Study looks at impact of warm season annual grasses for grazing organic dairy cows

May 13, 2016

Originally appeared in the MOSES Organic Broadcaster

By Kathryn Ruh and Brad Heins

It is important for organic dairy farmers to establish good pasture management to be able to follow the pasture rule for organic cattle. Organic cattle must graze pasture for at least 120 days of the year and 30 percent of their dry matter intake must come from pasture forage. Milk production is directly related to dry matter intake, which is directly related to the amount of available dry matter in pasture. For cows grazing pasture to be productive, there must also be healthy pastures that provide adequate forage quality and biomass to feed them.

Most pastures in the Upper Midwest consist of perennial cool season species. These grasses and legumes grow well in Midwestern soils and climate, and are considered high quality forage options that provide adequate nutrition for grazing dairy cows. However, during periods of high temperature and low precipitation, these perennial pasture species undergo a “summer slump” and have decreased growth rates. The decreased feed availability in pastures because of slower growth of these forages may lead to decreased milk production. In addition, farmers may have to feed stored forages, which can increase their feed costs.

Incorporating warm season annual grasses into pasture systems has been suggested as a solution, as these grasses will experience their fastest growth rates at the time that growth of cool season perennials slows. Some farmers may be hesitant to implement this solution as it is generally believed that warm season annuals have lower forage quality than cool season perennials.

Forage Study
The University of Minnesota chose to study 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 compares to cool season pasture mixtures, as well as how they influence milk production and health parameters in grazing organic dairy cows.

BMR sorghum sudangrass has been fed as silage to dairy cattle. Nutrition studies have been conducted in dairy cattle comparing sorghum sudangrass silage to corn silage, showing similar production. It is typically not grazed in a pasture system, so very little is known about sorghum sudangrass as pasture forage, and how it may affect grazing dairy cattle.

Teff grass originated in Ethiopia and is extremely drought and heat tolerant. It has occasionally been used by some rangeland cattle producers as emergency forage, but is usually fed as hay. Very little is known about the forage quality of teff grass, especially in a grazing system.

For our study, we compared 90 organic dairy cows in two different pasture systems at the West Central Research and Outreach Center in Morris, Minn. The first system (cool system) 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) 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 May 28 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, Wis. for neutral detergent fiber (NDF), total tract NDF digestibility (TTNDFD), crude protein (CP), and mineral content.

Cows were of Holstein and crossbred genetics and were blocked by breed, parity, days in milk, and randomly assigned to one of two systems. Cows were moved to a new paddock every two days, were supplemented 5 lb. of corn per day, and provided with free-choice mineral in pasture. Milk production data was collected daily. Percentage fat, percentage protein, MUN, and SCC were tested monthly. Body condition scores and weights of cows were taken biweekly. Cows were also fitted with SCR HR-LD tags to monitor daily rumination and activity across the grazing season.

Results

Forage quality was similar between cool season pasture grasses and the warm season species tested in this study. Cool season pasture had higher average crude protein than the warm season grasses, but BMR sorghum sudangrass and teff grass still had adequate levels of protein for lactating cow diets. Dry matter was higher in cool season pasture and teff grass than BMR sorghum sudangrass. TTNDFD was similar between all types of forage (P>0.05).

There were no differences in milk production, components or quality 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 difference in body condition score, body weight, or activity between systems. Cows on cool season grasses did have higher daily rumination than cows in the warm season system. 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.

Conclusion

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.

This study will be repeated for a third year to evaluate the economics of including warm season annuals in a pasture system compared to a system that uses only cool season perennials for organic dairy grazing operations. A continuation of this study is currently being conducted using a dual flow continuous culture fermenter, and results will include digestibility of the grasses used in this study, which was funded by the Ceres Trust.

Kathryn Ruh, a student at the University of Minnesota, took first place in the Organic Research Forum poster session at the 2016 MOSES Organic Farming Conference.

Brad Heins is an assistant professor of organic dairy management at the University of Minnesota’s West Central Research Center in Morris, Minn.

Article available in the MOSES Organic Broadcaster