Evaluation of a series of testing procedures to predict neonatal isoerythrolysis in the foal.

A series of modified (field) tests were compared to a crossmatch between mare and foal for their reliability in predicting neonatal isoerythrolysis (NI) in eight foals born to experimentally alloimmunized mares. In the field tests, mare's serum, plasma and colostrum were combined with foal erythrocytes washed by a modified procedure to determine which combination was the best predictor of impending NI. A consistent grading system for agglutination and hemolysis was employed. The field tests using mare's plasma demonstrated less agglutination and hemolysis than tests where serum was employed. Immediate assessment of agglutination failed to demonstrate agglutinin activity when compared to tests where incubation was included. Rouleaux formation posed a problem in interpretation of minor agglutination, however the grading of hemolysis was simpler, quicker, and more accurate. The field test that was most reliable when compared to the crossmatch and presuckle anti-foal erythrocyte titers in demonstrating agglutinins was the combination of mare's serum and foal's erythrocytes. The tests for hemolysin detection in serum and colostrum which incorporated rabbit sera as a complement source were also reliable.