Influence of Housing Density and Grazing on Heat Shock Protein 27 Expression in Skeletal Muscle of Beef Cattle

Heat shock proteins (HSPs) are used as a stress biomarker in several studies as well as other stress biomarker, but the influence of different rearing environment on HSPs expression with other stress biomarker in cattle is unclear. To clear this point, two experiments were conducted to investigate the influence of rearing environment on HSP 27 in steer muscle. In experiment 1, 10 Japanese black steers were divided into 2 groups for a housing density stress experiment: a high-density (HD) group and freedom (FR) group. IgG levels and the neutrophil-to-lymphocyte (N/L) ratio in blood was analyzed as a stress marker. IgG levels and N/L ratios in the HD group were higher than those in the FR group. HSP 27 expression in the semitendinosus (ST) muscle of the HD group was higher than that of the FR group. These results suggest that HSP 27 expression may reflect the influence of the stress response with IgG levels and N/L ratios. In experiment 2, 8 Japanese Black steers were divided into 2 groups for a feeding experiment: a grazing (GR) group and concentrate-fed (CT) group. Blood IgG levels in the GR group after grazing were lower than those in the CT group. Expressions of the HSP 27 gene and its protein in the GR group were decreased in the longissimus lumborum and ST muscles compared with those in the CT group at the end of grazing. HSP 27 gene expression in the ST muscle of the GR group was lower after grazing than before grazing, but there was no significant difference in its expression in the CT group before and after grazing. The present study suggests that HSP 27 probably reflects not only differences in the rearing systems, but also the influence of the stress reaction.