Effect of age on serum concentrations of the third component of complement in dogs.

Single radial immunodiffusion was used to determine the concentration of the third component of complement (C3) in canine sera from 48 normal dogs in the following age groups: < 12 months, 12 to 24 months, and > 24 months. Mean serum C3 concentrations, expressed as the percentage of pooled reference sera from 20 dogs, showed a significant (P < 0.017) correlation with age in dogs less than 12 months old, while the character of this correlation was negative for dogs more than 24 months old (P < 0.056). Two-way analysis of variance, for age and sex, revealed significant differences between C3 values from this two groups that were not present when compared with dogs aged between 12 and 24 months old. Sex had no effect on serum C3 concentrations.