Friday, July 06, 2012

TOP STORY >> Pastures could turn deadly in drought

Leader staff writer

The ongoing drought has the potential of turning pastures not only brown but also deadly.

The Cooperative Extension Service is warning farmers and ranchers against letting their animals graze since two cows have died from eating grass high in prussic acid, a cyanide compound found in several types of grasses when they are stressed by drought or frost.

The cattle deaths were in White and Van Buren counties.

White County extension agent Brian Haller said the best way to prevent prussic acid poisoning is to keep cows out of pastures that have the grasses known to contain the poison when they are over heated — grain sorghum, sorghum-sudan hybrids and pure Sudangrass.

Those grasses may be the only green in some pastures now and the cattle will be tempted to eat them. But the young, tender grass that will attract the cattle is highest in prussic acid and therefore the most deadly.

Haller said the grass is still useable, but only after it has been cut and baled. Baling crushes the stems and allows the prussic acid to evaporate, he said. But don’t turn the cattle back into the pasture after baling because the regrowth is deadly.

White County has about 50,000 beef cattle, Haller said. At least that was the number before the drought.

The first cutting of hay produced about half as much as normal, he said. Now many ranchers are selling their herds because they don’t have enough hay to feed them.

“We’re in a really serious situation,” he said.

“People need to get a plan and figure out what they’re going to do. We don’t know when we’ll get rain again. If you haven’t started looking for hay, you need to do that ASAP or find some sort of commodity feed (by-products of farm crops),” he said before Friday evening’s rain in part of the state.

Haller said some farmers and ranchers are low on hay not only because of low production this year but because they sold their extra hay last year to Texas ranchers who were trying to survive the drought there.

How do you know when cattle have been poisoned by prussic acid?

Symptoms such as anxiety, labored breathing and weakness appear minutes after ingestion and death usually follows within an hour. So there really is no cure, only prevention, he said.

The poison is also found in the wilted leaves of wild cherry trees, such as those found on a limb knocked down by wind or farm equipment.

Horses and pigs are less affected by the poison, but goats and sheep are at risk the same as cattle.

Tom Troxel, associate head of animal science for the University of Arkansas System’s Division of Agriculture, offered these suggestions in a recent news release for keeping cattle safe when feeding sorghums and johnsongrass during the drought and after frost:

 Do not allow animals to graze fields with succulent, young, short growth. Graze only after plants reach a height of more than 18 to 24 inches.

 Do not graze on drought-damaged plants in any form, regardless of height, within four days following a good rain. It is during this period of rapid growth that the accumulation of hydrocyanic acid in the young tissue and of nitrates in the stems is most likely to occur.

 Do not graze on wilted plants or plants with young regrowth. Do not rely on drought-damaged material as the only source of feed. Keep either dry forage or green chop from other crops available at all times. Uneven growth as a result of drought can best be utilized as silage or hay.

 Do not use frost-damaged sorghum as pasture or green chop during the first seven days after the first killing frost. Delay pasturing for at least seven days or until the frosted material is completely dried out and brown colored. Do not rely on frosted material as the only source of feed. Do not graze at night when frost is likely.

 Do not turn hungry cattle onto a pasture of sorghum, sorghum-sudan hybrid or johnsongrass. Fill them up on hay or other forage first and begin grazing in the late afternoon.

An option for using potentially toxic forage is to harvest it as hay or silage. Prussic acid levels decline in stored forages. Well-cured hay is safe to feed. If forage likely to have high prussic acid is ensiled, it is usually safe to feed three weeks after silo fill.

In addition to prussic acid, the drought has also increased the risk of nitrate poisoning from fertilizers in plants that have stopped growing because of lack of rain. Harmful levels have also been found in corn stalks that some farmers are using as feed because the pastures are dead, the extension service warns.

Another potential problem is the encroachment of poisonous weeds into hay fields. Fertilizer and herbicide usually keep the poisonous weeds out but Troxel said producers have cut back on those applications, allowing poisonous plants such as perilla mint and hemp dogbane to get a foothold.

“Plants such as perilla mint and hemp dogbane remain poisonous even in dry hay and can cause livestock poisoning when the hay is fed later in winter,” he said.

The drought also affects cropland where poisonous plants such as coffee senna, sesbania and sicklepod are found. Troxel warns that animals could be poisoned by eating hay made from drought damaged row crops if those crops are infested with the weeds.