optimizing pasture production (the pounds of forage per acre produced) and maximizing the intake from that forage on a per-acre basis.
Managing grazing intake
Dry matter intake (DMI) is affected by pasture height. As pasture height decreases, so does the DMI per bite. To compensate, the cow’s bites per minute need to increase.
“They can’t get enough in their mouths. The cow is working harder and getting less in,” Hall explained. “Their energy balance is in trouble.”
Ideally, cows should be ruminating more and eating less. Cows spend less time eating when they get more DMI per bite. Tall grazing increases rumination.
The DMI consumed on pasture maximizes at about 40 pounds per day, which can occur when forage is 8 to 10 inches tall. When grazing at 2 inches of forage height, DMI is less than 10 pounds per day. But if grazing at the 4-inch height, the DMI will be about 20 pounds per day.
Producers can determine how many pounds of forage are wanted from a given pasture and calculate how tall the plants need to be to produce that amount, then allow the plants to grow to at least that height prior to grazing, Hall said.
Overgrazing pastures isn’t only bad for the cow; it’s bad for the pasture too. Pastures aren’t meant to be grazed to the ground. At 2 inches tall, the plants can’t recover quickly.
“Don’t graze too far down. Leave more out there, and it will grow faster,” Hall said. “We want to keep growth in the really fast zone.”
Soil testing is important. If soil health isn’t optimal, the loss of forage production will be substantially higher than the cost of testing and properly balancing soils.
While the urine and feces of grazing animals add back some of the soil nutrients which were utilized during forage growth, it is only at a rate of 50 to 60 percent, Hall said. If soils are left in a nutrient-deficient state after grazing, plant growth will be compromised.
Soil pH of 6.5 to 8.0 is the target for pasture. Nutrients are not available if the pH is not correct. If the pH is too acidic, the amount of aluminum available will increase and could cause toxicity problems. Legumes fix nitrogen in the soil. Nitrogen fixation will shut down when pH is lowered.
And if potassium is limited, grasses will out-compete legumes. “Soil pH is very crucial in good pasture production,” Hall said.
If legumes are not present in the pasture, nitrogen will need to be added. If a pasture is maintained with 25 to 30 percent of the stand in legumes, the nitrogen levels should be adequate.
Hall said once established, those legumes can contribute 125 to 200 pounds of nitrogen per year, saving on fertilizer costs.
Nitrogen-fixing rhizobia bacteria live in the root nodules of legumes. But nodulation can be impacted by temperature, sun exposure, wet weather, compacted soils and inadequate plant nutrition.
Grazing or cutting pastures will cause the forages to put their energy into regrowth, and the plant will no longer be able to support all of the nitrogen-fixing bacteria, so the amount of nodules will decrease. As some of the roots die back and decompose, nitrogen is released back into the soil and is then available for non-legumes.
“That’s where grasses are getting their nitrogen,” Hall said. If legumes are lacking and a pasture requires additional nitrogen, “put your nitrogen on your better soils,” as that will give “more impact for your dollar.”
Pasture seeding to introduce or re-establish legumes can be accomplished in a variety of ways. While disturbing the soil and broadcasting the seed may be the most conventional approach, other means of seeding legumes can be successful.
Frost seeding is low-input and depends upon no snow coverage, freezing temperatures and a freeze-thaw cycle to deposit seeds in the ground, cover them with soil and leave them to germinate.
Another technique is to seed legumes using no-till methods in late summer, when grasses are slowing their growth. Herbicide-killing grasses, then no-till seeding legumes can also be used. While some farmers seed legumes via animal feeding and digestion, it does not have a high success rate, and distribution is very uneven.
In the spring, there will be rapid pasture growth, which slows down tremendously in summer. How to capture that spring flush and utilize it later when it is needed is one challenge of grazing management.
Delaying any nitrogen application until after the first or second grazing rotation is one option. Increasing the stocking rate so there are more animals to utilize the available forage is another approach. Using a paddock system and then making hay on excess growth is another viable solution.
Extending the grazing season can also be accomplished in a variety of ways. Crop residues can be grazed. Hayfields can be grazed when soil moisture levels are low.
Alternative species such as brassicas or small grains can be planted, thereby increasing the grazing window. Fall-seeding small grains or ryegrass can provide an early spring grazing opportunity.
Increasing the amount of grazing and maximizing the nutrition of pasture forages can decrease feed-related farm expenses. But the effective use of grazing requires more than simply putting animals on pasture. The key to success starts with basic agronomy and finishes with intensive grazing management. PD
Tamara Scully, a freelance writer based in northwestern New Jersey, specializes in agricultural and food system topics.
PHOTO: Overgrazing pastures isn’t only bad for the cow; it’s bad for the pasture too. Photo by PD staff.