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An antidote to the summer slump

C.C. Nieman, D.S. Schaefer and K.A. Albrecht for Progressive Forage Published on 27 February 2020
Dairy steers graze Sudangrass

Midwestern pastures are generally dominated by cool-season perennial forages that are productive in spring but have slow growth in mid- to late summer.

This growth pattern causes challenges for livestock producers attempting to match the intake requirements of grazing livestock to the forage growth pattern. However, there are several options to help manage the uneven forage distribution.

One strategy is to incorporate warm-season annual grasses into rotational grazing systems. Warm-season annual species are planted in late spring and experience the greatest growth during the warmer, drier conditions of midsummer, thereby providing forage when growth of cool-season grasses begins to slow.

There are several different warm-season annual grasses suitable for pastures in the Upper Midwest. Sorghum-sudangrass, sudangrass and corn are just a few options. Sudangrass and sorghum-sudangrass are the same species but differ in their anatomical structure and growth characteristics. Sudangrass is more suitable for grazing because it is thin stemmed and regrows quickly, while sorghum-sudangrass has thicker stems and higher yield, suitable for either grazing or silage.

Dairy steers graze sudangrass

Both sudangrass and sorghum-sudangrass contain prussic acid. Therefore, care should be taken to ensure that sudangrass or sorghum-sudangrass plants are at least 18 inches tall before grazing. Additionally, they should not be grazed immediately after a freeze or drought, as those events greatly increase the risk for prussic acid poisoning. Corn is another warm-season grass option for the Upper Midwest, of which high yields are the major benefit.

Warm-season annuals on the farm

Olaf Haugen utilizes warm-season annuals to supplement his cool-season grass pastures during the “summer slump” on his dairy farm, Springside Farm in Canton, Minnesota. Haugen uses brown midrib (BMR) sorghum-sudangrass or BMR grazing corn, generally planted after winter rye on 10% to 15% of his total grazing acres. Often, these are acres due for renovation, and cool-season perennial species will be planted after grazing off the warm-season annual in late summer.

Haugen aims to graze the warm-season annuals approximately 60 days after planting and will graze for 30 to 40 half-days. His cattle are rotationally grazed and spend 12 hours on the warm-season annuals and 12 hours on cool-season perennial pasture. Haugen says he generally sees an increase in milk production when using the warm-season annuals, particularly corn. He attributes this to the greater available dry matter for grazing, because during midsummer there is insufficient dry matter available from his cool-season pastures.

Recent warm-season annual research

Despite the potential for increased forage production of warm-season annual grasses during midsummer heat in the Upper Midwest, there is little information regarding animal production when grazing these species. A recent three-year research project conducted at the University of Wisconsin Arlington Agricultural Research Station aimed to investigate two warm-season annual species for summer grazing. For this experiment, researchers had two treatments, BMR sudangrass interseeded into kura clover and corn interseeded into kura clover.

Kura clover was used in this study to provide ground cover because in the Upper Midwest many pastures are relegated to landscapes prone to erosion, and kura clover can reduce soil loss and nutrient runoff. In early June of each year, BMR sudangrass (ProMax) was drilled at 25 pounds per acre and a conventional corn variety was drilled at 30,000 seeds per acre into chemically suppressed kura clover.

For this experiment, stocker cattle were allowed to strip graze the corn-kura clover mix once for 24 days in mid-July to mid-August. This constraint is because the growing point for corn is consumed when cattle graze and corn cannot grow back. However, sudangrass can be re-grazed, and thus, BMR sudangrass-kura clover mixtures were grazed for two 24-day sessions spanning mid-July to mid-September, for a total of 48 days.

Research results

Favorable weather conditions and rainfall allowed for excellent forage growth for all three years of the study (2014-16). Forage quality of both mixtures was adequate for growing steers, maintaining crude protein levels between 12% and 18%. Heat and humidity in 2016 caused heat stress in grazing cattle and severely reduced average daily gain (ADG), though ADG in years one and two were excellent, averaging 1.9 pounds per day and did not differ between corn-kura clover and sudangrass-kura clover. Gain per acre averaged 245 pounds per acre on corn-kura clover, which was only grazed for 24 days, and averaged 316 pounds per acre on sudangrass-kura clover grazed for 48 days. Gain per acre was greater on sudangrass-kura clover due to the extra grazing days.

Challenges and practical management tips

Although warm-season annuals have demonstrated promise, producers still need to weigh several management considerations. Haugen emphasizes that for warm-season annuals “establishment can be challenging” and producers need to apply additional and specific management for these species. Haugen suggests the use of a no-till drill and herbicide for weed suppression, or tillage.

Considering sorghum-sudangrass establishment, soil temperature is also important. Haugen says, “I’ve seen people try to use these early in the year before temperatures warm up or late in the fall,” but sorghum-sudangrass requires soil temperatures of at least 60 to 65˚F, generally around early June. Haugen also says that on his farm in southeastern Minnesota, he expects sorghum-sudangrass growth to slow by the end of August, resulting in a narrow 90-day window for growth.

When considering grazing corn, Haugen suggests a planting population of 100,000 to 140,000 seeds per acre, much greater than the 30,000 seeds per acre recommended for grain production. The higher seeding rate will result in smaller stalk diameters and greater leaf dry matter. Even at the higher seeding rate, Haugen estimates seed corn cost around $0.50 per pound, or about $30 per acre.

Choosing a warm-season annual

When comparing sorghum-sudangrass to corn for filling the summer slump, Haugen finds that in years with adequate moisture, corn will produce more biomass than sorghum-sudangrass. He estimates corn produces 3 to 4 tons of dry matter per acre in 60 days; while sorghum-sudangrass may yield similarly, it will take 75 days and two grazings. Alternatively, the research project found the extra grazing days on sudangrass resulted in greater animal gain per acre and may even extend grazing into early fall.

However, for Haugen’s purposes, sorghum-sudangrass grazing may extend beyond the optimal time for cool-season perennial planting in mid-August. Therefore, before incorporating warm-season annuals, producers need to consider how these species fit into their current pasture forage production system.

Though warm-season annuals require some additional management and foresight, both research and practice show these species can fill the summer slump in productivity, while choice of species enables flexibility in designing Upper Midwest grazing systems.  end mark

PHOTO 1: Dairy steers graze sudangrass at the University of Wisconsin – Madison Arlington Agriculture Research Station. Photo by Vance Haugen.

PHOTO 2: Dairy cows graze corn at Springside Farm in Canton, Minnesota. Photo by Christine Nieman.

D.S. Schaefer is in the department of animal science at the University of Wisconsin.

K.A. Albrecht is in the agronomy department at the University of Wisconsin.

C.C. Nieman is in the animal science department at the University of Arkansas. Email C.C. Nieman.

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