Forage Management

Toxic Fescue Time Bomb

Victoria G Myers
By  Victoria G. Myers , Progressive Farmer Senior Editor
One ill-timed nitrogen application can increase toxins in tall fescue, setting back herd health and reproduction. (DTN/Progressive Farmer photo by Mark Parker)

Craig Roberts doesn't just think toxic fescue negatively affects health and reproduction in beef herds across the South, he knows it does. There is no such thing as a herd of cattle that has completely acclimated to ergot alkaloids, despite what it may look like.

Roberts, a forage specialist with the University of Missouri, noted there are plenty of anecdotal stories about herds that have become resistant to the toxins in Kentucky 31. However, he said when these animals are studied, the reality doesn't match the perception.

"Many times, we hear people say their cattle have adapted to toxic tall fescue. They've had the cattle so long and culled them so well that they believe the herd is not affected. I can tell you with 100% certainty that is untrue," Roberts stressed.

He has worked in the field of toxicosis for 37 years and says they have tested more than 3,000 head. Of those, Roberts says 15 to 20% are at best tolerant to the toxin, but not resistant. Another 15 to 20% are highly susceptible.

Negative responses to the toxin make a lengthy list. Start with gains. Roberts said researchers have reported as much as a 50% loss of gain in steers when pastured on a high-endophyte fescue. Other issues include diminished milk and colostrum production, lower weaning weights, aborted fetuses, fescue foot, higher internal body temperature and respiration rates, rough hair coats and lower calving rates. These symptoms were not uncommon in cattle that hadn't "fallen apart," as common vernacular would describe an animal that has an obvious negative reaction to the toxin.

"When we look at these cattle that are allegedly adapted, while there is variation, we still note poor performance," Roberts stressed.

He added if animals do "adapt" to the toxin, it's a temporary condition at best. He explained when cattle are moved to novel endophyte fescue, or nonfescue pastures, they lose any temporary tolerance, becoming "naive" after a couple of months.

Nitrogen Applications.

One reason there is still so much Kentucky 31 across the South is the expense of converting pastures. There are also concerns about the hardiness of novel endophyte varieties. Roberts noted there are effective strategies to minimize toxin levels in toxic tall fescue, beginning with a well-planned approach to nitrogen application.

Nitrogen, he explained, is key in the development of secondary metabolites, or toxins, in tall fescue. Nitrogen feeds the fungus that makes the toxin.

"The plant uses nitrogen first to meet its primary function needs, which are leaf growth and then root growth. After that, remaining nitrogen goes to these secondary metabolites," he explained. The goal is to have as little nitrogen available as possible for that secondary function.

There are three primary options when it comes to fertilizing Kentucky 31, Roberts explained. Producers can apply nitrogen in the spring if they plan to cut the forage for hay before seed heads emerge. This is critical to note, as late-baled hay with seed heads will be toxic and lower in nutrients.

A late-summer to early-fall nitrogen application is another option. This will boost autumn growth providing the option of grazing through October or stockpiling. Roberts cautioned not to exceed 40 to 50 pounds of nitrogen per acre, or toxin levels can skyrocket.

The last alternative is to interseed clovers with the toxic tall fescue. In some cases, this allows producers to skip the nitrogen application altogether, as the legumes will fix free nitrogen. There remains a need to monitor soil pH, however, and apply P (phosphorus) and K (potassium), as needed.

"If you're looking at a grazing-only, rotational system where manure is distributed evenly, this is probably a scenario where you may eliminate the need to apply nitrogen completely," he added. "If I'm going to cut hay, though, I need a little nitrogen in the spring. Too much can crowd out legumes, so be conservative."

Lastly, Roberts recommended testing soils every four to five years. He noted when fields are clipped for hay, it's important to remember nutrients are being removed, and they need to be replaced to maintain productivity and nutritional values.

(AG)

Victoria Myers