By Dr. David Brown, University of Missouri Extension
Forage remains the least expensive source of nutrients to maintain the sheep and goat herd. However, the drought condition experience across the state is affecting nutrient quality of forage in a variety of ways. During drought conditions, there is little or no grass growth, hence sheep and goats have access to older and less desirable pasture. In addition, drought stress reduces plant growth, ion uptake and nutrient metabolism.
The disruption of plant metabolism caused by water deficit leads to decreased concentration of nitrogen (N), phosphorus (P) and vitamin A in plant tissue. Consequently, drought stress plants contain low protein and increased nitrate levels.
Nitrate and nitrite poisoning have been reported in sheep and goats. Excessive levels of nitrates (>2500 NO3 ppm) are toxic to livestock. Since most producers are feeding hay to their animals, plants that are most susceptible to the accumulation of toxic levels of nitrates are Oat, Beet, Rape/ Turnip, Soybeans, Barley, Flax, Alfalfa, Pearl millet and Rye.
Some weeds such as Pigweed, Kochia, Jimsonweed, Johnson grass, Smartweed, Ragweed, Lambsquarter, Goldenrod, Nightshades, Bindweed, Canada thistle, Wild sunflower and Stinging nettle are also known to accumulate nitrates. General symptoms such as poor appetite, weak lambs or kids, abortions, poor growth, and general unthrifty conditions are frequently blamed on nitrate toxicity.
Brownish discoloration of the blood due to the presence of methemoglobin is another significant sign of nitrate poisoning. The key to avoiding nitrate poisoning is to have your forage hay tested and request the optional test for nitrate levels. For more information on forage analysis and nitrate toxicity, contact David Brown at 417-646-2419 ordavidbrown@ missouri.edu.
