PSII-14 Transcriptome response to heat stress in white blood cells of dairy calves.

Abstract The effects of stress that calves experience in their early life can impact their health and immune function. Therefore, our objective was to assess the impact of heat stress on dairy calves’ white blood cells transcriptome. Eight newborn Holstein bull calves (68.5 ± 1.37 kg of BW, aged 3.5 ± 0.5 wk, mean ± SD) gathered at the East Tennessee Ag Research and Education Center (Little River Animal and Environmental Unit, Walland, TN) were raised in individual pens following current commercial management practices. The health of calves was monitored for 2 wk before transportation to climate-controlled rooms in the Johnson Research and Teaching Unit (East Tennessee Research and Education Center, Knoxville, TN) to conduct the study. The animals had a 5-d acclimation to confinement facilities. After acclimation, calves were exposed to cyclic heat stress treatment (40°C ambient temperature from 0800 to 1900 h daily followed by 27°C, ∼12 h/d of heat stress) for 5 d. Blood samples were collected at 0, 12, and 108 h relative to treatment to conduct complete blood count and RNA extractions from white blood cells following a modified Tryzol protocol. Sequencing libraries were prepared from isolated RNA using the Takara SMART-Seq v4 3′ DE as per the manufacturer’s instructions. Final library quality and concentrations for pooling were evaluated using the Agilent Tapestation 4200 system. Libraries were sequenced on a single SP flow cell on the Illumina Novaseq 6000 with a 200-cycle v1.5 reagent kit. To control differences in tissue composition, neutrophil concentration was included as a covariate in the model. Differentially expressed genes (DEGs) across groups were called using the dream analysis workflow from the variancePartition package (adjusted P-value < 0.05) to model the repeated measures design. A total of 6 DEG were detected when comparing 0 and 12 hs (i.e., 5 downregulated and 1 upregulated). A total of 269 DEG were detected when comparing 0 h and 108 hs (i.e., 179 downregulated and 90 upregulated). The functional annotation results showed downregulation of the spliceosome and ATP-dependent chromatin remodeling KEGG pathways due to the inhibition of most of the spliceosomal RNA-related genes and several clustered histones variants. In summary, the response to heat stress was in part regulated at the post-transcriptional level by a disruption of the splicing machinery gene network. Our results suggest that translation of pre-mRNAs and ribosomal RNA transcription in white blood cells was affected by heat stress.