Immunostimulants for Foals

A product that could stimulate the immune systems of newborn foals to better fight infection of Rhodococcus equi would be very beneficial, said Steeve Giguère, DVM, PhD, of the University of Florida, at the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif.

Pneumonia caused by R. equi is endemic on many farms, he said. Studies have shown that immunostimulants decrease the incidence of respiratory disease, but there is no data looking specifically at R. equi-caused respiratory disease.

The researchers, Giguère said, hypothesized that immunostimulants can enhance immune system cells' ability to kill R. equi.

Seventeen foals were involved in the study, and they received Zylexis (a commercial immunomodulator offered specifically as an aid for reducing upper respiratory disease caused by equine herpesvirus-1, or EHV-1, and EHV-4), EqStim (a commercial immunostimulant), or saline. Blood and bronchial lavage (BAL) cells were collected on Days 7 (pre-treatment), 19, 31, and 43. The cells of the foals were infected in vitro with R. equi.

The researchers reported: "Neutrophils from foals treated with inactivated parapoxvirus ovis (Zylexis) had significantly greater ability to phagocytize (engulf) R. equi and undergo oxidative burst on Days 19 and 31 compared to baseline values. On Day 31 foals treated with inactivated parapoxvirus ovis had significantly greater phagcytosis and oxidative burst than foals treated with inactivated Propionbacterium acnes (EqStim). In contrast, treatment with EqStim resulted in significantly less intracellular proliferation of R. equi within blood-derived macrophages (R. equi multiplied less within types of white blood cells that ingest foreign material) compared to control foals, but not compared to foals treated with Zylexis."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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