The backbone of Southern pastures — bermudagrass and bahiagrass — are awakening from their winter slumber. That means they are starting to use stored carbohydrates to initiate regrowth.

Mark Mauldin, an extension agent with the University of Florida, cautions livestock producers not to be too quick to get cattle onto these warm-season perennial pastures.

“When spring arrives, and the grasses begin to break dormancy, their supply of stored energy is low because it has been slowly consumed all winter long,” Mauldin explains. “Then they expend considerable energy growing new leaf tissue. At this point, the plants have very little energy reserves left.”

Photosynthesis in the green leaf tissue is what rebuilds a plant’s energy supplies. These accumulating carbohydrates are used for leaf and root growth, but some are destined to replenish the plant’s stored energy inventory. This refueling of stored carbohydrates is what will later be consumed for regrowth after the plants have been grazed or harvested.

“Drought stress, cool nighttime temperatures, relatively short days, and early, limited leaf area make early regrowth and replenishment of stored energy a slow process,” Mauldin explains. “Insert hungry cows too early and the process grinds nearly to a stop. Plants become more susceptible to disease, insect, and especially drought stress. Conditions that would otherwise not be an issue can quickly become serious problems. Even if outside stressors and their potentially catastrophic impacts are avoided, there is still a price to pay for grazing too early,” he adds.

Mauldin says that plants — if grazed too early — will shift resource allocation away from root growth in favor of leaf tissue production. Moreover, the plants had naturally sloughed off lots of roots over the winter, and the tissue needs to be replaced for the effective capture of water and nutrients. A plant’s inability to rebuild its root system will negatively impact performance and make the plant much more susceptible to drought.

“The longer that plants lack adequate leaf area, the weaker they become until they eventually die,” Mauldin asserts. “At field scale, this presents as a thinning stand, which leads to an increase in weed pressure and a considerable decline in overall productivity.”

The effects of overgrazing pastures as they are transitioning to warm-season perennials are magnified because grasses are more fragile than they are later in the year.

“The same grazing practices that are perfectly fine and sustainable in the summer can cause long-term problems if done in the early spring,” Mauldin says. “Let the grass get further ahead of the cows than you normally would before the first grazing in the spring. Be sure to graze off no more than half of the standing biomass the first time you graze the pasture. Just an extra week or two of growth prior to the first grazing can go a long way toward maintaining a strong, healthy pasture that will ultimately result in more season-long forage production,” he adds.

Further complications

If perennial warm-season pastures were overseeded with cool-season annuals such as ryegrass, the spring transition period becomes even more challenging. The annuals must be grazed sufficiently to prevent them from shading out the perennial as it breaks dormancy. Mauldin explains that shade has the same negative effect as grazing too early, but it can be even more damaging because photosynthesis is severely hindered under a dense canopy of annual forage.

“Shading can be prevented through frequent, light grazing, which tops the annuals and allows light into the canopy,” the extension agent suggests. “Be careful not to graze the annuals down below the height of the perennial grass. This takes quite a bit of active management and a willingness to move cattle — sometimes quite frequently.”

If drought conditions develop and the grass stops growing, Mauldin cautions to not let the cows graze it down to the ground, as might be done in the fall. Rather, he recommends pulling them off pastures when there are still several inches of leaf growth and revert to feeding hay.