A modified zinc sulfate turbidity test for the detection of immune status in newlyborn foals

Abstract

The accuracy of a modified zinc sulfate turbidity test, in estimating a serum IgG concentration of 400 mg/dl, was evaluated. Sera from 161 foals <18 hours of age were incubated for 15 and for 60 seconds with zinc sulfate. Turbidity was assessed both visually, in a veterinary practice and a laboratory, and with a spectrophotometer. Serum IgG concentration was determined by single radial immunodiffusion assay. Twenty five of the 161 foals (15.5%) had <400 mg of IgG/dl of serum. Failure of passive transfer (serum IgG concentration <400mg/dl) was correctly identified visually in 21 of the sera (84%) in the laboratory, and in 20 of the sera (80%) in the veterinary practice. Spectrophotometric values (light transmittance 550 nm) from zinc sulfate assays were inversely proportional to the serum IgG content (r= −0.88; p<0.0001). Serum containing <400 mg/dl transmitted >80% light. Evidence of adequate passive transfer was detected visually in 100% of the samples (136 serum samples) and 96% of these samples transmitted <80% light (131 of 136). Seventy four percent of those foals sampled by 10 hours after foaling had >400 mg of IgG/dl. The modified zinc sulfate turbidity test detected accurately all foals with failure of passive transfer when sera was assessed visually and by spectrophotometer. Serum containing <400 mg of IgG/dl had no precipitate or slight precipitate and transmitted >80% light.