Randomized, controlled trial comparing Rhodococcus equi and poly‐N‐acetyl glucosamine hyperimmune plasma to prevent R equi pneumonia in foals

Background Hyperimmune plasma raised against β‐1→6‐poly‐N‐acetyl glucosamine (PNAG HIP) mediates more opsonophagocytic killing of Rhodococcus equi (R equi) than does R equi hyperimmune plasma (RE HIP) in vitro. The relative efficacy of PNAG HIP and RE HIP to protect foals against R equi pneumonia, however, has not been evaluated. Hypothesis Transfusion with PNAG HIP will be superior to RE HIP in foals for protection against R equi pneumonia in a randomized, controlled, blinded clinical trial. Animals Four hundred sixty Quarter Horse and Thoroughbred foals at 5 large breeding farms in the United States. Methods A randomized, controlled, blinded clinical trial was conducted in which foals were transfused within 24 hours after birth with 2 L of either RE HIP or PNAG HIP. Study foals were monitored through weaning for clinical signs of pneumonia by farm veterinarians. The primary outcome was the proportion of foals that developed pneumonia after receiving each type of plasma. Results The proportion of foals that developed pneumonia was the same between foals transfused with RE HIP (14%; 32/228) and PNAG HIP (14%; 30/215). Conclusions and Clinical Importance Results indicate that PNAG HIP was not superior to a commercially available, United States Department of Agriculture‐licensed RE HIP product for protecting foals against R equi pneumonia under field conditions.