In Utero Heat Stress and Genomic Selection for Heat Tolerance Alter Seminal Plasma Metabolite Profiles Associated with Semen Quality

In utero heat stress (IUHS) decreases sperm production in boars by ∼7 billion cells per ejaculate, yielding ∼600 fewer artificial insemination doses per lifetime. Recent studies link seminal plasma metabolite concentrations with divergent semen quality, but the seminal plasma metabolome of IUHS boars has not been studied. The primary objective was to quantify short-chain fatty acids (SCFA), fatty acid methyl esters (FAME), and phenolics in seminal plasma of IUHS and in utero thermoneutral (IUTN) boars and then determine if concentrations correlate with sperm quality metrics. Further, boars were derived from parents genomically selected for more heat-tolerance (TOL) or heat-sensitivity (SEN) as a potential mitigation strategy. Dams were housed in either cyclic heat stress (26–36 °F) or thermoneutral (17–20 °F) conditions from 6–70 d of gestation. Resulting boars were classified as: IUHS+SEN, IUHS+TOL, IUTN+SEN, or IUTN+TOL (n = 6–9 per treatment). Semen was collected weekly for 10 weeks and subjected to computer-assisted sperm analysis. Seminal plasma was isolated from ejaculates, pooled by boar, and analyzed via targeted mass spectrometry for SCFA, FAME, and phenolics. The MIXED procedure of SAS was used to assess concentrations with boar as the experimental unit and treatment as the fixed effect. The CORR procedure was utilized to evaluate possible associations between sperm quality metrics and metabolite concentrations. Regarding SCFA, formate concentrations were greater in IUTN+TOL versus IUHS+TOL or IUTN+SEN samples (P < 0.05). Additionally, IUHS+SEN boars had a greater concentration of formate in seminal plasma versus IUHS+TOL boars (P = 0.05). Butyrate concentrations were elevated in IUHS+TOL seminal plasma compared with all other treatments (P < 0.05). Numerous sperm quality parameters were moderately correlated with butyrate, including progressive (r=-0.66; P < 0.01) and total (r=-0.65; P < 0.01) motility, and normal morphology (r=-0.67; P < 0.01). For phenolics, IUHS+TOL seminal plasma had a greater concentration of p-coumaric acid than all other treatments (P < 0.05). Interestingly, FAME analysis revealed that lauric and myristic acid were greater in IUHS+SEN and IUTN+SEN boars compared with IUHS+TOL (P < 0.05). Arachidic, behenic, and tetracosanoic acids were elevated in IUTN+SEN samples compared with IUHS+TOL and IUTN+TOL (P < 0.05). Oleic acid was increased in IUTN+SEN compared with IUHS+TOL boars (P < 0.01). Stearic acid tended (P = 0.10) to be greater in IUTN+SEN versus IUHS+TOL boars (P = 0.02). Sperm concentration was moderately or strongly correlated with lauric (r = 0.43; P = 0.02), myristic (r = 0.74; P < 0.01), stearic (r = 0.72; P < 0.01), oleic (r = 0.73; P < 0.01), arachidic (r = 0.56; P < 0.01), behenic (r = 0.56; P < 0.01), and tetracosanoic (r = 0.52; P < 0.01) acids. Stearic acid also correlated with total sperm number (r = 0.40; P = 0.02) and artificial insemination dose number (r = 0.40; P = 0.02). Overall, IUHS and genomic selection for heat tolerance alter the porcine seminal plasma metabolome. Several alterations suggest less favorable semen quality in IUHS-exposed boars, which were not ameliorated by thermotolerant genotype. Additionally, IUTN+SEN boars had profiles associated with greater sperm concentration and motility, suggesting enhanced reproductive potential.