Pasture Samples Stress Dangers of Tall Fescue Toxicosis

Comparing pasture samples from 2002 and 2003 didn't associate Mare Reproductive Loss Syndrome with anything other than the Eastern tent caterpillar. However, Wayne Long of the University of Kentucky's Department of Agronomy provided some insight on pasture management in Central Kentucky and stressed the dangers of tall fescue toxicosis. He presented field study results on pastures to a group of veterinarians and students on Jan. 20 at UK's Gluck Center.

In 2002, more than 3,000 samples were analyzed for factors that could be attributed to MRLS, compared to 1,224 in 2003. There were 38 confirmed fetal losses (29 early fetal losses and nine late fetal losses on six farms) attributed to MRLS in 2002, and no losses attributed to MRLS on farms that were selected for analysis in 2003. Nine farms in 2002 were examined on an emergency basis (veterinarians or farm owners observed losses and requested sampling) compared to five in 2003. Compared to 30 losses in 2002, there were only three in 2003--one was a suspected late fetal loss, and two were probably associated with fescue toxicosis, said Long.

There were no apparent health problems associated with any slight changes of nitrate and potassium/calcium ratios in pastures between 2002 and 2003. There was significantly more white clover in 2003 than in 2002 pastures, probably due to increased rainfall early in the year.

White clover covered more than 80% of some pastures in 2003, but no losses were attributed to possible cyanide poisoning from this plant.

Fescue often contains a fungal endophyte that can have highly deleterious effects--it is associated with agalactia (no milk production), dystocia (difficult birth), long gestations, thickened placentas, and weak or dead foals. "What I've been drawn to mostly is fescue in horse pastures," said Long. "This fungus has a wonderful relationship with tall fescue. It helps reduce insect damage, aids in drought tolerance, and improves grazing tolerance by livestock."

Long has seen up to 60-65% fescue coverage in barren or maiden mare pastures. If not carefully managed, tall fescue can take over a pasture in just a few years. It is not the forage of choice for horses, so when they've eaten everything else, fescue aggressively takes over the bare patches.

"The field data really give us a better understanding of how safe equine pastures in Central Kentucky are," he said. "It's helped develop a model for recommendations to the equine industry (for pasture management). Additional work is needed to further understand the complex relationship between tall fescue and the horse. There's so much more that can be learned with fescue toxicosis and animals."

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