153 Sperm metabolomic landscape associated with bull fertility

Sub-fertility fertility in bulls decreases the efficiency and profitability of cattle production because AI allows a single bull to inseminate thousands of cows. In recent decades, there has been a general decline in fertility of bulls, even among those exhibiting normal sperm motility and morphology. Despite advances in technology and knowledge, molecular, cellular and physiological mechanisms underlying the causes of low fertility in bulls are currently unclear. Therefore, the objective of this study was to identify sperm metabolites associated with fertility in Holstein bulls. The metabolome of sperm from 10 mature bulls with high fertility (HF, n=5) and low fertility (LF, n=5) was identified by gas chromatography coupled to mass spectrometry. Bull fertility was based on the sire conception rates deviating from the average. Statistical analysis was performed by using MetaboAnalyst 3.0 (http://www.metaboanalyst.ca/). A total of 22 metabolites were detected and categorized according to their major chemical classes, including amino acids, peptides/analogues, carbohydrates/carbohydrate conjugates, fatty acids, steroids/steroid derivatives, keto acids and derivatives, carboxylic acids, and other organic and inorganic compounds. Organic acids and derivatives as well as fatty acids were the major compounds in bull spermatozoa. Seven organic acids and derivatives were detected, including benzoic acid, carbonate, carbamate dimethyl, carbamate trimethyl, lactic acid, oxalic acid, and urea. Five fatty acids were identified including oleic acid, oleanitrile, nonanoic acid, and palmitic acid. Oleic acid, phosphoric acid, phosphine, carbamate trimethyl, and glycerol were the most abundant metabolites in bull sperm, whereas benzoic acid, acetic acid, l-serine, carbamate, and 2-ketobutyric acid were the least predominant metabolites present in bull sperm. Multivariate analysis (partial least squares-discriminant analysis) of the sperm metabolome showed a clear separation between HF and LF bulls. Variable importance in projection (VIP) score demonstrated that metabolites with VIP >1.5 were gamma-aminobutyric acid (VIP=2.01), carbamate trimethyl (VIP=1.88), benzoic acid (VIP=1.86), and lactic acid (VIP=1.81). Abundance ratios of gamma-aminobutyric acid, carbamate trimethyl, benzoic acid, and lactic acid was greater in HF bulls compared with LF animals. According to univariate analysis, abundance ratios of gamma-aminobutyric acid (P=0.03) and carbamate trimethyl (P=0.047) were greater in HF than in LF bulls. Gamma-aminobutyric acid was positively correlated with carbamate trimethyl (r=0.94; P<0.0001) and benzoic acid (r=0.74; P=0.0139). Benzoic acid was positively correlated with carbamate trimethyl (r=0.75; P=0.0107) and carbamate dimethyl (r=0.68; P=0.0274). The identified metabolites can serve as potential markers to evaluate semen quality and predict bull fertility.