# Effect of probiotics on immune cells in young Japanese Black calves responding to vaccination against bacterial respiratory diseases

## TL;DR

This study shows that giving probiotics to young calves boosts their immune response to vaccines against respiratory diseases.

## Contribution

The novel finding is that probiotics enhance immune responses in calves following vaccination.

## Key findings

- Probiotics increased lymphocyte and T cell counts in calves.
- Cytokine gene expressions (IL-4 and IL-17A) were higher in probiotic-treated calves.
- Probiotics promoted stronger immunological reactions to vaccination.

## Abstract

The vaccination against bacterial respiratory diseases in calves has been generally recognised as useful for the prevention of infections. Inducing an immunological response after vaccination is important for obtaining protection from infections. The aim of the study was to investigate the effects of probiotics on the immunological response to vaccination against bacterial respiratory diseases in young Japanese Black calves.

Twenty-four Japanese Black calves were randomly divided into two groups (12 calves for the research group and 12 calves for the control group) on the seventh day of life (dol). The research group received 30 g per day of live bacteria mix consisting of Streptococcus faecalis, Clostridium butyricum and Bacillus mesentericus until the 63rd dol. The control group did not receive the bacteria mix. All calves were vaccinated against bacterial respiratory diseases twice, at 21 and 42 dol. Blood samples were obtained from all calves at 7, 21, 42 (prior to the second vaccination), 45, 49 and 63 dol for determination of antibody titres, leukocyte numbers and cytokine genes.

Lymphocyte counts, T cell (CD3+, CD4+ and CD8+ cell) counts and relative expressions of cytokine genes (interleukin (IL)-4 and IL-17A) at 45, 49 and 63 dol were significantly higher in the research group compared than in the control group.

The addition of probiotics to young Japanese Black calves’ feed promoted an immunological reaction to vaccination against bacterial respiratory diseases.