As our livestock head out to pasture, we’re all thinking about how to time our grazing to get the most out of our pastures. To help with that, here’s an edited excerpt from “Pastures for profit: A Guide to rotational grazing.” This publication was written with graziers in the upper mid-west in mind (Minnesota, Wisconsin, Michigan, Iowa, Illinois, Indiana and Ohio). If that’s not you, the principles of rest, grazing at the best heights, and length of grazing periods still apply. You may just need to adapt to your own growing seasons, precipitation and forages.
Plant Yield and Quality
Forage growth is slow when plants are small and have few leaves (early spring growth or after grazing) and yield is low. As leaves get bigger, photosynthesis increases dramatically, allowing for rapid growth and increased yields. Prior to flowering, most pasture plants are growing as fast as possible if other factors are not limiting. As plants mature, growth slows since most energy is diverted to flower and seed production. While yield is highest at heading, quality is very low. Quality is high when plants are small and vegetative and declines as plants mature. This occurs because, as plants get larger and stemmier, a greater percentage of nutrients and dry matter is tied up in undigestible forms (such as lignin). Greater amounts of undigestible fiber result in lower quality forage with decreased amounts of total digestible nutrients (TDN).
The goal of a good grazing program should be to maximize both forage yield and quality. The best time to graze is immediately following the most rapid growth but before flowering and seeding, as shown below.
Species develop differently however and the best time to graze one grass species may not be the best for another. Table 7 shows the average heights at which to begin grazing grasses and legumes. At these heights, pasture quality is high, forage is easy to eat, and plants have recovered sufficiently from the previous grazing.
Rest Period Length
The rest period required is closely related to seasonal forage growth for different forages. Figure 6, below, shows what to expect.
• Legumes such as alfalfa, birdsfoot trefoil, and red clover need rest periods of about 3 to 4 weeks throughout the season.
• Cool-season grasses such as Kentucky bluegrass, ryegrass, orchardgrass, or timothy need as little as 2 weeks of rest during cool weather and 5 to 7 weeks during hot weather.
• Grass-legume mixes should be grazed when the grass reaches the ideal height.
• Warm-season grasses, such as sorghum/sudan or big bluestem, need to rest for 5 to 6 weeks during cool weather and about 3 weeks during hot weather
Plants under stress (drought, cold weather, poor soil fertility, etc.) will require longer rest periods. Optimal growing conditions, on the other hand, decrease the rest period needed.
Don’t Use the Calendar to Time Your Grazing
It is crucial, when deciding when to graze and how long to rest a pasture, that you move your animals according to the forage, not the calendar. If you graze too early, the pasture will be set back, desirable plants may die out, and weeds may take hold. If you graze too late, the grass becomes bunchy, loses palatability, and your production might suffer. There are times when you’ll want to purposely use shorter rest periods to weaken a pasture (say for interseeding legumes) or keep up with unusually fast growth. There are also times when you’ll need to use longer rest periods to let forage reseed itself, renew its root reserves, or be stockpiled.
Length of Grazing Periods
Controlling the amount of time a paddock is grazed is just as important as leaving adequate rest periods between grazing. If the grazing period is too long, newly grazed plants may grow back tall enough to be regrazed again within the same grazing period and can be damaged.
Use short grazing periods. Since livestock graze selectively, they will eat highest quality forage when first turned out onto a paddock and be forced to eat lower quality forage each day they remain in the same paddock. They also tend to eat more when first turned out onto a fresh paddock. Therefore, shorter grazing periods will provide for more uniform forage intake.
This is especially important for dairy farmers since change in forage quality shows up in milk yields. Many dairy farmers use one-day grazing periods; some move livestock after every milking. With other types of livestock, rapid moves are less beneficial and animals may be moved to new pasture every 2 to 6 days depending on the level of nutrition required.
Do not overgraze pastures. The closer you graze a pasture, the longer the rest period required for forage recovery. The higher the stubble, the more quickly the plant will be able to recover after grazing. A good rule of thumb is to leave 4 inches of stubble for cool-season grasses and legumes and 4 to 8 inches of stubble for warm-season grasses. Try to adjust the length of your grazing period to allow for these stubble heights. If you can’t leave these stubble heights, your forage will probably do all right if you give it adequate rest between grazing. A sure way to kill desirable species is to graze close and then graze the regrowth without allowing adequate rest.
If cattle are leaving excessive forage, you may wish to decrease your paddock size instead of lengthening the grazing period. You may have to lengthen the grazing period and/or increase the size of your paddocks mid-season to correspond to decreasing forage growth rates.
Seasonal Fluctuations in Pasture Growth Rate
There are a number of ways to provide high yielding, quality forage throughout the grazing season.
1. Reduce the number of paddocks grazed in the spring by using them to make hay. Put those paddocks back into the rotation in the middle of the summer and, if necessary, supplement your grazing animals with the hay made in the spring.
2. Plant portions of pasture to differ- ent species to stagger heading.
3. Plant legumes in cool-season grass pastures to provide more even summer growth (see Figure 6 above).
Pastures for Profit was written by Dan Undersander, Beth Albert, Dennis Cosgrove, Dennis Johnson and Paul Peterson. It has lots of great information about setting up a rotational grazing system. It covers animal needs, grazing patterns and their impact on pastures, figuring paddock sizes and set up, fencing, stocking rates and more. Download your free copy.