|WILLIAMSON, JESSICA - Pennsylvania State University|
|Andreen, Danielle (elle)|
|SKINNER, HOWARD - Retired ARS Employee|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2020
Publication Date: 3/19/2020
Citation: Billman, E.D., Williamson, J.A., Soder, K.J., Andreen, D.M., Skinner, H.R. 2020. Mob and rotational grazing influence pasture biomass, nutritive value, and species composition. Agronomy Journal. 2866-2878. https://doi.org/10.1002/agj2.20215.
Interpretive Summary: Grazing management has come to be dominated by a handful of strategies over the last 50 years. Two of these, mob and rotational grazing, present stark contrasts in terms of methodology, along with the benefits and challenges for the plants, livestock, and producers reliant on them. We compared mob and rotational grazing systems over a 4-year period using a field grazing study at the Pennsylvania State University Hawbecker Research Farm. Our results indicated that mob grazing dry matter yields declined faster than rotational grazing, and that prolonged use of mob grazing eventually results in lower yields than rotational grazing. Additionally, pasture species composition was heavily influenced by grazing management style, with grasses persisting better under rotational grazing, and legumes persisting better under mob grazing. Finally, forage quality was impacted by management strategy, with rotationally grazed pastures having lower fiber levels than mob grazed pastures. While neither option is universally superior, producers may use this knowledge to decide which system is best suited for the production needs.
Technical Abstract: Forage yield and quality are principal concerns for ruminant livestock producers and can be greatly influenced by grazing management. Mob grazing, a strategy originally adapted for use in the western United States, has garnered attention in the Northeast, but impacts of greater stocking density and longer rest periods are unknown. Objectives were to compare the impacts of mob and rotational grazing on dry matter (DM) yield, forage quality, and botanical composition within and across four grazing seasons. Eight, 0.10-ha plots were established in 2014 as a randomized complete block with four replications, and seeded with alfalfa (Medicago sativa L.), white clover (Trifolium repens L.), orchardgrass (Dactylis glomerata L.), narrowleaf plantain (Plantago lanceolate L.), and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort]. Mob-grazed (MOB) plots were grazed twice year-1, (70 – 90 day interval), and rotationally-grazed (ROT) plots were grazed four to six times year-1, (when sward height reached 25 cm). Cumulative DM yield of ROT plots was greater in three out of four years, and exceeded MOB yield by 2,500 kg ha-1 at the final grazing. Within grazing season, ROT forage availability was more consistent, varying by only 1,400 kg ha-1 compared to 2,800 kg ha-1 for MOB. Grazing strategy altered botanical composition, with ROT favoring grasses and MOB favoring alfalfa. Forage ADF and lignin content were also consistently lower in ROT than MOB plots, indicating superior forage quality. These results suggest rotational grazing is likely more suitable for consistent, high-quality forage production in cool-season pastures common to the northeastern United States.