Molds, Mycotoxins and Their Effect on Horses

Dr.Kedar Karki

Background

• Pasture grasses, hay, grain, straw and stubble can all support the growth of various fungi. The fungi can exist as saprophytes, living on the outside of the plant and obtaining nutrients from the plant with no benefit to the plant, or exist as endophytes within the plant in a symbiotic relationship, providing benefits to the plant while obtaining nutrients from the plant. The saprophytes include the more common genera Aspergillus, Claviceps, Stachybotrys, Fusarium and Penicillium. The endophytes live between the plant's cell walls and include the more common genera Balansia, Epichloe, Acremonium and Neotyphodium.

Background

• Whole grain wheat is not normally fed in large amounts to horses. However, whole wheat, wheat bran and wheat by-products can be incorporated into blended horse feeds such as sweet feed and pelleted feeds. In addition, horses are commonly bedded on wheat-straw and some horses will consume a significant amount of their straw bedding.

Background• In wet harvest years, ingested DON concentrations on a total ration

basis could be significant. In the harvest year of 2000, the following results were obtained:

   * 85% (97 of 114) of wheat samples contained concentrations of DON greater than 1 ppm (mean 4.48 ppm, range 0.33 to 28.4 ppm). The zearalenone levels were of little concern, with concentrations in most cases less than 0.15 ppm. 

   * 48% of 50 samples of wheat shorts had concentrations of DON greater than 1 ppm. The mean concentration was 1.8 ppm and the highest detected was 4.6 ppm.

   * Analysis of wheat straw revealed concentrations of DON ranging from undetectable to 16.5 ppm.

Prevention and Recommendations

• Research into the effects of mycotoxins on horses is in its infancy. As a general rule, err on the side of caution.    * Feed and bed horses with hay/grain and bedding free of mycotoxins.

   * The amount of DON in cereal straw depends primarily on the presence of contaminated grain and chaff. Tedding or raking prior to baling the straw will reduce the chaff and kernels and, therefore, the concentrate of mycotoxins.

   * Since the potential concern with horses is the risk of an additive effect, in harvest years with high DON concentrations, consider limiting the use of straw bedding; ensure horses are fed high quality hay and in sufficient amounts to limit the eating of bedding.

  

Prevention and Recommendations

• * Late-gestation mares should never be allowed to consume cereal-rye straw, endophyte-infected hay or stubble or eat sclerotia-containing grain.

   * All pasture/hay seed mixes containing tall fescue and perennial ryegrass must be guaranteed endophyte-free.

   * Mow grass pastures to keep them in a vegetative state rather than letting them develop seed heads. This will minimize the opportunity for proliferation of airborne ascospore and the invasion of pasture plants.

Prevention and Recommendations

•    * Check with your laboratory. HPLC methodology may be more sensitive than thin layer chromatography (TLC) when trying to identify ergot alkaloid concentrations less than 1 ppm.

   * Mares can be treated with domperidone should an ergot alkaloid problem be suspected.

Binding Agents

•Feed manufacturers often utilize binders of various types in feeds to tie up mycotoxins. These include clay-based binders and yeast cell wall extracts (e.g., Bio-Mos-M). Raymond et al. concluded that supplementation with 0.2% yeast cell wall extract (a polymeric glucomannan mycotoxin adsorbent) improved feed intake over feeding contaminated feed alone but not when compared to control diets not containing mycotoxins (2). The long-term effects of binding agents are not clear; therefore, they should be used with caution.

References • 1. Johnson PJ, Casteel ST, Messer NT. Effect of feeding deoxynivalenol (vomitoxin)-contaminated barley to horses. J. Vet Diagn Invest 1997; 9: 219-

221.

2. Raymond SL, Smith TK, Swamy HVLN. Effects of feeding of grains naturally contaminated with Fusarium mycotoxins on feed intake, serum chemistry, and hematology of horses, and the efficacy of a polymeric glucomannan mycotoxin adsorbent. J. Anim. Sci. 2003; 81:2123-2130.

3. Barnett DT, Mowrey RA, Hagler WM Jr, Bristol DG, Mansmann RA. The correlation of selected mycotoxins to the incidence of colic in horses. World Equine Veterinary Review 1997; 3 (1).

