tall fescue toxicity and management

what causes tall fescue toxicosis

Ergot alkaloids produced by a fungal endophyte.

What is fescue foot?

Vasoconstriction causing poor circulation, tenderness, gangrene, and possible loss of hooves, ears, or tail portions.

When is fescue foot most common

Winter, especially in the Upper South.

What is bovine fat necrosis?

Hard masses of fat in the abdominal cavity that may cause digestive problems and dystocia.

What is summer slump or fescue toxicity

Poor weight gain, reduced conception, heat intolerance, failure to shed winter coat, and elevated body temperature.

When is summer slump most evident

during warmer temperatures.

What reproductive problems can toxic tall fescue cause in horses

Abortions, prolonged gestation, dystocia, thick placenta, foal death, retained placenta, and agalactia

What is agalactia

failure to produce milk

How do cattle respond behaviorally to toxic fescue

Spend more time in shade and water and less time grazing

What physical signs can cattle show from fescue toxicosis

Thin body condition, rough hair coats, and mud-caked appearance

How does toxic fescue affect animal performance

50–100% reduction in gain, about 30% lower milk production, and reduced conception rates, potentially as low as 50%

How does the tall fescue endophyte reproduce and spread

spreads only through infected seeds

What happens to endophyte viability in stored seed

It declines quickly because the endophyte is fragile

What toxic compounds does the endophyte produce

Ergot alkaloids

How does the endophyte benefit tall fescue?

Improves drought tolerance, root development, tillering, water efficiency, nitrogen utilization, and resistance to insects and nematodes

How does the endophyte affect tall fescue palatability

it reduces it

What does tall fescue gain from its symbiotic relationship with the endophyte

Greater persistence and survival under stressful conditions

What does the endophyte gain from tall fescue

Nutrients and a mechanism for reproduction

What is endophyte-free tall fescue

Tall fescue containing no endophyte; improves animal performance.

How can endophyte-free tall fescue seed be produced?

Moderate seed heating, fungicide treatment, or storing seed for a year.

What are the disadvantages of endophyte-free tall fescue?

Reduced persistence, more difficult establishment, and greater need for careful grazing management.

How does removing the endophyte affect grazing and stocking?

Increases palatability and intake; may require reduced stocking rates

What is novel endophyte tall fescue?

Tall fescue containing an endophyte strain that does not produce toxic alkaloids.

Why is novel endophyte tall fescue beneficial?

Improves animal performance while retaining plant vigor, pest resistance, drought tolerance, and grazing tolerance.

How can toxic endophyte-infected fescue be reintroduced to clean pasture?

Through contaminated hay, seed, or equipment.

How long should animals be held before entering endophyte-free or novel endophyte pastures?

72 hours.

What minimum residue height is recommended for endophyte-free or novel endophyte fescue?

4 inches.

What should a producer determine before choosing a toxic-fescue management strategy?

The pasture's endophyte infection level.

Why should toxic tall fescue be avoided during warm weather?

Endophyte toxins have greater adverse effects during warm temperatures.

When are toxin levels typically highest in tall fescue?

late spring, with a smaller peak in late summer or autumn.

How can the toxic effects of tall fescue be diluted?

Include legumes, other grasses, warm-season forages, hay, or grain.

How can legumes improve animal performance on toxic fescue?

Dilute toxins and provide biochanin and isoflavones that enhance performance.

What grasses can help dilute toxic tall fescue?

Kentucky bluegrass, orchardgrass, bermudagrass, and crabgrass.

Why should nitrogen fertilization be used carefully on toxic tall fescue?

Nitrogen is a component of the toxic alkaloids.

Why should tall fescue seedhead consumption be reduced?

Seeds are highly toxic and may be selectively grazed.

How can seedhead exposure be reduced?

Graze closely enough to limit seed production or mow seedheads.

What is stockpiling tall fescue?

Allowing forage to accumulate after late-summer grazing or clipping for later use during cooler months.

Why does stockpiling help reduce tall fescue toxicity?

Toxin levels decline over time, and animals consume the forage in cooler weather.

Why can feeding tall fescue hay reduce toxicity compared with grazing?

Toxin levels are lower in hay, often fed during cooler months.

What is a disadvantage of feeding toxic tall fescue hay?

It can spread toxic endophyte-infected seeds.

What medication can help prevent foaling problems in mares exposed to toxic fescue?

Domperidone

Why is domperidone not a common solution for cattle?

It is not cost-effective for cattle.

At what infection level is renovating toxic tall fescue recommended?

60% or greater endophyte infection.

What is the main disadvantage of renovating toxic tall fescue?

It is expensive, and all existing toxic endophyte-infected fescue must be destroyed.

What is the spray-smother-spray method?

A renovation method using herbicide, a summer cover crop, another herbicide application, then planting novel endophyte fescue.

What are the steps of spray-smother-spray?

1. Prevent seed production. 2. Apply herbicide in spring. 3. Plant a summer annual cover crop. 4. Destroy the cover crop and spray again. 5. Plant novel endophyte fescue.

Why should seed production be prevented during the renovation year?

To prevent toxic tall fescue from reestablishing through its seeds.