1a.Objectives (from AD-416)
The overall objective of this research is to minimize economic losses from fescue toxicosis. Specific objectives include:. 1)development of plant germplasm that is both non-toxic and persistent, which could involve germplasm infected with novel endophytes or germplasm that is endophyte-free;. 2)development of management practices that improve animal performance and reduce effects of heat stress associated with fescue toxicosis in animals;. 3)further evaluation of fescue toxicosis effects on animal physiology and recovery from this condition; and. 4)identification of markers of animal sensitivity to heat stress and fescue toxicosis.
1b.Approach (from AD-416)
Tall fescue, infected with endophytes that do not produce animal toxic alkaloids, will be tested for animal toxicosis in feeding and grazing trials. Persistence of new germplasms will be measured in grazed pastures. Forage management practices will be developed to control and reduce toxicity of tall fescue. Endophyte-free germplasm with increased concentrations of plant proteins associated with nematode resistance will be tested for persistence. New approaches to monitor body temperature will be established and used to evaluate techniques for reducing heat stress. Treatments that promote healthy immune systems, like antioxidant activity and body temperature regulation, will be assessed for effects on severity of fescue toxicosis under field and in climate-controlled environmental chambers. Genetic and physiological markers of animal sensitivity to heat stress and fescue toxicosis will be identified to improve selection of animals that are more resistant to these problems.
Cattle raised for generations on endophyte-infected tall fescue (E+) may have an acquired tolerance to fescue toxicosis. This can be tested using the same cattle breed from different US regions where E+ is present (Missouri) or absent (Oklahoma). Angus steers from Missouri (MO ANG) and Oklahoma (OK ANG) were fed a diet containing either E+ or uninfected tall fescue seed in the Brody Environmental Center at the University of Missouri. During heat stress, both groups exhibited a feed intake reduction, with OK ANG averaging a greater decrease than MO ANG. Although there appear to be large differences in feed intake response to heat stress that are related to region of origin, there are no differences in the thermoregulation response to fescue toxicosis. Origin of cattle should be taken into consideration when livestock producers are purchasing replacement animals.
Heat-sensitive Angus steers (ANG) from Missouri (MO) and Oklahoma (OK) were tested with the heat-tolerant Romosinuano breed (RO) from Florida in the Brody Environmental Chambers at the University of Missouri. Angus from MO displayed more thermal flexibility when compared to OK, since they live in a more climactically diverse environment. RO share similarities with both groups of ANG and can withstand high environmental temperatures due to increased heat loss. Beef producers should be aware of specific breed differences in regards to heat tolerance when selecting breeds for certain environmental conditions.
A multi-year study was completed that evaluated potential effect of endophyte on persistence through the winter months; the findings showed that endophyte status has no effect on cold tolerance of the grass, which is apparently controlled by the genotype. Another multi-year study was completed that evaluated the effect of bermudagrass pastures in a tall fescue grazing system; the findings indicate that systems with bermudagrass result in much higher steer gains until early September; during the fall months, steers without bermudagrass catch up to those coming from bermudagrass to toxic tall fescue.
ADODR monitoring of this project was accomplished by frequent emails and telephone calls between the ADODR and University of Missouri scientists.