Forage yield and nutritive value of cool-season and warm-season forages for grazing organic dairy cattle

Authors: RITZ, KATHRYN - University Of Minnesota; HEINS, BRAD - University Of Minnesota; MOON, ROGER - University Of Minnesota; SHEAFFER, CRAIG - University Of Minnesota; Weyers, Sharon

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2020
Publication Date: 12/14/2020
Citation: Ritz, K.E., Heins, B.J., Moon, R., Sheaffer, C., Weyers, S.L. 2020. Forage yield and nutritive value of cool-season and warm-season forages for grazing organic dairy cattle. Agronomy. 10(12). Article 1963. https://doi.org/10.3390/agronomy10121963.
DOI: https://doi.org/10.3390/agronomy10121963

Interpretive Summary: Organic cattle must graze pasture 120 days of the year and 30% of their DMI must come from pasture; however, grazing can be limited in drier summer months. Researchers at the University of Minnesota and the USDA ARS in Morris, MN, evaluated the forage quality and herbage mass of two grazing systems, a cool season perennial pasture or a combining cool seasons pastures with grazing on two warm season annuals, BMR sorghum-sudangrass and teff grass. The goal was to determine if alternative summer annuals can support grazing during the dry summer months. Warm season annual grasses had similar forage quality, but had higher herbage mass than cool season perennial pasture, indicating the potential benefits of incorporating these annuals into an organic cattle grazing system. Researchers, organic dairy producers will benefit from these findings. These results will help researchers, organic land and dairy managers and policy makers to develop, support and promote alternative grazing strategies to improve forage availability to maintain compliance with organic grazing regulations.

Technical Abstract: Two pasture systems with enhanced in-field and landscape level species diversity were analyzed for forage yield and nutritive value across the grazing season at the University of Minnesota West Central Outreach and Research Center organic dairy in Morris, MN, from 2013 to 2015. Pasture system 1 was a diverse-mixture of cool season grasses, legumes and herbs [perennial ryegrass (Lolium perenne), orchardgrass (Dactylis glomerata), meadow bromegrass (Bromus biebersteinii), meadow fescue (Festuca pratensis), alfalfa (Medicago sativa), white clover (Trifolium repens), red clover (Trifolium pretense), chicory (Cichorium intybus)]. Pasture system 2 was a combination of the same forages as pasture system 1 but included seperate monoculture pastures of warm-season grasses [brown midrib sorghum-sudangrass (sorghum × drummondii; BMRSS) and teff (Eragrostis tef.)]. Grazing of lactating cows was initiated when forages were 20 to 30 cm tall and paddock size for grazing was adjusted to leave 7 to 13 cm of refusals. Forage samples were analyzed with NIR spectrophotometry for dry matter, crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and total tract NDF digestibility (TTNDFD). Data were analyzed using the MIXED procedure of SAS, and independent variables for analyses were the fixed effects of system (1, cool season perennial pasture or 2, cool season perennial pasture and warm season annual grasses), month (June to October), forage (perennial cool season pasture, BMRSS or teff), year (2013, 2014, 2015) and their interactions, and date of harvest was a random variable. Across the grazing season, forage yield was greater (P < 0.05) in system 2 than system 1, due to greater (P < 0.05) forage yield during the summer months for BMRSS compared to cool season species and teff. Crude protein was greater (P < 0.05) for cool season perennial grasses compared to warm season annual grasses. The TTNDFD varied by month and year across the study for both treatment groups. In summary, yearly effects and climatic conditions may affect forage quality in both cool season perennial grasses and legumes and warm season annual grasses.