Low welfare impact of noise : assessment in an experimental model of mice infected by Herpes simplex-1

The breeding practices adopted and the equipment typically found in animal facilities produce sounds at frequencies within the auditory range of the mice (1 to 100 kHz), which can cause hearing and other non-hearing effects. Another aspect that could potentially affects the welfare of experimental animals would be their impaired health condition, since in addition to all the variables present in the environment, some of them are deliberately infected with pathogens. This study aimed to evaluate the possible effects of the chronic exposure of C57BL/6 and Tlr2/Tlr9(−/−) mice, uninfected and infected, with a low m.o.i. of Herpes simplex-1, at different noise levels present in the “Quiet” and “Noisy” rooms. Considering all procedures, a total of 51 male mice were used, 27 of the C57BL/6 and 24 of the Tlr2/Tlr9(−/−) strains. Physiological parameters such as weight gain, hemogram, cholesterol, glucose,corticosterone and cytokines involved in the immune response were evaluated together with the animals’ behavioral responses in Open Field and Light/Dark tests. In relation to the physiological parameters in C57BL/6, there was infection x noise interaction (P < 0.05) with greater weight gain by the infected “Quiet” group (P < 0.05) when compared to the infected “Noisy” group. In the hemogram of C57BL/6 there was infection x noise interaction (P < 0.01) in the platelets, with increase by the infected “Quiet” group when compared to the control “Quiet” and infected “Noisy” group (P < 0.05). No significant differences were found between the groups in the cholesterol, glucose and corticosterone concentrations. Regarding the production of cytokines in C57BL/6 there was infection x noise interaction (P < 0.05), with a lower production of gamma interferon in control “Quiet” group when compared to the infected “Quiet” group and to the control “Noisy” group (all P < 0.05). In behavioral tests there was no difference between the groups. Our results demonstrated that although the noise and infection influence have caused changes in some physiological and immunological parameters, they were not sufficient to promote measurable change in the stress parameters evaluated, since that corticosterone concentration and the responses of the animals from different groups in the behavioral tests were not different. This study demonstrated that the noise level found in the animal facility caused a low impact on the welfare of experimental mice