The energy level of the diet in Holstein cows in the first third of lactation alters the expression of immune genes in the mammary gland.

Our goal was to define the effect of the energy intake in Holstein cows' diet in the first third lactation on gene expression profile of immune system in mammary gland through RNA-seq. Twelve Holstein cows were used in the first third of lactation, arranged in four treatments or diets: (a) hypocaloric (HYPO, 85% of the net energy of lactation (NEl) requirements), (b) isocaloric (ISO, 100% of the NEl requirements, control diet), (c) hypercaloric (HYPER, 115% of the NEl requirements) and (d) isocaloric plus sunflower oil supplementation (OIL, 106% of the NEl requirements). A biopsy of mammary gland tissue was carried out after 25 days per diet, from which the RNA was extracted and sequenced using the Illumina HiSeqTM 2,500 sequencer. The analysis of reads obtained from the sequencing in the QIAGEN® CLC Genomics Workbench 10.0 bioinformatics software was performed. From 27,368 genes annotated in the reference genome, 17,429 genes expressed in the evaluated treatments were identified. Moreover, 1,743 differentially expressed genes (DEGs) were found, of which 15 DEGs were found in the ISO vs. OIL comparison, 1,196 DEGs in the ISO vs. HYPO comparison and 532 DEGs in the ISO vs. HYPER comparison. Thus, of the 1,743 DEGs, 401 correspond to genes involved in the functioning of the immune system, encompassing 23% of the total number of DEGs involved in the analysis, and 13.6% of the total number of genes involved in the functioning of the immune system. The energy intake in Holstein cows' diet has impact in the expression of immune genes CXCL13, TRDC among others, present in the regulation of immune system processes. This immune system altered might increase the somatic cells score and therefore reach some diseases. It is recommended to measure the energy intake according to the animals' energy requirements and to cover them the closest to the 100%.