The Association Between Hematological Profiles and Whole-Blood Transcriptome Genes Identified Using Quantitative...

Feed is the single greatest cost for cattle producers. Improvements to feed efficiency, or how animals convert feed to body weight gain, will ultimately improve producer profits. The objective of this study was to determine whether the expression of genes in the transcriptome of whole blood from heifers (n = 61) on a forage ration was related to the quantitative phenotypes for average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed (G:F). Total RNA was isolated from whole blood collected mid-study on day 42 on feed and was used for hematologic analysis and RNA-sequencing. Lymphocyte (LYM) count was negatively associated with ADG, and mean corpuscular hemoglobin concentration (MCHC) was positively associated (p < 0.05). Red blood cell (RBC) count was negatively associated with ADFI. While MCHC was positively associated with G:F, white blood cell (WBC), LYM, and basophil (BAS) counts were negatively associated with G:F (p ≤ 0.05). The model used to identify differentially expressed genes (DEG) for ADFI, ADG, and G:F included sire, breed, pen, age, and proportions of blood cell types. No genes were differentially expressed for ADFI. Three genes were identified as differentially expressed for ADG, and 17 were identified for G:F. Three of the differentially expressed genes for G:F and ADG (PLOD1, FAH, and COL1A2) had been previously associated with feed efficiency in livestock and may be useful for further validation in other populations of cattle. The negative associations between WBC and LYM and ADG and G:F may be expected since the production of WBC is an energetic process that may reduce body weight gain and efficiency. The associations between RBC hematological parameters suggest that there may be benefit for animals with higher levels of hemoglobin per RBC by improving oxygen-carrying capacity.