Ability of a commercial feed additive to modulate expression of innate immunity in sheep immunosuppressed with dexamethasone

In the first study, we tested the ability of a commercial feed additive (OmniGen-AF) to affect markers of innate immunity in immunosuppressed sheep and the ability of a pathogen challenge (mould) to affect the immune response to the additive. Treatments consisted of (1) control, (2) immunosuppressed with dexamethasone (DEX), (3) immunosuppressed plus the feed additive, (4) immunosuppressed plus Aspergillus fumigatus and (5) immunosuppressed, A. fumigatus and the additive. Animal health was monitored and indexes of innate immunity (neutrophil L-selectin and interleukin-1b (IL-1b)) were collected. DEX caused immunosuppression (i.e. reduced abundance of neutrophil L-selectin and IL-1b). This immunosuppressive effect was countered by the provision of the additive in the ration. Provision of mould in the ration increased the ability of the additive to regulate markers of innate immune function. A second study was completed to re-assess the properties of the additive and other feed products. The study consisted of seven treatments: (1) immunosuppressed, (2) immunosuppressed with additive, (3) immunosuppressed with additive in pelleted form (low-temperature pellet) and (4) immunosuppressed with additive in a high-temperature pellet. The remaining three treatments assessed abilities of three other additives to regulate markers of innate immune function. In this study, OmniGen-AF increased expression of neutrophil L-selectin abundance in immunosuppressed animals and this was unaffected by the pelleting temperature. None of the other additives affected markers of innate immunity. In these studies we discovered mechanisms by which a feed product may affect the immune function of ruminant livestock. The product countered DEX-dependent down-regulation of markers of innate immune function and its actions were enhanced by the presence of pathogen (mould) in the ration.