Sixty Thoroughbred foals were divided into two groups according to the occurrence of clinical signs. Their sera Immunoglobulin (Ig) levels were evaluated from 3 hours up to 6 months of age. The ZST-test using either spectrophotometer or naked eye was a good indicator of Ig concentration determined by electrophoresis. Serum Ig decreased at the end of the first month both in healthy and sick foals, rising again after one to two weeks. This may indicate the passage from passive to own immune response. Minimal sera Ig levels of 400mg/dl suggested elsewhere is not compactible with healthy foals in this work. It is suggested here to set a new minimal level at 800mg/dl. This would be considered the minimal exigence when evaluating high risk foals, but should not be analised alone; there are strong evidences that husbandry measures and environmental conditions might play important roles in the process.
foal; immunoglobulin; immunity
