Authors of this piece are Aimee Hafla and Kathy Soder of the USDA-ARS Pasture Systems and Watershed Management Research Unit in Pennsylvania, and Mena Hautau, Cooperative Extension, Pennsylvania State University.
Ultra-high stocking density grazing, sometimes referred to loosely as “mob grazing”, is a grazing management practice generally characterized by high stocking density (units of live body weight/units of area; 500,000 + lbs/ac), small paddock size, mature forage, short grazing durations, and long forage recovery times (90 to 180 days). Those promoting this grazing strategy cite increased profitability through increased carrying capacity, improved animal performance, improved plant species diversity, and increased soil quality (improved organic matter, improved microbial action, and greater water holding capacity). Much of this anecdotal information has emerged from articles in farm press and trade publications and is specific to beef cattle in regions with climates much different than those in the northeastern U.S. We have received numerous inquiries from dairy farmers asking how to implement mob grazing on their farms, however there was no science-based information for this region from which we could make recommendations.
What is the Definition of Mob Grazing?
The term “mob grazing” can be quite ambiguous. A quick Google search of the term returns articles and blogs with descriptions of “high stock density”, “short duration grazing”, “high-intensity grazing”, “tall grazing”, and many more. Furthermore, during a field day, we handed out index cards to attendees (mostly farmers) and asked them to write down their own definitions of mob grazing. The responses we received were overwhelmingly variable, and included:
“Cattle grazing headed grass on the verge of rank; stocking density of greater than 100,000 lbs/acre.”
“More than 200 animals frequently moved on small acreages; grazing at a height that resembles high-quality dairy hay/haylage using very high stocking rates.”
“Grazing grass past ideal maturity so there is lower quality but higher quantity.”
“Grazing patterns to maximize pasture rotations and nutrition for well-balanced nutrition.”
Clearly the field day participants had very different ideas about the definition of mob grazing, however some common ideas did appear. To better understand how northeastern dairy graziers are implementing this practice, we looked at dairy farms in Pennsylvania and New York that described themselves as using mob grazing. Our purpose was to observe and describe the management practices and soil and forage quality.
The Case Study
Four organically certified dairy farms (3 in PA, 1 in NY) were surveyed at the beginning of the study to summarize their experiences and management practices. All farms had at least 15 years of grazing experience, and all had used some form of mob grazing for 2 to 8 years. Reasons for adopting mob grazing included savings of labor and machinery, continuing to provide a forage diet to cows, improved soil life and mineral availability, greater drought tolerance of pastures, perception of a “natural” system, and matching the productivity of the soil to a forage cropping system.
One representative pasture on each farm was identified as the “sample” pasture. We collected data from the sample pastures each time they were grazed from June to November of 2012 and from April to June of 2013. Data was collected during each farm visit, immediately prior to grazing. Due to the limited nature of this study we were not able to collect information from all pastures on all farms or to collect milk production data.
What Does Self-Described Mob Grazing on Dairy Farms Look Like?
The pastures we sampled ranged from 0.52 to 2.60 acres (Table 1), with an annual stocking rate that ranged from 1 to 4 acres per lactating cow. These pastures represented 1 allocation of fresh forage per move. Cows were offered fresh allocations between 1 and 5 times daily, depending on the farm. The farmers noted that the number of daily fresh pastures allocations was dependent on visual estimates of available forage before grazing, the number of cows grazing, and how many animals had been stocked on the pasture in previous years. Additionally, the number of fresh forage allocations offered per day were increased when forage quality was assumed to be low (based on visual assessment) in an effort to match animal requirements and available pasture nutrients.
Stocking density ranged from about 44,000 to 337,000 lbs/acre, which is generally lower than the 100,000 to more than 500,000 lbs/acre indicated by proponents of mob grazing with beef cattle. Forage height immediately before grazing was 11 inches, which is slightly taller than the 6 to 8 inches recommended for traditional rotational grazing systems. Days of forage rest between grazings ranged from 30 to 49 days, which is slightly longer than the 21-day cycle recommended for rotational grazing in this region, but much shorter than the rest cycle promoted by those using mob grazing in beef cattle systems, who often cite 90- to 180- day rest cycles. However, the farmers noted returning to pastures sooner than intended during the 2012 grazing season due to the unusually dry conditions. Cows consumed an average of 45% of the total available forage, with the majority of forage consumed from the upper layer of the canopy where there would be a greater proportion of vegetative leaves and some seed heads. While some seed heads were present, the pastures remained fairly vegetative and nutritious throughout the grazing seasons. Finally, soil mineral content and pH on all farms was within levels expected for this region. Soil organic matter values were also as expected for pastures in the northeastern U.S. (ranging from 3.2 to 4.1%), but did not exceed typical values, despite claims that mob grazing contributes to the rapid accumulation of soil organic matter within just a few years.
What Have We Learned?
The dairies observed in this study have take an approach to mob grazing that falls somewhere between the traditional rotational grazing systems used in this region and the current mob grazing definitions described by beef producers. The farmers in this study were grazing forages slightly more mature (taller) and implementing slightly longer periods of forage rest in their grazing systems, compared to rotational grazing. The goals of grazing dairy and beef operations differ, and there is a difference in how forgiving those systems are when nutrient intake mistakes are made. Dairy cattle require consistent, high-quality forage on a daily basis to optimize milk production. Inadequate forage quality or availability will be quickly reflected in bulk tank levels and the resulting milk check. Beef cattle systems may be more flexible from a daily nutrient intake standpoint, where the goal is average daily gain over a period of time. With mob grazing there is the possibility of overestimating nutrient intake of grazing dairy cows when more mature forages are grazed, and this could affect profitability. A high level of management is required to successfully transition to a mob grazing system. Grazing dairy farmers who are interested in adopting mob grazing should proceed by taking small steps and allowing the system (animals, forages, soils) to respond before making further grazing management modifications.
Finally, it is important to recognize that this case study only intended to describe a snapshot of management strategies used on dairy farms using self-described mob grazing. More comprehensive studies are needed to fully understand the transition and long-term effects of implementing this type of grazing strategy on dairy farms in the Northeast.