Abstract
Simple SummaryRecently, it has become apparent that the microbiome is essential to health and affects practically every aspect of physiology. The rumen contains highly dense and diverse microbial communities, which can impact health through their composition, diversity, and assembly. Nevertheless, the diversity and function of rumen microbes have not been fully described. Therefore, this study aims to identify differences in the functional attributes and metabolites of rumen microbiota to heat stress by metagenomics and metabolomics analyses. We observed differences in biological changes, as well as changes in rumen metabolites and metabolic pathways depending on the breed of cow. In addition, significant changes in rumen bacterial taxa and functional gene abundance were observed. Overall, the findings of this study improve our understanding of heat-vulnerable ruminal bacteria and related genes.The microbial community within the rumen can be changed and shaped by heat stress. Accumulating data have suggested that different breeds of dairy cows have differential heat stress resistance; however, the underlying mechanism by which nonanimal factors contribute to heat stress are yet to be understood. This study is designed to determine changes in the rumen microbiome of Holstein and Jersey cows to normal and heat stress conditions. Under heat stress conditions, Holstein cows had a significantly higher respiration rate than Jersey cows. Heat stress increased the rectal temperature of Holstein but not Jersey cows. In the Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis, Jersey cows had a significantly higher proportion of genes associated with energy metabolism in the normal condition than that with other treatments. Linear discriminant analysis effect size (LEfSe) results identified six taxa as distinguishing taxa between normal and heat stress conditions in Holstein cows; in Jersey cows, 29 such taxa were identified. Changes in the rumen bacterial taxa were more sensitive to heat stress in Jersey cows than in Holstein cows, suggesting that the rumen mechanism is different in both breeds in adapting to heat stress. Collectively, distinct changes in rumen bacterial taxa and functional gene abundance in Jersey cows may be associated with better adaptation ability to heat stress.
Highlights
With the continual increase in global greenhouse gas emissions, climate change has become a major global issue for agricultural land and livestock animal production
The climate in West Asia has been changing from a humid subtropical climate to a tropical climate [2]. This climate change will result in a reduction in the productivity of livestock animals; the development of strategies for rearing livestock animals in ambient temperature is needed to overcome the negative impact of climate change
In Holstein cows, the composition of the distinct microbial community suggests that microbiome changes with the enrichment of Fibrobacteres under heat stress may be a source of heat generation
Summary
With the continual increase in global greenhouse gas emissions, climate change has become a major global issue for agricultural land and livestock animal production. The climate in West Asia has been changing from a humid subtropical climate to a tropical climate [2]. This climate change will result in a reduction in the productivity of livestock animals; the development of strategies for rearing livestock animals in ambient temperature is needed to overcome the negative impact of climate change. Temperature-sensitive neurons are located throughout the animal body; these neurons send information to the hypothalamus, which invokes numerous physiological, anatomical, and behavioral changes in an attempt to maintain heat balance [4,5,6]. Changes in the ambient temperature lead to increased management costs and reduced profits for the animal industry [12]
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