Testing for high nitrates in forage recommended
Persistent drought conditions in Wyoming have increased the likelihood farm and ranch livestock could be affected by eating forages that accumulate nitrates during prolonged hot, dry periods.
Steve Paisley, beef Extension specialist at the University of Wyoming, suggests livestock producers should sample and test forages for nitrates during prolonged droughts.
"To properly sample forages, producers will need a hay probe to not only test the outside of the bales or stacks, but the inside as well," he said.
Hay probes are hollow cylinders with a sharp end, and, depending on the type of forage probe, the cylinder is pushed into the bale either by force or with a cordless drill. The probe then takes a core sample of the bale.
"A minimum of 10 bales from a susceptible field needs to be sampled to get an accurate test," said Paisley. "Nearly every county Extension office, local co-op or feed store should have a forage probe available for ranchers. The samples can be placed in a sealable bag and sent to commercial feed testinglabs such as Ward Laboratories or SDK Laboratories." Information about both is available online.
Paisley said samples can also be sent to the Wyoming Department of Agriculture's Analytical Services Lab at 1174 Snowy Range Road in Laramie; to contact the lab, call 307-742-2984.
Some plants are more likely to accumulate nitrate than others, according to Paisley. Crops capable of high levels of nitrate accumulation under adverse conditions include corn, small grains, Sudan grass and sorghum. Weeds capable of nitrate accumulation include pigweed, lambsquarter, sunflower and bindweed.
"Nitrate levels less than 3,000 parts per million are considered safe, but forages with levels between 3,000 ppm and 6,000 ppm require special feeding considerations to improve feeding safety," said Paisley. "Nitrate levels more than 9,000 ppm are considered potentially toxic and should not be fed as the only source of feed."
The UW Extension publication Water Quality for Wyoming Livestock and Wildlife has more information concerning acceptable and non-acceptable levels of nitrates in forages; go to www.uwyo.edu/ces and click on Publications on the left-hand side of the page. Click search bulletins and enter B-1183 in the Publication Number field. Once opened, scroll down to page 25, Chapter 6, Nitrate and Nitrite.
"Be aware of what plants are potential nitrate accumulators," said Paisley. "It is important to sample and test these feeds prior to use to determine potential feeding concerns. There are ways to mitigate the hazards of high nitrate feeds, such as blending with other feeds, feeding additional grain and by slowly adapting or adjusting the cattle to higher nitrate feeds."
Nitrates in forages do not in themselves cause poisoning, according to Paisley. Instead, they are converted to toxic nitrites within an animal's digestive tract.
"In cows and sheep, this conversion takes place by the bacteria in the rumen," said Paisley. "In horses, it is converted by the bacterial populations in the large intestine. The nitrites get into the blood stream and cause a change in hemoglobin, converting it to methemoglobin."
Paisley said the conversion to methemoglobin reduces the oxygen-carrying capacity of the blood. When a critical mass of hemoglobin has been converted, the blood can no longer supply tissues with oxygen, and the animals can suffer from a type of asphyxiation.
Plants accumulate more nitrates during drought years because proper plant growth is dependent upon adequate water, energy from sunlight and normal temperature ranges conducive for growth, according to Paisley. Plant roots absorb nitrates from the soil, and the nitrates are converted to amino acids and protein as the plant grows and develops.
"During drought years," he said, "the root system continues to absorb nutrients from the soil, but, because of the lack of moisture as well as abnormally high temperatures, plant growth is restricted, and the nitrates are not converted to protein and continue building up in the roots and the lower portion of the stalk."