The hot dry weather that typically accompanies the months of July and August reduces the growth and production of cool season pasture grasses.
It can be a challenging time to balance forage supplies, pasture health and livestock numbers.
One option that some graziers use to fill in this summer slump period is warm season forages. At temperatures above 80 degrees Fahrenheit, and until about 95 degrees Fahrenheit, warm season forages thrive and can grow rapidly.
Common annuals
Warm season forage options include both annuals and perennials. Some common annuals are sudangrass, forage sorghum, sorghum x sudangrass hybrids, pearl millet, annual lespedeza and corn.
Warm season perennials include the warm season grasses such as switchgrass, big bluestem and Eastern gamagrass, legumes like alfalfa and sericea lespedeza and forbs such as forage chicory, a short-lived perennial.
Best utilization
In general, the best utilization of warm season forages is obtained through the use of strip grazing. Just like the management of cool season pastures, confining livestock to paddocks that provide one to three days of grazing will result in more even grazing and more uniform manure distribution.
The use of warm season annual grasses in the grazing rotation can provide two to five tons of forage dry matter with multiple grazing passes in July and August and into September.
Summer annual forages in the sorghum family which includes sudangrass, forage sorghum and sorghum x sudangrass hybrids, all have the potential for prussic acid poisoning.
Prussic acid
Prussic acid is also known as hydrogen cyanide. Prussic acid levels can increase in these plants under any condition that stresses plant growth, such as drought or frost.
Conditions that cause plant injury such as cutting, trampling and bruising can also increase prussic acid levels in the plant.
According to the Ohio Agronomy Guide, the risk of prussic acid poisoning can be reduced by grazing at the proper height and by avoiding grazing during periods of plant stress such as before a frost, after a frost or during and shortly after a drought.
The Ohio Agronomy Guide recommends grazing sudangrass and pearl millet at 18-24 inches in height and leaving a 6- to 8-inch residue.
Sorghum x sudangrass hybrids and forage sorghums should be grazed at the 30- to 36-inch height and again leave a 6- to 8-inch stubble. When a 6- to 8-inch stubble is left, it may be possible to do a grazing pass every 14 to 21 days.
Experience
Based on experience here in Athens County with sudangrass and sorghum x sudangrass varieties, leaving a shorter residue definitely slows down the regrowth response and lengthens the time between grazing passes.
Experience and forage testing has also shown that quality, both crude protein and energy content, drops off rapidly once these forages get to boot stage and beyond. Graze them at a vegetative stage. All of the warm season annual forages respond well to nitrogen.
The guide recommends 60 to 70 total pounds of nitrogen for a 3- to 4-ton/acre yield goal and around 100 pounds of nitrogen for a 5- to 6-ton/acre yield goal when a warm season annual forage is planted into a former grass sod.
Most efficient use
The most efficient use of nitrogen is obtained by dividing the total nitrogen amount into split applications after each grazing pass. The use of nitrogen does bring up another potential animal health concern and that is nitrate poisoning.
All of the forages in the sorghum family plus millet and corn can accumulate high nitrate levels in a drought condition. The same grazing precautions recommended to reduce the risk of prussic acid poisoning can reduce the risk of nitrate poisoning.
Avoiding excessive nitrogen fertilization can also reduce the risk of nitrate poisoning. The use of lespedeza, both the annual varieties and the perennial sericea lespedeza is better adapted to the southern third of Ohio.
They generally are lower yielding than other warm season forages, particularly other warm season annuals, but they can be grown on low pH and low phosphorus soils.
In addition, lespedeza contains tannins, which are usually associated with decreased livestock intake, but there is some research that has shown tannins may have some anti-parasitic properties.
Goats
Goats seem to eat lespedeza readily and combined with the possible anti-parasitic properties of the tannins, it has become a warm season forage that a number of goat owners are utilizing.
Warm season perennial grasses will produce 65 to 75 percent of their total tonnage from mid-June to mid-August. Don’t begin grazing until these grasses reach 16 to 20 inches or more in height.
They must be managed so that each grazing pass leaves a 5- to 6-inch stubble for best regrowth and plant vigor.
Forage chicory is a perennial that generally will persist about three years, but with careful management may exceed this time frame. Chicory is a leafy plant that is high in crude protein and digestibility.
Although it begins growth with the cool season grasses, it has a deep taproot that gives it drought tolerance and it produces well even under hot, dry conditions.
Yields of three to four tons of dry matter are common. After the seeding year, chicory has a tendency to bolt and produce a stem, which reduces plant palatability and leafiness.
Minimize bolting
Grazing should be timed to minimize bolting. A 1.5- to 2-inch stubble should be left after grazing. Chicory will respond well to nitrogen. Apply 50 to 75 pounds of total nitrogen per growing season in split applications between grazing passes.
Some sheep and goat producers are utilizing chicory because it contains sesqueterpine lactones, plant compounds that some research studies have linked with anti-parasitic properties.
Alfalfa is a perennial legume that produces well during the summer period. Under proper soil pH and fertility conditions yields of 4-7 tons/acre should be achieved.
Use strip grazing and a stocking density that results in forage removal within five to seven days. If the grazing period is longer, there may be regrowth from the crown and new shoots will be damaged.
Alfalfa should be grazed close enough to insure that regrowth comes from the crown and not from stems.
A more intensive management system of moving livestock every one to three days may work best. Under good management, a grazing pass might be made every 25 to 30 days.
Alfalfa can provide a high crude protein and high energy feed. It is probably best utilized in a grazing situation with young growing animals or with dairy cows.
Bloat
Bloat is a concern when alfalfa is grazed, particularly if livestock have been grazing pastures with a low legume percentage.
In order to reduce the risk of bloat some guidelines can be followed. Do not turn hungry livestock in to an alfalfa paddock or in to an alfalfa paddock heavy with dew.
Let livestock graze on another pasture or eat hay during the morning, then once the dew is off, move them into the alfalfa.
Provide an adjustment period of five days in this manner to let the rumen get accustomed to alfalfa before grazing alfalfa full-time.
Although the production of cool season pastures decreases during July and August, the use of warm season forages can help the grazier fill in this production slump and maintain good livestock gains and body condition.
More information
For more information about the use of warm season forages contact a member of the OSU Extension Forage Team.
