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Posted 29 August 2006. Forage and Grazinglands. Producers Advised to Use Caution with Drought-Stressed Feed Texas A&M University. coals.tamu.edu Dallas, Texas (July 25, 2006) - Danger may be lurking as farmers try to market drought-stressed crops and livestock producers hunt for forage, said two Texas Cooperative Extension specialists.
Dr. Ellen Jordan, Extension dairy specialist in Dallas, said many growers are attempting to salvage drought-stressed corn and sorghum crops. One possible market is dairy rations. But some drought-stressed crops may harbor aflatoxins, prussic acid or high levels of nitrates, Jordan said. Aflatoxins are a poisonous by-product of the mold aspergillus, she said. Metabolites of aflatoxin are potent cancer-causing agents; thus government regulations specify milk must contain less than 0.5 parts per billion. To keep milk from becoming tainted, producers must adhere to U.S. Food and Drug Administration guidelines to keep aflatoxin in dairy feed at less than 20 parts per billion. Dr. Ted McCollum, Extension beef cattle specialist in Amarillo, worries some of the stressed crops also might be used to feed beef cattle. Aflatoxin in feeds can hurt the performance and health of beef cattle, McCollum said. For dry cows and yearlings, total feed should contain less than 300 parts per billion aflatoxin. For lactating cows and weaned calves, total feed should contain less than 100 parts per billion. "Thus, caution is required when considering the use of corn grown under stressful conditions," Jordan said. Extension plant pathologists recently collected samples from corn fields north of Dallas. These fields, being baled for hay with the stalks and ears included, tested positive for aflatoxin, she said. Several ears from two samples had measured aflatoxin rates of 590 parts per billion and 1,700 parts per billion, Jordan said. The pathologists analyzed kernels from the plants and found aflatoxin rates of 2,200 and 1,400 parts per billion. Because the kernels were one-third of the total plant weight, using this whole-plant hay for dairy or beef cattle would be difficult if not impossible, Jordan and McCollum said. Another problem in drought-stressed forages is high levels of nitrate, the specialists said. Excessive nitrate consumption can be fatal to cattle, McCollum said. Nitrate concentrations in excess of 1 percent in the dry matter are considered toxic. However, lower concentrations also can cause health and reproductive problems and impede growth. Nitrate concentrations less than 0.3 percent are regarded as safe for pregnant cattle and 0.3 percent to 0.5 percent are safe for other cattle, McCollum said. As levels surpass 0.5 percent, the risk of reproductive failure, health problems and reduced performance increases. Whenever nitrates are more than 0.44 percent of the forage on a dry-matter basis, feeding strategies are required, Jordan said. For example, when nitrates are between 0.44 percent and 0.66 percent of the dry matter in forages, the forage should be limited to half the dry matter in the ration of pregnant cattle. The third concern with drought-stressed crops is prussic acid, Jordan said, which accumulates in stressed sorghum, sudangrass, johnsongrass and sorghum-sudangrass hybrids. High levels of nitrogen fertilization can increase prussic acid accumulation, she said. Re-growth after a rain is often associated with prussic acid poisoning. As forage cures after cutting, however, prussic acid levels will dissipate, McCollum said, "So proper harvesting and baling practices can alleviate some potential problem." "Test forages to determine the level of prussic acid," Jordan advised. Levels of less than 500 parts per million on a dry matter basis are usually considered safe, while levels greater than 1,000 parts per million are considered hazardous and can be fatal to livestock, she said. Jordan said purchasing feed from reputable companies that properly monitor their crops is important, since statewide drought stress could boost the potential for aflatoxin, nitrates and prussic acid in most crops. "If you suspect your forages may be high in nitrates or prussic acid, consider ensiling the forage," Jordan said. "The ensiling process decreases prussic acid and nitrate concentration. The result may make the forage safe to feed, but retest to determine if dilution is still needed." Don't buy poor quality feed or feed ingredients, she said. "A good deal on feed can be very expensive if it contains aflatoxin, nitrates or prussic acid," Jordan said. For additional information on aflatoxin, prussic acid or nitrates, visit Extension's dairy Web site at: http://texasdairymatters.org/
Contacts: Kay Ledbetter Dr. Ellen Jordan Dr. Ted McCollum |
