Statewide
In my September 26, 2012 Sorghum Tip I highlighted nitrate and prussic acid in the sorghums used for forage. Texas A&M AgriLife’s main document, “Nitrate and Prussic Acid in Forages,” (E-543) can be viewed/printed/downloaded here.
There is one key difference in these compounds in forages: prussic acid dissipates in properly cured hay whereas nitrate remains fixed. Both are a danger to grazing cattle. I commonly see problems in the understanding of prussic acid (which is mostly in the leaves, the first portion of standing forage cattle would consume), how to test it, and what test results mean. Prussic acid sample collection is tricky in that how the samples are handled can skew the results. In 16 years on the job in the Texas High Plains, I feel the most reliable results—and the best interpretation of what these results mean—is found by using the services of Texas A&M’s Texas Veterinary Medical Diagnostic Lab, which has full-service labs in College Station and Amarillo. Laboratory staff are particularly keen on proper sample collection and they welcome your phone call to ensure you do this properly.
What do prussic acid test results mean?
As noted above, prussic acid is tricky to test for. Years ago testing labs most likely had a set concentration (in ppm) above which it was recommended you not feed the forage in its current condition. Two references I know of suggest differing ‘safe’ levels, one at 250 ppm, and another at 170 ppm. TVMDL recognizes; however, that this concentration is subject to numerous variables, and TVMDL generally advices that if the sample detects prussic acid that the forage be handled with caution.
Crazy results on prussic acid testing!
Recently a Dawson Co. producer called to say that an area cattleman he sold baled sorghum stalks to had an animal die and a local veterinarian thought it was prussic acid. The grower collected a sample of the hay and had it analyzed at a private testing lab that reported about 180 ppm prussic acid. Yes, that would normally be a potential concern; however, only then I was told the sorghum hay was from the 2013 harvest, which the grower mowed and baled in November, possibly even early December! Now a lab is telling us these many months later that there is prussic acid? No way, not in sorghum stalks that sat out there a month or more after harvest, were dried down before baling, and sat for another 9-10 months in a bale! (Even though the veterinarian said he thought it was prussic acid?) I referred the grower to TVMDL for another test, and as expected there was no detection of prussic acid.
