Prevalence of anti-red blood cel antibodies in the serum and colostrum of mares and its relationship to neonatal isoerythrolysis.

The sera of 390 pregnant Standardbred mares and 409 pregnant Thoroughbred mares were tested for anti-red blood cell (RBC) antibodies. Of the Standardbred mares and Thoroughbred mares, 20% and 10%, respectively, had anti-RBC antibodies detectable in hemolytic or saline agglutination tests. Most of the antibodies were specific for the CA blood-group antigen of horses. Other antibodies were specific for the Aa, Ab, Aa, Ab, Da, Df, Ka, Ua, or Qa blood-group antigens. The occurrence of these antibodies in the serum and colostrum was compared for 268 mares. With 3 exceptions, whenever antibodies were found in 1 sample, they were found in the other. When a mare had antibodies to the Aa or Qa blood group antigens which were reactive at serum dilutions of 1:16 or greater, colostrum was withheld from that mare's foal. This practice seemed justified, because 1 foal which accidently received colostrum with anti-Aa antibodies developed neonatal isoerythrolysis. All other foals were allowed to nurse their mares' colostrum. None of them developed neonatal isoerythrolysis, even when anti-RBC antibodies were found for blood-group antigens other than Aa or Qa which reacted with the foals' RBC in in vitro tests.