There’s a lot of talk these days about different grazing systems. Mob grazing, management intensive grazing (MIG), ultra-high stock density (UHSD) grazing and tall grass grazing systems. Most concentrate on beef cattle production. But can these systems translate to dairy cows? In a system where dairy profitability and milk production is dependent upon excellent forage quality and dry matter intake, can these type of grazing strategies make sense?
Mena Hautau, field and forage crop educator with Berks County Extension, recently decided to take a look at what type of “mob grazing” was already happening on southeast Pennsylvania grazing dairies. A Northeast Sustainable Agriculture Research and Education grant allowed her to observe grazing systems on four dairies which have already incorporated some type of intensive, managed grazing system, and are grazing tall grass, using frequent rotations, and grazing in higher densities. They were also all certified organic, although this was not intentional, and all were being managed by dairymen with more than two decades of experience. The dairies are grazing-based dairies with little grain or total mixed rations being fed.
Grazing term confusion
Hautau, speaking via a Penn State Extension webinar presentation, “Tall Grass Grazing for Dairies,” explained that there is much confusion regarding various grazing terms. The stocking density — the number of animals per acre per specified time period — is one defined characteristic of each system. MIG grazing has a stocking density of less than 50,000, while MOB grazing’s is between 50,000 and 250,000. UHSD grazing is mob-grazing with densities above 250,000, while tall grass grazing systems have stocking densities of 400,000-800,000, she said.
“I always thought that it could be very challenging for livestock producers,” when working with dairy animals, to achieve the forage quality and dry matter intake needed for milk production when implemeting “mob grazing” practices, Hautau said.
The study found that the Pennsylvania dairy farmers were using hybrid systems, incorporating some aspects of the various systems into a rotation that worked for their farms. Stocking densities were between 44,000 and 377,000 on the study farms. Grass was grazed tall, and animals were moved through paddocks — anywhere from .5 acre to 2.5 acres in size. The cows were rotated at least once a day to new pasture, with some farmers self-reporting three to five moves per day. Paddocks were rested between 30 and 49 days, on average, depending on the farm. Cows were out on pasture for roughly 20 hours per day on all of the farms.
“We found out on these farms that dairy cows are grazing taller, slightly more mature pastures, but they are leaving greater residues,” Hautau said. “These farmers were really using anything from a managed grazing system to a UHSD. Each farm that we worked with had their resource challenges and opportunities that impacted their ability to use this practice.”
Hautau and her team selected one paddock on each farm to study. Every time the animals were moved into that paddock, the team took pre-and post-rotation samples of pasture. They measured forage height, forage nutrition, took soil samples and measured pasture sward stratification. Twenty-five spaces were sampled for each paddock and averaged to determine forage height, via pasture stick. Then, 20 samples were hand-plucked per paddock to the height at which the cows were grazing, and mixed together, processed and frozen, then sent to Dairy One’s Ithaca lab for a ration balance and ESC (simple sugars) analysis.
The percentage of crude protein “was excellent” at over 20 percent CP, Hautau said. The Neutal Detergent Fiber decreased overall throughout the study, reflecting an increase in the quality of forage over time. Pasture quality was increasing with each rotation, she said. The Net Energy Lactation averaged between .6-.71 Mcal/kg, within the acceptable levels, but lower than numbers reported in other MIG studies.
“It’s a very acceptable forage for a dairy cow,” Hautau said. “These farmers are not grazing tall grass that’s stem-y, that’s over-mature. There’s still lots of quality there.”
During the study, Hautau visually observed that the cows were not putting their mouths on the soil. Instead, it seemed that they were preferring the canopy. Sward stratification measurements would determine whether or not the cows were showing preference based on forage height.
“We also want to understand how animals are selecting the pasture in the sward… how much the animals are consuming the different levels of that pasture,” she said.
Hautau’s study data showed that the cows were selectively consuming different levels of pasture, seemingly dependent upon the season, during the duration of the study. In the summer and fall of 2012, cows were consuming 70 percent of the forage at 13 inches tall or above, but only 20-30 percent of the forage between two and five inches in height. In spring 2013, they grazed this lower level of forage at 57 percent, while utilizing about 90 percent of the 13-16 inch forages. Forages over 16 inches tall were not as preferred as the slightly shorter sward. The middle swaths of forage were overlooked in the spring.
Soil fertility levels on all farms were all very good, with organic matter, ph, and potassium and phosphorous being measured. Each farm had a different soil type. The study did not measure compaction. Whether or not trampling compacts good clay soils, high in organic matter, needs to be further studied.
“It’s something we really have to be careful of in our climate,” Hautau said of compaction. “You really have to monitor your own farm for this.”
Another unanswered question is whether or not more dry matter was being produced, over time, on these managed grazing pastures. Whether or not grazing tall grass changes the pasture makeup, selecting for certain species over time, was not addressed in this study.
With expensive land in the region, many farms are carrying more animals per acre than is optimal for dry matter intake needs. During a 2012 drought, all of the farms altered their rotations and stocking densities to adjust to the diminished carrying capacity of the land.
“All farmers are very mindful about how they were going to cull, because they recognized, even with tall grazing, that they still needed more dry matter,” Hautau said.
She encouraged beginning farmers to focus on growing the best grass they can. Good quality forage is the key to managed grazing methods which work for dairy farms, and there is no one set rule for how to graze.
“Manage the grass first, as to what your goals are for nutrition, for animal health,” Hautau said, reminding participants that the dairy farmers studied were very experienced grazers.
“They utilized this experience and gradually moved into this system” she said. “And they are still refining it.”