Abstract
Heat stress has detrimental effects on livestock via diverse immune and physiological changes; heat-stressed animals are rendered susceptible to diverse diseases. However, there is relatively little information available regarding the altered immune responses of domestic animals in heat stress environments, particularly in cattle steers. This study aimed to determine the changes in the immune responses of Holstein and Jersey steers under heat stress. We assessed blood immune cells and their functions in the steers of two breeds under normal and heat stress conditions and found that immune cell proportions and functions were altered in response to different environmental conditions. Heat stress notably reduced the proportions of CD21+MHCII+ B cell populations in both breeds. We also observed breed-specific differences. Under heat stress, in Holstein steers, the expression of myeloperoxidase was reduced in the polymorphonuclear cells, whereas heat stress reduced the WC1+ γδ T cell populations in Jersey steers. Breed-specific changes were also detected based on gene expression. In response to heat stress, the expression of IL-10 and IL-17A increased in Holstein steers alone, whereas that of IL-6 increased in Jersey steers. Moreover, the mRNA expression pattern of heat shock protein genes such as Hsp70 and Hsp90 was significantly increased in only Holstein steers. Collectively, these results indicate that altered blood immunological profiles may provide a potential explanation for the enhanced susceptibility of heat-stressed steers to disease. The findings of this study provide important information that will contribute to developing new strategies to alleviate the detrimental effects of heat stress on steers.
Highlights
Seasonal changes, during the hot and humid season, can have detrimental effects on different aspects of livestock production, reproduction, metabolism, and immunity; recent trends in global warming seem exacerbate the adverse effects of environmental conditions during this season
To determine whether heat stress alters hematological parameters in steers, we analyzed the whole blood of Holstein and Jersey steers using a Vetscan® HM5 hematological analyzer, which provides a fully automated report for a 22-parameter complete blood count (CBC) from whole blood, discriminating and quantifying cell numbers based on cell size
We detected no significant differences in the white blood cells (WBC), lymphocyte, monocyte, or neutrophil counts between Holstein and Jersey steers (Fig. 1A–D)
Summary
During the hot and humid season, can have detrimental effects on different aspects of livestock production, reproduction, metabolism, and immunity; recent trends in global warming seem exacerbate the adverse effects of environmental conditions during this season. Hot and humid environmental conditions induce heat stress responses in plants and animals, which are known to have significant effects on diverse physiological processes, including those related to metabolism and immunity, and can promote the development of diseases. The findings of correlation studies have indicated that heat-stressed animals have a higher incidence of diseases, including infectious and metabolism-related diseases. The increased incidence of diseases in heat-stressed animals can be attributed to impaired immune functions. Numerous studies have revealed the detrimental effects of heat stress on the immune status of livestock. Using RNAseq technology, it was found that Holstein bull calves exposed to severe heat stress show hyperinsulinemia, along with altered expression of genes involved in immune response and immunity-related signaling pathways (Srikanth et al 2017). Administering vaccines to heat-stressed animals may not produce optimal immune responses, thereby reducing the efficacy of vaccination
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