Abstract
Korean peninsula weather is rapidly becoming subtropical due to global warming. In summer 2018, South Korea experienced the highest temperatures since the meteorological observations recorded in 1907. Heat stress has a negative effect on Holstein cows, the most popular breed of dairy cattle in South Korea, which is susceptible to heat. To examine physiological changes in dairy cows under heat stress conditions, we analyzed the profiles circulating microRNAs isolated from whole blood samples collected under heat stress and non-heat stress conditions using small RNA sequencing. We compared the expression profiles in lactating cows under heat stress and non-heat stress conditions to understand the regulation of biological processes in heat-stressed cows. Moreover, we measured several heat stress indicators, such as rectal temperature, milk yield, and average daily gain. All these assessments showed that pregnant cows were more susceptible to heat stress than non-pregnant cows. In addition, we found the differential expression of 11 miRNAs (bta-miR-19a, bta-miR-19b, bta-miR-30a-5p, and several from the bta-miR-2284 family) in both pregnant and non-pregnant cows under heat stress conditions. In target gene prediction and gene set enrichment analysis, these miRNAs were found to be associated with the cytoskeleton, cell junction, vasculogenesis, cell proliferation, ATP synthesis, oxidative stress, and immune responses involved in heat response. These miRNAs can be used as potential biomarkers for heat stress.
Highlights
Following global warming, including the northward expansion of the subtropical climate zone, South Korea, located at the northern hemisphere of East Asia, is susceptible to the impact of climate change [1,2,3]
We observed that minimum temperaturehumidity index (THI) exceeded 72 from the first week of July and even reached over 80, and moderate/severe heat stress (HS) conditions (THI > 78) lasted for over one month
Both maximum and minimum THI peaked around mid-August, and gradually declined; mild to moderate HS (THI 72–78) was detected until the end of September
Summary
Following global warming, including the northward expansion of the subtropical climate zone, South Korea, located at the northern hemisphere of East Asia, is susceptible to the impact of climate change [1,2,3]. The average increase in temperature in South Korea was 1.7 ̊C, while global temperature increased by 0.7 ̊C from 1912 to 2008 [2, 4]. In summer 2018, South Korea experienced extreme hot temperatures since the meteorological observations recorded in 1907. Heat stress (HS) has a negative influence on livestock. Effect of heat stress on miRNA expression in lactating Holstein cows
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