Combining metabolomics and genomics to elucidate physiological processes related to tail damage score in pigs

The purpose of this study was to identify important metabolitesrelated to tail damage (TDAM) score and to identify genomic regionsassociated with variation in the metabolites. We used 181 Tempo ×Topigs-20 animals divided over 2 batches balanced for gender and selectedfor positive (n = 81) or negative (n = 100) indirect genetic effect(IGE) for growth. Half of the pigs were housed in a barren environment,and the other half in an enriched environment. The tail scores were recordedat weaning and thereafter once a week (score 1 no visible taildamage, score 2 hair removed from the tail, score 3 bite marks and score4 clearly visible wound). Blood samples collected at 8, 9 and 22 weeksof age were used to determine metabolic profiles at The MetabolomicsInnovation Centre (University of Alberta). A total of 53 compoundswere quantified. Statistical analyses were performed in R version 3.5using a generalized mixed model with repeated measurements. A singlestep genome-wide association study (ssGWAS) was performed toidentify genomic regions associated with significant metabolites for tailbiting score. Preliminary results show that serum levels of glycerol andisopropanol were significantly associated with tail damage score. Animalswith TDAM 2 had greater glycerol concentration in blood whencompared with animals with TDAM 3 and 4 (P < 0.05). In addition,animals with TDAM 1 had lower isopropanol concentration when comparedwith animals with TDAM 2 and 3 (P < 0.05). GWAS identified2 candidate regions located on chromosome 6 associated with glyceroland isopropanol (at 45Mb, and at 149Mb respectively). The candidategenes identified in these regions were ZFP14, DOCK7, ANGPTL3,USP1 and KANK4. Angiopoietin like 3 is a secreted protein encoded byANGPTL3 that is involved in the regulation of lipid and glucose metabolism.This protein is present at high levels in the liver where it can bindto adipocytes to activate lipolysis, releasing free fatty acids and glycerol.These results suggest that animals with tail damage (propensity tobeing bitten) might have impaired lipolysis processes.