GRADUATE STUDENT LITERATURE REVIEW: Contemporary perspectives and the use of omics techniques to improve our understanding of hyperketonemia in dairy cows.

Abstract

Hyperketonemia (HYK) is a metabolic disorder defined by increased ketone concentrations, particularly β-hydroxybutyrate (BHB). It is linked to increased disease risk and reduced milk production in dairy cows due to energy deficits during early lactation. Recently, omics approaches such as genomics, transcriptomics, proteomics, and metabolomics have been used to better understand mechanisms associated to HYK. These studies have helped characterize pathways associated to energy metabolism, lipid mobilization, insulin resistance, and immune response, with associated genes identified in several genome regions, including Bos taurus autosome 6. Omics studies have identified biomarkers, such as methanol, C16, and phosphatidylcholine acyl-alkyl C30:2, which have been associated with or predictive of HYK, with elevated levels detectable up to 4 weeks before calving. Limitations of omics studies include the small sample sizes of controlled study designs, standardizing sampling timelines, and translating the large amounts of data generated into practical applications. While global changes in other body fluids have been well-characterized, research focused on the role of the rumen fluid metagenome and metabolome is much more limited. Changes in rumen metabolites and microbes are important to consider in relation to HYK, as associated shifts in dry matter intake and diet can alter rumen function and subsequent nutrient metabolism and absorption. Shifts in microbial communities, such as Ruminococcaceae, and altered metabolite profiles, including increased butyrate in HYK cows, may offer insights to guide on farm decisions, such as dietary interventions or feed additive use. Overall, although HYK in dairy cows is a topic that has been extensively studied, improved understanding of its etiology and advances in 'big data' technologies have created continued opportunities to further understand HYK and the factors associated with it. Thus, the focus of this review is to provide an overview of omics methods and how they have been used to further describe HYK as well as explore new associations of omics methods and rumen parameters with HYK.