Drought brings new worry for cattle, hay producers

Nitrate build up can endanger animals; testing suggested

Besides the on-going effects of the prolonged drought such as supplemental feeding, economic issues, and when things will turn around, there is another concern.

During times of prolonged drought, we begin to be concerned with nitrate accumulation in hay and pastures. Also, with the short moisture, many producers are looking at baling grain sorghums after they are harvested for grain. Both of these scenarios can cause unsafe nitrate accumulations.

Warm-season annual grasses, such as forage sorghums, sorghum-sudan hybrids (haygrazer types), grain sorghums, and the various millets can also accumulate nitrates to a level that is toxic to cattle during periods of dry weather.

Typical nitrate accumulation occurs with nitrogen fertilization followed by a period of drought, although toxic levels of nitrates have been observed in warm-season annual grasses with as little as 50 pounds of nitrogen per acre under drought conditions.

While aboveground plant grow th is reduced, nitrate uptake continues to occur and concentrates in the forage tissue.

Ruminants are af fected because microbes in the rumen are able to convert nitrate to nitrite. Nitrite is then absorbed into the bloodstream where it converts hemoglobin, which carries oxygen throughout the bloodstream, into methemoglobin, which does not carry oxygen. Cattle death is due to asphyxiation, or lack of oxygen to cells.

Get a test

The total level of nitrate in forage will determine whether or not the forage is safe to feed.

Remember: Nitrate levels in hay do not diminish with time.

Only a forage analysis for nitrate (currently $5 at the Texas A&M University Soil Testing Lab) will determine whether or not the fresh forage or hay is safe to feed to livestock.

The Milam County Extension office can assist you in obtaining the forms and procedure to sample for nitrates. Nitrate levels of 5,000 parts per million or greater may be dangerous to feed to animals and greater than 15,000 parts per million are toxic to most classes of livestock.

The official Texas A&M University advisory is to not feed forages that contain greater than 10,000 parts per million nitrate. The more conservative number of 5,000 ppm, however, may be a much safer number to use in actual practice.

Producers using warm-season annual forages or johnsongrass should have their hay crops tested prior to harvesting. Look at the forages carefully. If the forage to be harvested for hay has been under drought stress, there is a good likelihood that it is high in nitrates.

If a good precipitation event occurs and plant growth is reinitiated (good green color, no droopy leaves), then the forage may be safe to feed, but a forage analysis for nitrate would still be advisable.

Do not harvest the forage and then test! To do so could wind up costing you time, effort, and money and result in a hay crop that you will not be able to feed.

Likewise, cattle should not be pastured on warm-season annual grasses or johnsongrass if conditions are such that nitrate levels could be elevated to a toxic level. Again, only a forage analysis can determine if the forage is safe to graze.

Prussic acid

If nitrate toxicit y was not enough to worry about, there is also the issue of prussic acid (hydrogen cyanide) poisoning.

Forages belonging to the genus Sorghum can produce prussic acid following light frosts or drought. In well-cured hay crops, prussic acid is not a concern since volatilization of the compound into the atmosphere occurs during the field curing process.

Cattle, however, may succumb to prussic acid poisoning while grazing if plants have been subjected to drought stress.

Again, do not turn cattle into pastures of drought-stressed sorghums or johnsongrass. Wait until better growing conditions before pasturing cattle on any stressed warm-season annual plant or johnsongrass. Millets, while still capable of accumulating nitrates to a toxic level, do not produce prussic acid.

If you have any further questions, please call the Milam County Extension office at 254-697- 7045, email at milam-co@tamu. edu, or come by 100 E. 1st Street in Cameron.

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