The development of a dexamethasone challenge model for evaluating feed additives in sheep

Area of Science:

• Animal immunology
• Ruminant nutrition
• Feed additive efficacy

Background:

• Developing reliable in vivo models for assessing feed additives in ruminants is crucial for animal health and productivity.
• Dexamethasone (Dex) is a potent immunosuppressant that can be used to create immune challenge models in livestock.

Purpose of the Study:

• To establish an accessible ruminant immune challenge model for rapid in vivo evaluation of feed additives.
• To assess the efficacy of specific feed additives in mitigating Dex-induced immunosuppression in sheep.

Main Methods:

• Sixty ram lambs were used, divided into four treatment groups: control, immunosuppressed control, immunosuppressed with yeast/botanical extract, and immunosuppressed with aluminosilicates/yeast components.
• Immunosuppression was induced using twice-daily dexamethasone injections.
• Sheep were immunized with keyhole limpet hemocyanin (KLH) and challenged with aggregated KLH to assess immune response via skin induration.

Main Results:

• Dexamethasone treatment reduced body weight, average daily gain, lymphocyte percentage, red blood cell count, hemoglobin, hematocrit, and skin induration.
• Feed additives did not mitigate the reduction in body weight and average daily gain caused by Dex.
• However, feed additives mitigated the immunosuppressive effects of Dex on hematocrit, hemoglobin, red blood cell count, and skin induration diameter.

Conclusions:

• The developed model effectively simulates immunosuppression in ruminants using dexamethasone.
• This model serves as a valuable tool for evaluating the potential of feed additives to counteract immunosuppressive effects in livestock.
• Specific feed additives demonstrated efficacy in mitigating certain hematological and immunological impacts of dexamethasone-induced immunosuppression.