Dairy grazing isn’t a simple science. Putting a milking herd on pasture involves more than providing access to grass. It’s a multifaceted system that involves the health and productivity of animals, plants and soil. Dairy herd grazing requires knowledge not only of the dietary needs of milk-producing cows but also of plant growth and soil health. These factors all work together and influence one another. Since weather isn’t a stagnant or even highly predictable factor, and plants don’t grow the same in all seasons or weather conditions, grazing management requires flexibility and backup plans.
"It’s really necessary that we have that integrated approach,” to dairy grazing, said Dr. Dennis Hancock, U.S. Dairy Forage Research Center (DFRC) director, in a 2021 presentation. Hancock explained that the research center, located in Wisconsin, focuses on animal and cell physiology, on dairy forage production and use in dairy feeding systems, and on decreasing the environmental footprint of U.S. dairy farms. Other USDA Agricultural Research Service (ARS) centers – in Pennsylvania, Minnesota and Tennessee – have complementary focuses.
Grazing pasture to produce milk requires a basic understanding of the perennial grasses and pasture legumes that grow well in the region, as well as their yield and digestibility. Each species of grass – and even varieties of the same species – has differences in the percentages of the plant that is composed of cell contents and of cell wall. Cell contents are readily digestible; it’s cell walls that are fibrous and of questionable digestibility. Neutral detergent fiber (NDF) measures the percentage of fiber in a plant, while neutral detergent fiber digestibility (NDFd) measures the percentage of that fiber which is digestible.
While grasses tend to consist of 50% fiber, a large portion of that fiber is digestible – about 75%. Legumes have less fiber overall, with a 35% fiber content, but the fiber they do have is only 40% digestible. Overall, the percentage of NDFd in grasses hovers around 37.5%, but for legumes it is only 14%. This is because there are more “linkages” in the fiber of legumes, while that of grasses is stringy in shape, Hancock said.
Of common pasture grasses – such as meadow fescue, orchardgrass and tall fescue – NDF is typically between 40% and 50%, while NDFd is about 70% to 80%. Meadow fescue has lower NDF but higher NDFd compared to the others, making it more digestible and a good forage option, he said.
Seasonal grass yields, as well as cow productivity on that grass, are other important considerations for grazing dairy cows. Hancock shared research that has shown that meadow fescue and orchardgrass yield more dry matter per acre than does improved tall fescue during spring and fall seasons in the Midwest region of the U.S.
Milk production requires yield and digestibility. Researchers have measured milk production in pounds of milk per acre of forage for meadow fescue, orchardgrass and improved tall fescue. This data shows not only seasonal variations in milk production for each species but also between species.
“Species difference affects fiber digestibility. Varieties can matter, too,” he said.
It’s important for dairy graziers to “maintain a competitive level of productivity,” and “one of those ways of doing that is to improve our pastures, to make sure we are providing good nutrition for our animals and being very efficient with our overall scheme,” Hancock said.
Pasture renovation research data has revealed that after the first year, pastures renovated with newer forages chosen for quality, productivity and suitability to the climate – in this case, the meadow fescue, improved tall fescue and orchardgrass, which grow well in the Midwest and have suitable digestibility – initially yield more dry matter than non-renovated existing pastures when managed under the same conditions for grazing. While renovated pastures increased forage yield about 20% from the non-renovated sections in year two and three, production dropped to about half of that increase in the third year. Interestingly, a natural revision back to the pre-existing mix of pasture grasses was seen after three years.
Grazing management impacts the quality and quantity of pasture forages. Grazing grasses at the wrong time, or grazing them too short are common reasons productivity is sacrificed. Research on the height of residual grass after grazing has shown that it does matter how much residual is left on the pasture.
Whether grazing tall, more mature grass stands at 20 inches in height, or grazing at 12 inches tall, grazing to a 2-inch residual causes bare soil, which can promote weed growth, erosion and runoff. Leaving 4 inches of residual allows the plant to grow from photosynthesis rather than from carbon reserves in its roots and results in more root growth and more tillering of the plant.
Managing forages means always having a back-up plan. Weather can always cause production to change from the norm. Whether it's due to drought, too much rain or unseasonable temperatures, pasture forages aren’t always ready for grazing just because the animals need to graze it. Research shows that grazing management must change as the seasons do.
Grazing at 6 inches in height – whether early spring, midsummer or late fall – when compared to waiting on the same pastures for a recovery of 14 inches, has implications. If shorter recovery periods happen in May, a yield loss of 400 pounds for the month was seen, but no loss occurred when yield was measured throughout the grazing season. When the recovery period was shortened during July, there was a loss of 200 pounds of forage for the month, and 600 pounds total for the grazing season. If the grass was grazed at 6 inches in October, there was no loss for the month and no overall loss of forage yield for the entire season.
“You really need to have an emergency forage option in July. A good contingency plan would be to consider some warm-season annuals,” such as brown midrib sorghum, pearl millet or a brown midrib sorghum-sudangrass cross. “Any of these would work quite well,” Hancock said, and each has a role to play.
Baleage cuttings on these annuals are best done on the first flush of growth, particularly with the sorghum-sudangrass, as it grows rapidly and will get ahead of the cows quickly. Pearl millet, where suitable to grow, maximizes mid- and late-summer resiliency.
Planting fall-grown oats is a good option for season extension with stockpiling forages. Stockpiled annual forages don’t regrow, so there is no need to back fence the herd – just keep moving them forward. Dry years, however, can be challenging for fall annuals.
Managed grazing offers dairy farmers the opportunity to decrease the negative environmental impacts of dairy farming while promoting animal health, Hancock said. Proper grazing management of the dairy herd can decrease nitrate leaching when compared to confinement dairy farming. It can lessen ammonia volatilization and phosphorus runoff. While some increase in methane emissions has been seen in grazing cows compared to confined ones, that effect can potentially be mitigated by increasing forage digestibility. After an initial lag phase, soil organic matter has been shown to increase substantially in “an amazing turnaround” after implementing grazing.
“Pasture-based dairy really has great opportunity for carbon sequestration, and maybe the complete life cycle analysis really hasn’t fully incorporated some of that information about soil organic matter,” he said.
Understanding of the principles of pasture management is the name of the game in dairy grazing. Improving pasture persistence and quality in dairy grazing systems, improving forage varieties and quantifying qualities of existing forages, identifying grazing’s influence on plant quality, understanding the impact of residual height and grazing timing on forage quality and yield, and extending the season with annuals are all part of the ongoing research focus at the DFRC.
The aim of the grazing research is to create productive, resilient dairy farms that have a positive impact on the environment. The overall goal, Hancock said, is the development of “a whole-farm system of best management practices to try to mitigate the environmental impact of dairy.”
For more information, visit the U.S. Dairy Forage Research Center website.