When discussing nitrate poisoning of cattle in Florida we tend to think of grazing winter annuals like ryegrass or small grains. However, nitrate poisoning can occur with cattle grazing perennial grasses like bermudagrass. One case of nitrate poisoning occurred when cattle were fed bermudagrass hay harvested from a poultry processing plant spray field. Another instance occurred when brood cows grazed bermudagrass pasture heavily fertilized with dairy cow manure. Nitrate uptake by plants is much faster in moist soil than in dry soil.
Nitrate concentration is highest in young plants and decreases as the plant matures.
Forages harvested or grazed at early stages of maturity will have high protein and TDN levels, and are very palatable to cattle. These forages also can have toxic levels of nitrate. Nitrate is lowest in the leaf because it is being synthesized into protein using energy produced by photosynthesis. Thus nitrate poisoning is more of a problem when cattle are forced to eat stems in either an over-grazed situation or when the forage is cut for hay. Suspect forages can be grazed or harvested for hay without problems once the forage reaches a certain stage of maturity.