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Forage quality of two different pasture systems incorporating warm and cool season forages for grazing organic dairy cattle
Two pasture systems (perennial and annual grass species) with enhanced in-field and landscape level species diversity were analyzed for forage quality characteristics across the grazing season at the West Central Outreach and Research Center organic dairy in Morris, MN for three years. System 1 was a diverse-mixture of cool season grasses and legumes (perennial ryegrass, white clover, red clover, chicory, orchardgrass, meadow bromegrass, alfalfa, meadow fescue). System 2 was a combination of perennial polycultures and annual-warm season grasses (BMR sorghum-sudangrass and teff grass). Grazing of lactating cows was initiated when forages were 20-30 cm tall and strip size was adjusted to leave 7-13 cm of refusals. Random samples of pasture forage were sampled every other day when a group of cows moved to a new paddock. Pasture clippings were randomly collected in a 0.76 m2 square of pasture. Forage samples were sent to Rock River Laboratory, Inc., Watertown, WI and were analyzed with NIR spectrophotometry for DM, CP, and total tract NDF digestibility (TTNDFD). Data were analyzed using the MIXED procedure of SAS. Independent variables for analyses were the fixed effects of system (perennial (1) or perennial-annual (2)), month (June to October), forage (perennial grass pasture, oats/turnips mix, BMR sorghum-sudangrass or teff grass), year (2013, 2014, 2015) and their interactions, and date of harvest was a random variable. The DM was 23.3% and 22.4% for systems 1 and 2, respectively (P=0.44). The CP was 23.0% and 18.0% for systems 1 and 2, respectively (P<0.001). The CP for system 1 was 20.9% in 2013, 23.2% in 2014, and 24.7% in 2015(P<0.05). The CP for system 2 was 14.6% in 2013, 18.9% in 2014 and 20.5% in 2015, and 2013 was lower (P<0.05) than 2014 and 2015. The TTNDFD was 54.6% and 54.9% for system 1 and system 2, respectively (P=0.84). The TTNDFD was 63.8% in 2013, 48.0% in 2014, 51.9% in 2015 for perennial grass pastures (P<0.01), and 59.3% in 2013, 46.3% in 2014, and 59.0% in 2015 for warm season annual grasses. In summary, CP was greater in perennial cool-season pasture systems; however, TTNDFD and DM did not differ between pasture systems. Yearly effects and weather may affect forage quality in both pasture production systems.
Keywords: grazing, teff, sorghum-sudangrass