Evaluation of acquired passive immunity in mule foals up to 60 days of age.

Ten mule foals were used to investigate serum IgG concentration. Blood was collected from mares and foals on the day following parturition (D1), at 48 and 72 hr after birth (D2 and D3), and on D7, D14, D21, D28, D35, D42, and D60. Serum IgG concentration was determined by zinc sulfate turbidity test and was above 400 mg/dl at all time points, except for one foal on D2. Mean values were above 800 mg/dl from D1 to D7 and at D60. The difference between mares and foals at each collection time was significant, except at D1. For all other days, foal IgG values were lower than the mare IgG values. Mean IgG concentrations were lower from D14 to D42 compared with D1 and D60. The results show that the critical period for the mule foal is at D28, which can be a vulnerable window for infections. The variation pattern in IgG values is similar to that in data published for horse and donkey foals. There are no published studies to date on the subject, and the present contribution enables further understanding of the newborn mule foal.