Dry and windy conditions of the winter of 2010 and spring of 2011 decimated the dryland wheat crop and severely impacted the quality and quantity of irrigated wheat due to heavy evaporation of irrigation water and stronger than normal late winter freezes. Hot weather throughout the spring and summer and the lack of help from Mother Nature has severely impacted the quantity and quality of the corn crop. Lack of moisture across the Southwest in general has led to lower than normal availability of forages.
The problem with ruminants is that even though we can use a fair amount of other agricultural by products, such as cottonseed or DDG from the ethanol industry, we still need to base the ration on at least one-third forage products (hays and silages), and for high producing dairy cows or lactating beef cows we need quality forages to make sure they receive adequate nutrients. And quality forages are a rare commodity. Currently, producers are buying hay from areas which have been blessed with an abundance of water this year, at premium prices and with a premium haul.
So what to do with the low quality drought-affected forages available locally?
Drought in and by itself does not necessarily reduce the quality of crops and despite the limited size plants can still contain concentrated levels of nutrients including high levels of fermentable sugars. Young corn prior to tasseling can contain 14 to16 percent CP.
Early cut forages commonly contain higher nitrate levels than the same forage when almost mature.
When plants are stressed by conditions such as drought, plant metabolism is interrupted and nitrates can accumulate in the leaves and stem of the plant.
Crops most at risk are annuals such as corn, oats, wheat, barley and sorghum. Legumes, such as alfalfa, are not typically known to accumulate significant levels of nitrate.
When livestock consumes feeds high in nitrates, these normal metabolic pathways are overwhelmed and very toxic nitrites accumulate in the bloodstream. Nitrites bind the hemoglobin and reduce the blood’s oxygen carrying capacity.
Adaptation: Rumen microbial populations can adapt to higher levels of nitrates over time, but rapid changes in dietary nitrate levels cause problems.
What are the symptoms of nitrate poisoning? Gasping, rapid respiration is the predominant sign, along with muscle tremors, rapid weak pulse, weakness, with the affected animals going down and into terminal convulsions.
What about nitrates in hay? Nitrates are soluble in water, which means that while the hay is in the windrow, rain will leach out nitrates along with important nutrients. However, hay dried quickly will lose very little nitrate.
How about ensiling? Ensiling will reduce the amount of nitrates to varying degrees and can be cut in half. Time in the pile helps to reduce nitrate levels.
How should high-nitrate forages be fed? Forages containing under 1,000 parts per million (ppm) nitrate-nitrogen (NO3-N) on a dry matter basis may be fed free choice or with no restriction on meal size. That’s provided the total level of NO3-N in the total ration, including water, is kept at a safe or low risk level. Stored forages containing higher levels generally require limiting meal size to avoid elevated methemoglobin levels in the blood and other toxic effects.
Animals should not be allowed to consume feed containing more than 0.8 percent nitrate (100 percent dry matter basis). Feeds containing more than this amount should be physically mixed with “nitrate-free” feeds to ensure the total nitrate level is below 0.8 percent percent. Samples may be submitted to feed testing laboratories for a nitrate analysis. These results must be viewed with caution, however, as there can be tremendous variation in nitrate content among plants taken from the same field. Feeding adequate levels of vitamin A and energy will help to reduce the potential for nitrate toxicity.
Robert Hagevoort, is a dairy specialist with the Agricultural Science Center at Clovis. He can be reached at 985-2292.