On the cow side of the pasture/livestock equation, in many cases we are looking at some mighty hungry individuals. Hay is scarce and expensive, and concentrates are higher than many of us can remember them ever being.

This has led many producers to design a management program to “get ’em through the winter” rather than meeting the cattle’s nutritional requirements.

Under good growing conditions the primary plants have no trouble holding their own, but under poor or marginal conditions of soil fertility and moisture, the less-desirable species become much stronger competitors.

Additionally, in many of these pastures some of the perennial grasses and forbs have died, leaving a vacuum that undesirable species may well fill.

Many of these undesirable species have the potential to be toxic to livestock if consumed in sufficient quantities.

Nature’s normal defense against toxicity problems is that most toxic plants have very poor palatability and are not usually consumed if more desirable forage plants are present in adequate supply.

In our current scenario, however, along comes old mama cow. After months of not having her dry matter intake requirements met, she is just looking for anything that will satisfy her hunger, and under the circumstances it may be toxic species that she would not ordinarily choose to consume.

There are a wide variety of plants with toxic potential in Oklahoma pastures. Many of them we don’t think of as toxic because they don’t usually cause problems under normal circumstances, but the potential is there.

Several different plants can cause gastrointestinal upsets, including oleander, ivy, iris, pokeberry, wisteria and mistletoe. Lupine causes breathing difficulty.

Mushrooms can cause gastrointestinal upset and breathing difficulty. Oak leaves and shoots, under certain conditions, can cause kidney damage which may not show up until weeks or months after the toxin is ingested. Oral irritation is caused by ingesting poison ivy, poison oak, rosary pea and castor bean.

There are many other plants that have the potential to cause toxicity. Some of these would be cockle burr, red maple, common yarrow, wild onion, Indian hemp, milk weed, aster, beggersticks, musk thistle, larkspur, curly dock, nightshades and death camas.

This is by no means a complete list and the species found in your area will vary greatly. If in doubt, enlist the help of your local veterinarian or take a sample of suspect plants to your county extension office for identification.

It is impossible to eliminate all risk from plant toxicity, especially during the spring green-up, but the following practices can help minimize risk and cut losses.

• Don’t overgraze.
• Do not introduce cattle to new pastures while they are hungry. Give them a chance to fill up on good palatable hay so they start to graze selectively.
• Turn a few older, low-value individuals into new areas first. If they experience no difficulty, follow a day later with their herdmates.
• Spend time with your cattle and note what they are eating. If you don’t recognize the plants, have them identified by someone who can help.
• Watch closely for diarrhea, rapid breathing, staggers or other signs of distress. If you observe these signs early and move affected animals to another pasture, many of them will recover uneventfully.

As a cattle producer today, you have plenty to worry about with the drought and high input costs for feed, fuel and fertilizer. Don’t let toxic plants cull your herd the hard way. 

Dave Sparks is a veterinarian in the Oklahoma State University Extension area.

—Excerpt from Cow/Calf Corner e-newsletter