Transfer of passive immunity in foals: Can the plasma transfusion efficacy be predicted?

The treatment for failure of transfer of passive immunity (FTPI) in foals with hyperimmune plasma has substantial variability of efficacy.

The aims of the study were to assess the safety and efficacy of plasma transfusion and to investigate factors that may predict transfusion results, thereby allowing estimation of plasma volume requirements prior to transfusion.

A retrospective review was conducted of foals admitted to an equine hospital that received a plasma transfusion for FTPI.

The study included 110 foals and 150 hyperimmune plasma transfusions. The median increase in plasma IgG concentrations following transfusion (∆IgG) was 223.5 mg/dL. Among all evaluated factors (age, body weight (BW), sex, breed, year of transfusion, colostrum intake, clinical status of the foal, and time of post-transfusion IgG measurement), only pre-transfusion plasma IgG concentration, BW, and the delay in IgG measurement after transfusion correlated with transfusion efficacy (r < 0.5, P < 0.05). The influence of BW was substantial in the clinical group of healthy foals (9.17 mg/dL decrease in ∆IgG, per 1 kg increase of BW) but negligible among clinically ill foals. Foals tested within 12 h post-transfusion tended to have higher ∆IgG values, whereas no significant differences were observed between the later-time groups.

The overlapping influence of the foal-specific, technical, and biological factors precluded the identification of reliable predictors of transfusion efficacy that could be used to estimate necessary plasma volume prior to transfusion. Therefore, a timely post-transfusion evaluation of IgG is essential in clinical settings.