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Extension > Agriculture > Dairy Extension > Grazing systems > Forage quality of alternative grasses and its influence on milk production of grazing dairy cattle

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Forage quality of alternative grasses and its influence on milk production of grazing dairy cattle

Brad Heins and Kathryn Ruh

Organic dairy farmers in Minnesota are beginning to incorporate BMR sorghum sudangrass and teff grass in their grazing programs and are interested in learning more about these grasses. We conducted a study to determine how the forage quality of annual warm season grasses compares to perennial cool season pasture mixtures, as well as how they influence milk production and health parameters in grazing organic dairy cows.

We used 90 organic dairy cows to compare two different pasture systems at the University of Minnesota West Central Research and Outreach Center in Morris, MN. The first system (cool system, System 1) included a diverse mix of cool season perennial grasses and legumes such as perennial ryegrass, white clover, red clover, chicory, meadow bromegrass, orchardgrass, meadow fescue, and alfalfa. The second pasture system (warm system, System 2) was a combination of the cool season perennial mixtures and warm season annuals BMR sorghum sudangrass and teff grass. Perennial pastures were established in 2012. Warm season annuals BMR sorghum sudangrass and teff grass were planted in individual paddocks during the third week of May of each year. Forage samples were collected daily throughout the grazing seasons of 2013 to 2015. Dry matter was analyzed immediately after sample collection. Forage samples were tested at Rock River Labs in Watertown, WI for the forage quality characteristics neutral detergent fiber (NDF), total tract NDF digestibility (TTNDFD), crude protein (CP), and mineral content.

Forage quality was similar between cool season perennial pasture grasses and the warm season species evaluated in this study (Figure 1). Cool season pasture had higher average crude protein (23.0%) than the warm season grasses, but BMR sorghum sudangrass and teff grass still had adequate concentration of protein for lactating cow diets (18.5 and 17.5%, respectively). Dry matter was higher in cool season pasture (23%) and teff grass (24%) than BMR sorghum sudangrass (20%). TTNDFD was similar between all types of forage. The mineral composition varied between the different grasses.

Figure 1. Forage quality of cool-season and warm season grasses.

There were no differences in milk production, components or somatic cell score (SCS) between cows grazing only cool season pastures and cows in a system that incorporated warm season annuals. Average daily milk production was 32.3 pounds for the cool system and 32.5 pounds for the warm system. Milk production increased by 2 pounds per cow per day when cows were switched from grazing cool season pasture to BMR sorghum sudangrass (Table 1). There was also no difference in body condition score, body weight, or activity between systems. Cows in both systems followed similar trends in production including decreased production during times of high temperature and humidity. In 2015, cows in the warm system achieved higher production than cows in the cool system during July and August.

Table 1. Production of cows grazing cool season pasture and alternative forages
System 1 System 2
Cool Cool BMRSS Teff Oats/Turnips
Milk (kg/d) 32.3 abc 31.7a 34.0b 32.0ac 32.8abc
Fat (%) 3.9 3.8 3.8 3.8 3.8
Protein (%) 3.2 3.2 3.2 3.1 3.2
MUN 12.5a 13.3a 9.3b 10.5ab 12.5ab
SCS 4.1 4 4.1 4.5 3.7

Different superscripts denote significant differences across row (P<0.05)

During the first year of the study, cows in the cool season system needed to be supplemented with stored feed in a TMR due to a shortage of forage biomass in pasture, while cows in the system incorporating warm season grasses were still able to graze. The following year there were no differences between pasture systems. Therefore, warm season annuals in grazing systems for dairy cattle may be beneficial in certain years to compensate for weather that affects pasture production. Warm season grasses like BMR sorghum sudangrass and teff grass may be incorporated into a pasture system for grazing organic dairy cattle without sacrificing forage quality. Milk quality and production can also be maintained when warm season grasses are incorporated in a grazing system for organic dairy cattle.

August 27, 2016

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