Equine fescue toxicosis: signs and solutions

Abstract

Gravid mares grazing endophyte-infested (E+) tall fescue exhibit increased gestation lengths, agalactia, foal and mare mortality, tough and thickened placentas, weak and dysmature foals, increased sweating during warm weather, reduced serum prolactin and progesterone, and increased serum estradiol-17 beta levels. Also, E+ tall fescue hay is less digestible than endophyte-free (E-) hay. Unlike many other species, horses consuming E+ tall fescue do not exhibit increased body temperature. Young horses consuming only E+ pasture do not gain as well as those consuming E- pasture. There is little difference in gain when the pasture is supplemented with enough concentrate to meet NRC requirements for growth. Neither selenium injections nor supplementing with corn at 50% of the NRC requirements for energy reduces the effects of toxic tall fescue on reproduction and lactation in gravid mares. It seems that the alkaloids of E+ tall fescue are serving as D2 dopamine receptor agonists. This activity would explain their prolactin-lowering effect. Domperidone, a dopamine receptor antagonist, is effective in preventing the signs of tall fescue toxicosis in horses without neuroleptic side effects.

Elimination of ergovaline from a grass– Neotyphodium endophyte symbiosis by genetic modification of the endophyte

“…Livestock maladies associated with ergovaline consumption (''tall fescue toxicosis'') include poor weight gain, hormonal imbalances leading to reduced fertility and lactation, and gangrene of the animals' limbs (12)(13)(14)(15). The economic magnitude of tall fescue toxicosis in the U.S. can be gauged by an estimated $600 million loss to the beef cattle industry during 1990 (16).…”

Correlation of Ergovaline and Lolitrem B Levels in Endophyte-Infected Perennial Ryegrass (Lolium Perenne)

“…Fescue foot, fat necrosis, and equine reproductive problems have also been reported. 7,8,20,22 Although it is generally accepted that endophyte-infected perennial ryegrass contains both ergovaline and lolitrem B, 4 only the clinical signs of staggers associated with lolitrem B are observed in animals ingesting endophyte-infected perennial ryegrass.…”

Correlation of Pituitary Histomorphometry with Adrenocorticotrophic Hormone Response to Domperidone Administration in the Diagnosis of Equine Pituitary Pars Intermedia Dysfunction

“…25 A test that is based on dopaminergic regulation of the PI, rather than the hypothalamic-pituitaryadrenal axis, is needed to evaluate the PI function in horses without hirsutism. Domperidone, a synthetic benzimidazole that is approved for treating endophyte-associated agalactia in mares, 10 specifically blocks peripheral dopamine D2 receptors. 5,8 In the PI, this releases melanotrophs to express POMC-derived peptides, including a-MSH, bendorphin, corticotrophin-like intermediate peptide (CLIP), and ACTH.…”