Abstract
Boar taint is a multifactorial issue, resulting from the accumulation of androstenone and skatole in the backfat of entire male pigs. Fermentable carbohydrates in finishing feed for boars have been shown to decrease the skatole present in the carcass and the free androstenone present in the plasma at the time of slaughter. We have previously shown that the short-chain fatty acids (SCFAs) acetate, butyrate, and propionate can directly increase the metabolism of androstenone in isolated hepatocytes. However, the effect of SCFAs on skatole metabolism and gene expression is not known. Similarly, it is unclear how sex steroids influence the effect of SCFA treatments, as sex steroids affect hepatic metabolism of boar taint compounds. The objective of this trial was to examine the direct effects of SCFAs on skatole metabolism and to compare metabolism between boars and barrows to assess sex-dependent effects. Hepatocytes were isolated from 7 boars and 6 barrows (all 3-way commercial cross) using a collagenase treatment. Cells were plated and incubated with various combinations of acetate (900µM), butyrate (160µM), and propionate (300µM) overnight. Cells were then incubated with media containing skatole to assess how SCFAs affect metabolism in boars and barrows. Gene expression was assessed by qPCR and skatole metabolism and metabolite production was quantified by HPLC analysis of culture media. Skatole metabolism was compared using a One-Way ANOVA with a Dunnett’s adjustment for multiple comparisons to a control while comparisons between boars and barrows were made using a Two-Way ANOVA with a Tukey’s Adjustment for multiple comparisons Acetate had the most significant effect on skatole metabolism in boars, increasing overall skatole metabolism by 22.23±5.84% (p< 0.0001) as well as the production of HMOI (40.13±6.32%, p< 0.0001), 3MOI (21.50±3.97%, p< 0.0001), and 6-OH-3MI glucuronide (18.55±6.62%, p=0.0222) relative to the control. SCFAs did not affect skatole metabolism in barrows. Additionally, overall skatole metabolism was similar between boars and barrows, but barrows had higher metabolism in untreated control hepatocytes compared to boars. Expression of CYB5A (p< 0.0001), CYP2E1 (p=0.0014), CYP2C33 (p= 0.0242), CYP2C49 (p=0.0339), FXR (p=0.0112), AKR1C1 (p=0.001), PGC1a (p=0.0015), and UGT2A1 (p=0.0275) was increased by a combination of all 3 SCFAs in barrows. Treatment with propionate in combination with other SCFAs in hepatocytes isolated from boars significantly increased the expression of CYB5A (p=0.0003), while treatment with acetate and butyrate significantly increased CYP2E1 (p=0.0335) expression. These results demonstrate that SCFAs directly influence the metabolism of skatole in the liver by increasing the expression of key genes involved in boar taint metabolism and that these effects differ between boars and barrows, suggesting that sex steroids play an important role in mediating SCFA effects on skatole metabolism.