Plant growth and defoliation impact management of forage resources

Gillette – “By understanding how plants grow, producers can better manage grazing,” said Blaine Horn, UW Extension range and forage management educator for northeast Wyoming.

Horn and Mike Smith, rangeland management Extension educator, discussed ways to manage rangelands for sheep regarding defoliation, grazing management and distribution of livestock at the Northeast Wyoming Sheep Symposium held Sept. 4 in Gillette.

Managing defoliation 

“In Wyoming, we have cool season grasses that like to grow in temperatures between 60 and 70 degrees. This makes May an ideal time for growth because it has an average monthly temperature of 65 degrees with optimal precipitation,” Horn explained. “After May, temperatures go up and do not come back down until August or September, and rainfall does not return in required amounts until September.” 

Horn noted that animals need adequate forage for growth, making forage the actual crop that is just being marketed through a ruminant animal. 

“It is important for producers to appreciate how plants respond to grazing or browsing,” Horn stated. “Plants can be defoliated and survive, but they can only tolerate certain levels.” 

Biologic basis

“Plant morphology affects how plants respond to being consumed,” Horn explained. “As long as the plant has not reached genetic maturity, it will continue to grow.”

Growth of the plant is impacted by the location of the growing points. 

Grass tillers grow from basal buds, while leaves grow from the stem of a plant. If the growing point is defoliated by livestock, growth will cease. Horn noted that once the terminal bud is removed from shrubs and forbs, these plants will also stop growing. 

Defoliation also affects the roots of a plant, as plants need to produce both above- and below-ground biomass to survive. 

“Up to 50 percent of the leaves on a plant can be removed, and there will not be any impact on the roots,” Horn stated. “Seventy percent removal of above-ground plant mass results in 50 percent of the roots stopping growth for 17 days. Removal of 90 percent of the plant causes all roots to stop growth for 17 days.”

Grazing management

“Grazing management is important in maintaining the health and productivity of the range and the integrity of riparian zones and streams,” Smith stated. “This management is all about locating animals, moving them around and keeping them where they belong.” 

“Smaller animals, such as sheep, are more selective when they graze, while cattle and horses tend to prefer areas with the best or most grass forage available,” Smith explained. 

Smith noted that sheep will also travel uphill for water and will use a variety of habitats, preferring those with stemmed grasses and forbs. 

Sheep can also go for longer distances and periods of time without water than cattle. 

“Cattle prefer to stay near water sources,” he continued. “Cattle will travel up to two miles for resources but usually travel less than one mile. This distance shrinks in steep terrain.”

Proper distribution of livestock, whether utilizing one species or mixed, will decrease grazing pressure on specific areas.  

Nutritional resources

To distribute livestock, many producers use water, fencing or salt or molasses blocks, depending on the operation and location of the animals. 

“Water is always needed by the animals, and using water sources as a way to move them provides an opportunity to utilize a grazing system without fences,” Smith explained. 

However, hauling water and purchasing pipelines and other necessary supplies can be expensive. 

“Salt is attractive to animals but is not effective in many instances,” Smith continued. “Salt also has no effect on digestion of forages and little effect on forage utilization.”

Dry protein molasses blocks or lick tubs are more attractive to livestock and producers. 

The blocks showed up to 25 percent increase in forage use when the blocks were in a remote location. 

The supplements are most effective in winter or with dormant forage and are effective carriers for mineral mixes. 

Physical distribution

Fencing, another option for managing distribution, was described as effective but potentially expensive to install and upkeep. Smith suggested producers look into using low-cost electric or temporary fencing. 

Increasing the number of pastures used during the grazing season also improves the distribution. 

“The more pastures producers have tends to improve the distribution of livestock across those pastures, increasing harvest efficiency,” Smith stated. “Utilizing more pastures generally tends to be more effective from vegetation management standpoint.”

“Monitoring is also important,” Smith added. “Producers can only manage what they monitor. Effective management depends on monitoring trends and use as it occurs and looking for long-term changes in plant specie abundance or other pertinent ecosystem characteristics.”

Kelsey Tramp is the assistant editor of the Wyoming Livestock Roundup and can be reached at kelsey@wylr.net.