Forage quality of alternative grasses and milk production of grazing dairy cattle

Brad Heins and Kathryn Ruh, U of MN Grad Student

The University of Minnesota, West Central Research and Outreach Center has been studying BMR sorghum sudangrass and teff grass, as organic dairy farmers in Minnesota are beginning to incorporate these grasses in their grazing programs and are interested in learning more about them.  We wanted to determine how the forage quality of annual warm season grasses compare to perennial cool season pasture mixtures, as well as how they influence milk production and health parameters in grazing organic dairy cows.

For our study, 90 organic dairy cows were used in a study to compare two different pasture systems at the 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 2013-2015. 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 levels 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

There were no differences in milk production, components or SCS between cows grazing only cool season pastures and cows in a system that incorporated warm season annuals.  Average milk production was 32.3 lb for the cool system and 32.5 lb for the warm system.   When cows switched from grazing cool season pasture to BMR sorghm sudangrass, production significantly increased by 2 lbs per cow per day (Table).  There was also no difference in body condition score, body weight, or activity between systems. Cows in both systems follow 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.

Production of cows grazing cool season pasture

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 difference 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.