Information on aging and the innate immune response in dogs is needed in order to understand the impact of age on the innate immune system and to design diets that might improve age-associated changes in innate immunity. The purpose of this study was to investigate the effects of age on phagocytosis and antibacterial activity of peripheral blood neutrophils, and on expression levels of selected mRNA specific for neutrophil migration or killing functions. Three groups of Beagle dogs were evaluated in a cross-sectional study design: puppies less than 1 year of age (n=15), adults 1-7 years of age (n=37) and senior adults over 8 years of age (n=25). Neutrophil phagocytosis and killing of Lactococcus lactis were assessed, and the relative abundance of mRNAs for myeloperoxidase (MPO), l-selectin, interleukin-8 receptor (IL-8R) and interleukin-1beta-converting enzyme (ICE) was determined. Results showed that in Beagle dogs there is a significant effect of age on percent bacterial killing by neutrophils. Average decline in phagocytic ability at 4 and 10 years of age (compared to 1 year of age) was 25% and 39%, respectively. In addition, younger dogs have significantly higher levels of mRNA for IL-8R, l-selectin and ICE. These results suggest that older dogs have depressed innate immune responses compared with younger dogs, which may contribute to increased morbidity and mortality with aging.