Livestock producers struggle during times of drought to provide adequate grazing and forage resources to meet the nutritional needs of their animals. However, having adequate volumes of forage available may not be the entire answer to this challenge, says Jim Krantz, SDSU Extension Cow/Calf Field Specialist.
"When plants are stressed such as during times of drought, nitrates can accumulate to toxic levels," Krantz said of the naturally occurring substance in plants. "This accumulation occurs primarily in the lower portions of the plant such as the stalk or stem and less in the upper portions such as the leaves."
Krantz explains that when animals eat forages with toxic levels of nitrate, the excess nitrate prevents animals from converting the forage to amino acids and protein resulting in the formation of nitrites.
"The excess nitrites are absorbed directly into the blood stream where they combine with hemoglobin to form methhemoglobin. Hemoglobin can transport oxygen while methhemoglobin cannot and asphyxiation can occur," Krantz said.
If producers suspect high levels of nitrate in their forages testing can be done to establish the levels of nitrates present, or not present, in the plant.
How to test forage for nitrate
"Proper sampling will dictate the accuracy of the results from testing," Krantz said. "In addition, grazing method will reveal direction in the sampling process."
In areas where livestock are allowed limited access to forage, Krantz says testing the upper portions of the plant is recommended, as they will not be left there long enough to consume the lower portions of the plant.
In rotational grazing systems, or those where livestock will be confined for the entire season, he says sampling should focus on the lower third of the forage, where higher concentrations would be expected.
"Samples need to be representative of the entire grazing resource. They should be a composite of about 10 to 15 areas with similar fertility and moisture," he said.
Krantz adds that mixing plants from "good/bad" portions of a field is not recommended as each area should be tested individually. When collected, samples should be placed in a paper bag so that there is no mold build-up.
He recommends that moist plants, such as silage or wet plants should be placed in plastic bags and put in a cooler with ice packs. They should be delivered directly to a lab the same day or shipped overnight with ice packs.
"Storage of moist samples in plastic bags at room temperature will encourage mold growth, and reduce nitrate levels, resulting in inaccurate results," Krantz said.
Visit www.foragetesting.com for a list of labs where samples can be sent for nitrate testing.
For more information on nitrate levels in forages or other livestock related resources, visit iGrow.org.