Mesquite bean poisoning in cattle

Sep 23, 2011

“Son, don’t get rid of all your mesquite . . . The beans might keep your cows fat when there’s a drought.”

Timely advice considering the current ‘powder on packed powder’ appearance of Texas’ pastures with conditions so dry a cowboy could ride a sand surfboard around his country checking fence lines. These days, the only green on the scene is located in bar ditches or within the vast thickets of overgrown mesquites that have made a good stand this summer.

Mesquite is abundant in the southwestern U.S. Mesquites are thorny bushes or trees with fibrous beans and are among the most predominant invasive native plants in that region. They are drought and heat resistant, thrive on all soil types, and have a tap root system to locate subterranean water.

The plant competes with desirable forage species for water, light and nutrients. Sixty years of efforts to control mesquite with fire and by mechanical and chemical means have not significantly altered the prevalence and spread of this brush.

Parts of Texas are having a bumper crop of mesquite this droughty year with some plants having a third bloom. Usually, mesquite beans are readily consumed by cattle, sheep, goats and horses that may also eat the dry beans off of the ground. In most years, the beans can be a valuable addition to grazing and browsing diets. Mesquite beans are not a complete feed for cattle as they cannot reasonably meet their need for dietary fiber without causing problems. But when the mesquite augment pasture forage, cattle do well on them and the beans can be a significant contributor to their nutrition.

Mesquite beans are high in carbohydrates and are an energy source. About 15 percent of the beans are seed which contains most of the protein and fat. The remaining 85 percent of the bean, the pod, contains the majority of the fiber and sugar.

Green mesquite beans are about 50 percent moisture and the moisture content of dried beans on the ground is about 1 percent. Protein concentration varies from 28 percent in young beans to 12 percent at maturity. During this growth phase, increases in both fat (2-3 percent) and fiber (17-30 percent) occur.

The ‘good part that comes with the bad part’ of this nutritional picture is the high amount of sugar in mesquite beans: 65-80 percent. That sugar content is a key player in mesquite bean toxicity when accompanying dry matter intake of pasture forage or hay becomes limited in drought conditions like the one Texas is dealing with this year.

Mesquites produce more beans in time of drought and their beans can help sustain animals during these conditions. However, the same set of circumstances that links drought to a great mesquite bean crop can also create problems for cattle.

Problems arise for cattle when they eat mesquite beans continuously, making up more than 60 percent of their diet, for 60 days or longer in pastures lacking grass or browse. Overconsumption of beans with minimal roughage creates mesquite bean toxicity for some cattle resultant in severe weight loss and other long term affects. They become poor doers and can eventually die. This toxicity is seen more commonly in late summer and early fall.

Overconsumption of beans results in digestive changes within the rumen which can eventually lead to a specific neurologic dysfunction of cattle when they attempt to prehend, chew and swallow their food. What begins as a nutritional problem evolves into a toxicity syndrome.

Digestive problems from overconsumption of mesquite beans occur when disproportionate amounts of beans are fermented in the rumen. The high sugar content in this increased volume of beans creates a rumen acidosis killing the majority of normal microflora necessary for cellulose digestion. This ongoing chronic rumen acidosis inhibits digestion of the high fiber content of the beans. With decreased digestion, the cattle essentially starve. Decreased rumen motility due to the chronic acidosis also can lead to rumen impactions that contain a mass of seeds and pods.

Affected cattle develop poor appetites. Rapid, severe weight loss and ill thrift are the most apparent signs and can be seen within 30 days after overconsumption of the mesquite beans. These cattle become poor doers and it is not uncommon for cattle to lose up to 50 percent of their body weight within a short period of time.

The cattle that survive the ‘Do or Die’ chronic rumen acidosis phase of mesquite bean toxicity progress to neurologic deficiency problems associated with this disease syndrome. Cattle that have overconsumed the beans the previous fall can manifest symptoms the following winter.

An unidentified toxin in the mesquite bean selectively causes an impairment of nerve functions necessary for eating. The toxin found in these beans has a novel pathogenesis, characterized by a selective, primary and progressive injury to the neurons of the trigeminal and other cranial nerves involved with cattle’s prehending, chewing and swallowing.

These cattle gradually develop jaw muscle atrophy, malfunction and protrusion of the tongue, profuse salivation, oral impactions, continuous chewing and a slack mandible. If affected cattle are in the first stages of the disease, removed from access to mesquite and then placed on a high quality ration, there is a possibility for improvement, but recovery is still minimal. Treatments that have been attempted include B vitamins and inoculation of the rumen of affected cattle with normal microflora obtained from a healthy or slaughter animal; but it’s generally not time or cost efficient. Advanced stages of mesquite bean toxicity carry an extremely poor prognosis and cattle gener ally waste away and die.

This problem usually affects about 80 percent of a herd.

Insofar as other livestock are concerned, goats are fairly resistant to mesquite bean toxicity. The beans apparently do not affect sheep.

Horses garnishing the nutritional benefits found in mesquite beans are only susceptible to mesquite bean impactions of the intestine. These impactions from eating large quantities of beans can result in colic which is usually resolved with medical treatment and rarely requires surgery to remove the mass of beans.

If owners of a dehydrated ranch can take any solace when seeing an overgrowth of mesquite on their place, it may be in the fact that those thickets are providing some groceries to their cattle to help them through these hard times. Still. it must be remembered: Beans good forage = fat cows. Lots of beans plus very poor forage = skinny cows.

The question remains when seeing a skinny cow that’s in a dried up pasture with mesquites:

Is she skinny because of mesquite bean toxicity, or is she skinny because she has to graze in a dried up pasture, or is she skinny because of the frazzlin’ heat this year, or is she skinny because all the other factors that drought brings to the table . . . Or all of the above. Hard to pick the right answer when the drought has thrown a lot of curve balls at ranch management this year. —Ginger Elliot, WLJ Correspondent