167 Plasma Metabolomics at Weaning and 30 Days Prior to Ai in Beef Heifers with Varying Reproductive Potential
Authors: Holliman Anna , Banerjee Priyanka , Dyce Paul W W 
Published: November 2023

Abstract
Cattle are an economically important species, and subfertility is one of the reasons for economical loss for producers. Despite the use of phenotypic measures in selection, such as body condition score, reproductive tract score and age, a subset of heifers will fail to conceive by the end of a defined breeding season. Therefore, diagnostic biomarkers are desired that can successfully discriminate fertile and subfertile beef heifers. Metabolites are small molecules present in biofluids and tissues, relating to metabolic processes of cells and organs. The metabolome, the global population of small molecules, is highly impacted by environmental interactions. Therefore, for this study, metabolomic profiles were generated on beef heifers with varying reproductive potential. Angus-Simmental heifers were subjected to estrus synchronization (Select Synch+CIDR protocol), estrus detection and artificial insemination, and natural breeding service protocols. Blood samples were collected from all the heifers at the time of weaning and from a subset of the same heifers at 30 days before AI. Depending on presence or absence of conceptus after 75 days of AI, the heifers were categorized as fertile (pregnant to AI) or subfertile (not pregnant) groups. Plasma metabolome profiles were generated for 12 heifers (6 in each group) using GC-TOF-MS from the blood plasma collected at weaning and from 7 heifers (3 fertile and 4 subfertile) at 30 days prior to AI. Metabolomic profiles were analyzed using MetaboAnalyst v5.0 utilizing Students t-test, principal component, and partial least squares discriminate analyses. Nine metabolites including arabitol, lyxitol, lactic acid, and nicotinamide were significant (P ≤ 0.05) between subfertile and fertile heifers at weaning. Four metabolites including tryptophan and palmitoleic acid were significant between subfertile and fertile heifers at 30 days before to AI. ROC-AUC curves identified arabitol, tryptophan, and palmitoleic acid with AUC values of 1 (P ≤ 0.05) within their respective timepoints. ROC-AUC curves for lyxitol, lactic acid, and nicotinamide had AUC values of 0.778, 0.917, and 0.806, respectively. These metabolites interact with pathways like pentose and glucuronate interconversions (arabitol and lyxitol), fatty acid degradation (palmitoleic acid), pyruvate metabolism and gluconeogenesis/glycogenesis (lactic acid), aminoacyl-tRNA biosynthesis and tryptophan metabolism (tryptophan), and nicotinate and nicotinamide metabolism (nicotinamide). Additionally, individual activities of these metabolites point to interactions with increased stress at weaning, immune cell efficiency, and energy metabolism. This opens up avenues of testing metabolite levels that could potentially identify heifers in periods of subfertility at multiple time points, reducing the resources and time spent on them for estrus synchronization or AI breeding. However, further targeted study is required to fully elucidate the discriminatory potential of these metabolites.