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Scientists Say Ranchers Need Better Locoweed Field Test

LAS CRUCES - New Mexico State University scientists are searching for a field test to identify cows that seem to seek out locoweed, a finding that could help ranchers keep their animals free of the neurological disorders caused by the toxic plant that dots the state's sprawling northern plains.

Andres Cibils, a New Mexico State University livestock grazing expert, examines a clump of locoweed. Cibils is seeking a procedure to keep New Mexico cattle ranches free of neurological damage caused by the weed, a tough task since some cattle appear naturally drawn to the toxic plant. (04/11/2005) (NMSU Agricultural Communications Photo by J. Victor Espinoza)

"Our goal is to develop a quick, inexpensive protocol that ranchers can follow in the field to keep their herds loco free," said Andres Cibils, a livestock grazing expert with NMSU's animal and range sciences department. Today, a rancher's keen eye is about the only tool available to cull these weed-munching animals.

Normally, less than 10 percent of cattle in a shipment will naturally chow down on locoweed, Cibils said. Most of the cattle have never seen the plant before. But something about this dangerous plant entices a few to the dark side, he said.

A toxic member of the pea family, locoweed can grow about a foot tall with silver-gray stemmed leaves. In cattle, the weed has debilitating neurological effects that worsen as more and more is eaten.

"Worst case scenario is death, but along the way are agitated, disoriented and depressed animals with diminished reproductive capabilities," Cibils said.

Locoweed has a punishing economic effect on New Mexico's northeastern cattle country, an area internationally known for profitably stocking yearling cattle. David Graham, Union County agricultural agent with NMSU's Cooperative Extension Service, calculates the losses from diminished weight gain in yearling cattle alone at about $2 million a year in northeastern New Mexico.

The region's abundance of grasslands and top-of-the-line feedyards makes it a prime place to fatten cattle. Unfortunately, the grasslands are also a natural hot spot for locoweed. In a wet year, the poisonous plants pop up like spring tulips.

In a series of controlled experiments at NMSU's Clayton Livestock Research Center last year, Cibils, Graham and NMSU graduate student Kyle Jackson monitored locoweed intake, offered along with varying quality and quantity of other forages, on cattle that preferred locoweed and those that avoided it.

"Only a small percentage of cows will eat locoweed on first encounter," said Jackson, who saw firsthand the emotional and economic effects of locoweed afflicted cows on his parents' cattle operation near Springer. "The majority will stay away. But with time, we've seen that these natural eaters will induce the others to eat the locoweed."

During the study, researchers found a clear difference between locoweed eaters and avoiders.

"Throughout the trial these locoweed eaters ate more locoweed than those avoiders no matter what you gave them, whether it was alfalfa or wheat straw," Jackson said. "We don't know the physiological basis for this, but we do know the differences persisted no matter what was offered."

The eaters and avoiders mixed their diets differently, he said. The eaters preferred more locoweed when the other forage was low quality wheat straw. The avoiders ate very little locoweed if the other forage was bad, but were willing to eat more when other good forages were available.

"Perhaps they have different abilities for sensing the toxin," Cibils said. "But it makes sense that avoiders would eat more locoweed when the rest of the forage is good because that's when they would be getting more macro-nutrients to help them detoxify."

Controlling locoweed, especially in a sprawling pasture setting, is not a simple task, said Kirk McDaniel, a NMSU range management specialist. The weed tends to grow in clumps where the soil has previously been disturbed. Chemical treatments are available, but their effectiveness depends on a number of conditions, including cost, coverage and weather conditions.

"Typically, ranchers opt to spray only a pasture or two in order to have a locoweed-free option," he said.

This summer Cibils and Jackson will continue their locoweed project, again concentrating on the differences between cattle that eat the weed and those that give it a pass.

"Animals generally tend to stay away from new foods," Cibils said. "Are these locoweed eaters just bolder animals or are they not sensing the toxin in this weed for some reason? We need to find those answers."