Getting the most nutrition from a dynamic rotational grazing system involves understanding and maintaining healthy and productive grasses.
Why it matters: Rotational grazing can be an economical use of land and forages for some livestock farmers.
Above ground, forage species are ready to be grazed when they reach three or four leaves, but below ground the roots also need to be at the ideal stage.
“Roots are really important because our perennial forage species store extra energy reserves in their roots, and the lower part of the stems,” says Christine O’Reilly, forage and grazier specialist with OMAFRA. She was one of the speakers during the Ecological Farmers of Ontario Sheep Grazing Management Webinar held virtually in March.
The plant relies on the energy from the lower stems and roots to regrow as it has been removed from a photosynthetic state when the upper leaves have been eaten off by livestock.
“The new growth is going to start within five days after the plant has been grazed. The plant will start to draw on those energy reserves, and the root system begins to shrink as the plant is drawing carbohydrates out of the roots and lower stem.”
Tillers will begin to grow at this stage, within two weeks, or longer, pending rainfall.
“It’s very tempting at [tillering] to put your livestock back. But, it would be very stressful on the plant to turn out livestock at this particular stage because they don’t have that backup energy source.”
Farmers should wait for the plant to have three or four fully developed leaves as the plant has a chance to produce more sugar than required to fuel the regrowth.
O’Reilly says to delay reintroducing livestock to the pasture so that the roots have time to recover.
“There is some green regrowth happening on top, one or two leaves. But those roots haven’t had a chance to grow back. If we’re hitting around this point, that’s overgrazing,” says O’Reilly.
“It’s less about how closely you graze and more about where in that grazing and recovery cycle that grass plant is. It’s all about timing.”
Overgrazing a pasture happens if animals are turned out too early, if they are left in the same pasture for too long, or if they are brought back in too soon and the plants haven’t had enough time to recover.
“How early is too early in the spring? Grasses go through similar growth in the spring as they do after they have been grazed.”
In the spring, leaves from the previous year are dead and are not photosynthesizing, requiring the plants to draw from their energy reserves to fuel the spring growth.
“We would want to wait until grasses have three to four new leaves before being grazed [in the spring].”
As well, pastures can be overgrazed by livestock being left in the paddock for too long.
“As a general guideline, there is the five-day rule. All livestock should be removed from a paddock within five days or less to prevent overgrazing. It comes down to the amount of time it takes for these grass plants to mobilize their energy reserves.”
If the livestock is left on that grass for more than five days the grass has likely begun to retrieve nutrients from their energy reserves for new growth.
“That new leaf material is the sweetest, most palatable delicious leaf material in the whole pasture. When [the livestock] take a second bite, that is super stressful on the plant. Ideally, we can get them out of there before that new regrowth starts to happen.”
“It doesn’t matter what kind of animals, or what kind of forage [is being grazed], that rest period is absolutely critical,” says Jim Johnston with Pasture Hill Farm where they pasture both cattle and sheep.
Finally, overgrazing can occur when livestock is introduced back into the pasture too soon following removal.
When removing livestock from the pastures it’s important producers leave a bit of leaf material behind so they can act as “solar panels” for photosynthesis, and speed up the recovery.
As well, rainfall and nitrogen, the most limiting major nutrient that grasses require, will play a factor.
Johnston says forage species also play a role in regrowth timing.
Orchardgrass, a common pasture grass used in Ontario, has very rapid regrowth.
Johnston says in his area of Northern Ontario, in the last week of May to the beginning of June, he can graze orchardgrass, and one day later he can measure a centimetre of new growth.
“It just comes back so quick, whereas you do the same thing with timothy or brome grass and you’ll find regrowth much slower,” says Johnston.
Johnston says that during the springtime while using older mixes for pastures, beef cattle and sheep can be returned to their pastures within three to four weeks, or 25 to 30 days. The rest periods during late summer and fall tend to be longer at 40 to 50 days.
“There are a couple of other reasons you might want to have longer rest periods. Certain legumes, especially birdsfoot trefoil, will self-seed. If you have the option… it will go back in the soil, then you’ve kind of re-seeded your pasture that way,” says Johnston.