4. Beasley VR. Equine leukoencephalomalacia/hepatosis and stachybotryotoxicosis. In: Current Therapy in Equine Medicine, 3rd ed., Philadelphia: WB Saunders, 1992: 377-380.

5. Russell MA, Eikenberry JG, Scott DH, Hope WD. Moldy corn outbreak: the Purdue CES response. Proceedings of the Equine Nutrition and Physiology Symposium 1993: 286-287.

6. Juhasz J, Nagy P, Huszenicza G, Szigeti G, Reiczigel J, Kulcsar M. Long term exposure to T-2 fusarium mycotoxin fails to alter luteal function, follicular activity and embryo recovery in mares. Equine Vet J. Suppl. 1997; 25: 17-21.

7. Juhasz J, Nagy P, Kulesar M, Szigeti G, Reiczigel J, Huszenicza G. Effect of low-dose zearalenone exposure on luteal function, follicular activity and uterine oedema in cycling mares. Acta Veterinaria Hungarica 2001; 49 (2): 211-222.

8. Asquith RL. Mycotoxicosis in horses. In: Smith JE, Henderson RS, eds. Mycotoxins and Animal Foods. CRC Press, 1991: 679-688.

9. Bacon CW. Fungal endophytes, other fungi, and their metabolites as extrinsic factors of grass quality. In: Forage Quality, Evaluation and Utilization. Nutrition Conference on Forage Quality, University of Nebraska, 1994: 318-366.

10. Lacey J. Natural occurrence of mycotoxins in growing and conserved forage crops. In: Mycotoxins and Animal Foods. CRC Press, Inc., Florida, 1991: 363-397.

11. Riet-Correa F, Mendez MC, Bergamo PN, Flores WN. Agalactia, reproductive problems and neonatal mortality in horses associated with the ingestion of Claviceps purpurea. Australian Vet. J. 1988; Vol 65, 6:192-193.

12. Wright RG, Boyce B, Van Dreumel T, Hazlett MJ, Cross DL. Ergot alkaloid toxicity in foaling mares associated with eating cereal rye straw. Abstract presented at Equine Nutrition and Physiology Symposium, Lexington KY May 28/01.

References• 13. Craig M. Personal communication. Oregon State University, Corvallis, Oregon.

14. Brendemuehl JP, Williams MA, Boosinger TR, Ruffin DC. Plasma progestagen, tri-iodothyronine, and cortisol concentrations in postdate gestation foals exposed in utero to the tall fescue endophyte Acremonium coenophialum. In: Equine Reproduction VI. Biology Reprod Mono 1, 1995: 53-59.

15. Whitwell KE , Jeffcott LB. Morphological studies on the fetal membranes of the normal singleton foal at term. Res. Vet. Sc. 1975; 19: 44-55.

16. Schlafer DH. Gross examination of equine fetal membranes: What's important - What's not! Proceedings of the Equine Symposium: Society for Theriogenology/American College of Theriogenologists, San Antonio, Texas 2000.

17. Meronuck R, Concibido V. Mycotoxins in feed. Feedstuffs 1997; July 24: 142-148.

18. Action Levels of Aflatoxin in Corn. Aflatoxin Regulations. Food and Drug Administration Release, U.S. Department of Health and Human Services; October 5, 1998.

19. Adams RS, Kephart KB, Ishler VA, Hutchinson LJ, Roth GW. Mold and mycotoxin problems in livestock feeding. PennState's College of Agricultural Sciences, Cooperative Extension note DAS 93-21: 1-16.

20. Tarr B. Molds and Mycotoxins. OMAFRA Info Article # 2. Ontario Ministry of Agriculture, Food and Rural Affairs, 1996.

21. Fumonisin Levels in Human Foods and Animal Feeds. Guidance for Industry. Food and Drug Administration Release, U.S. Department of Health and Human Services; November 9, 2001.

Author: Dr. Bob Wright -Veterinary Scientist/OMAFRA (Government of Ontario, Ministry of Agriculture, Food and Rural Affairs)