Effects of an Immunostimulant Containing Propionibacterium acnes (EqStim) on Cell-Mediated Immunity and Nasal Shedding of Respiratory Pathogens Using a Model of “Weaning” Stress in Foals

• Weaning of foals is a stressful event and has been shown to reduce cell-mediated immunity (CMI).
• The immunostimulant Propionibacterium acnes is thought to enhance CMI.
• Regardless of immunostimulant (EqStim) treatment, foals experienced significant changes in clinical and immunologic measures after weaning.
• Treatment with EqStim modulated rises in serum cortisol concentrations and increased some measures of innate immunity after weaning of foals.

Weaning of foals is a stressful event, and often, times can be associated with negative health consequences, including reduced immunity and increased susceptibility to gastrointestinal and respiratory disorders. Thus, a possible preventative immunomodulator of weaning-associated stress was studied in 21 pony foals (205 days ± 5 day old). Of these, n = 11 received the immunostimulant EqStim and n = 10 received a saline control on days −7, −3, and 0 (day of weaning). During these time points, as well as days 3, 7, 14, and 21, after weaning measurements were determined for the following parameters: clinical parameters as well as plasma cortisol concentrations, immune function using flow cytometry for protein determination and real-time polymerase chain reaction (PCR) for gene expression, and pathogen detection using nasal swabs (NSs) and PCR. Results showed an overall time effect of weaning for most parameters: decreased rectal temperature, increased nasal discharge and NS PCR detection of Streptococcus equi subsp. zooepidemicus, increased serum cortisol levels, and both decreased and increased production of cytokines (lymphocyte production interferon gamma and tumor necrosis factor alpha (TNF-α) and whole blood levels of IL-1β, TNF-α, and IL-10). In addition, there was an effect of treatment on cortisol concentrations and peripheral blood mononuclear cell production of IL-1β. Data suggest that, regardless of treatment, the weaning process produces significant changes in clinical and immunologic measures in foals. Although treatment with the immunostimulant EqStim had no effect on the incidences of nasal shedding of respiratory pathogens or other clinical parameters, it did appear to modulate rises in cortisol after weaning and possibly enhance innate immunity.