Effects of dietary selenized glucose on intestinal microbiota and tryptophan metabolism in rats: Assessing skatole reduction potential

3-Methylindole (Skatole), a degradation product of tryptophan produced by intestinal microbial activity, significantly contributes to odor nuisance. Its adverse effects on animal welfare, human health, and environmental pollution have been noted. However, it is still unclear whether the intestinal microbiota mediates the impact of selenium (Se) on skatole production and what the underlying mechanisms remain elusive. A selenized glucose (SeGlu) derivative is a novel organic selenium compound. In this study, a diverse range of dietary SeGlu-treated levels, including SeGlu-deficient (CK), SeGlu-adequate (0.15 mg Se per L), and SeGlu-supranutritional (0.4 mg Se per L) conditions, were used to investigate the complex interaction of SeGlu on intestinal microbiome and serum metabolome changes in male Sprague-Dawley (SD) rats. The study showed that SeGlu supplementation enhanced the antioxidant ability in rats, significantly manifested in the increases of the activity of catalase (CAT) and glutathione peroxidase (GSH-Px), while no change in the level of malonaldehyde (MDA). Metagenomic sequencing analysis verified that the SeGlu treatment group significantly increased the abundance of beneficial microorganisms such as Clostridium, Ruminococcus, Faecalibacterium, Lactobacillus, and Alloprevotella while reducing the abundance of opportunistic pathogens such as Bacteroides and Alistipes significantly. Further metabolomic analysis revealed phenylalanine, tyrosine, and tryptophan biosynthesis changes in the SeGlu treatment group. Notably, the biosynthesis of indole, a critical pathway, was affected by SeGlu treatment, with several crucial enzymes implicated. Correlation analysis demonstrated strong associations between specific bacterial species - Treponema, Bacteroides, and Ruminococcus, and changes in indole and derivative concentrations. Moreover, the efficacy of SeGlu-treated fecal microbiota was confirmed through fecal microbiota transplantation, leading to a decrease in the concentration of skatole in rats. Collectively, the analysis of microbiota and metabolome response to diverse SeGlu levels suggests that SeGlu is a promising dietary additive in modulating intestinal microbiota and reducing odor nuisance in the livestock and poultry industry.

Mulberry leaf supplementation inhibits skatole deposition by regulating gut microbiota and upregulating liver cytochrome P450 1A1 expression in finishing pigs

Skatole, a strong fecal odor substance, is generated through microbial degradation of tryptophan in the animal hindgut. It easily accumulates in adipose tissue and affects meat quality. In this study, the effect of mulberry leaf supplementation on skatole in finishing pigs was studied. In a 35-day trial, 20 finishing pigs (barrows and gilts) were fed with a basal diet or basal diet with 6% mulberry leaves. Growth performance of the pigs (n = 10) was automatically recorded by a performance-testing feeder system and 8 pigs in each treatment were slaughtered and sampled for the remaining tests. Skatole and short-chain fatty acids were detected using HPLC and gas chromatography, respectively. Fecal microbiota were analyzed using 16S rRNA gene sequencing. The metabolomics analysis of feces and serum was performed with UHPLC-MS/MS. The major cytochrome P450 (CYP) enzymes that catalyze skatole degradation in the liver were tested by using RT-PCR and Western blot. Effects of major bioactive compounds in mulberry leaves on the CYP genes were verified in the hepatic cell line HepG2 in an in vitro test (n = 3). In finishing pigs, mulberry leaf supplementation had no significant effect on the average daily gain, average daily feed intake, and feed conversion ratio (P > 0.05), but reduced skatole levels in feces, serum, and backfat (P < 0.05), and increased acetic acid levels in feces (P = 0.027). Mulberry leaf supplementation decreased the relative abundance of the skatole-producing bacteria Megasphaera and Olsenella (P < 0.05). Indole-3-acetic acid, the intermediate that is essential for skatole production, was significantly reduced in feces by mulberry leaf supplementation (P < 0.05) and was positively correlated with skatole content in feces (P = 0.004). In pigs treated with mulberry leaves, liver CYP1A1 expression was increased (P < 0.05) and was negatively correlated with skatole content in backfat (P = 0.045). The in vitro test demonstrated that mulberry leaf polyphenols and polysaccharides could directly stimulate CYP1A1 expression in hepatic cells. These findings suggest that mulberry leaf supplementation reduces skatole production and deposition in finishing pigs by regulating the gut microbiota and promoting skatole degradation in liver.

The effects of different immunocastration protocols on meat quality traits and boar taint compounds in male Bísaro pigs

Immunocastration can be an alternative to surgical castration in Bísaro pigs when there is a need to keep animals on the farm until at least 8 months old. As an autochthonous breed, some particularities must be addressed when doing immunocastration, for which 3 different protocols were tested and two control groups were made with surgically castrated males (SC) and boars (Bo). Two protocols were made in prepubertal pigs, with two (E2) and three inoculations (L3) in the first cycle, and another in adults (A2) with only two inoculations. Physicochemical parameters and boar taint compounds quantification and sensory analysis of the meat from the studied pigs were assessed. Immunocastration provided intermediate values between surgically castrated pigs and entire males, with low levels of boar taint compounds. The L3 group provided closer results to SC, which was also corroborated by the sensory analysis. Although the other two protocols had no significant differences with Bo, there was a positive tendency towards them. As is, the L3 protocol was promising as a good alternative to surgical castration, maintaining the characteristic attributes of the Bísaro pig meat.

Change in fat skatole and indole content in lambs switched from a concentrate-based diet indoors to alfalfa grazing for various durations before slaughter

Meat from lambs fattened on alfalfa is at risk of excessive pastoral flavours due to high levels of in-fat volatile indolic compounds (especially, skatole). Skatole has also been identified as a potential marker of interest for authenticating pasture-fed lamb meat. Here, we investigated the change in skatole and indole concentrations in kidney fat from lambs switched from an indoor-fed concentrate based diet to outdoor alfalfa grazing for various durations (0, 21, 42, 63 days) before slaughter. The study used a total of 219 lambs over 3 consecutive years. Kidney-fat skatole and indole concentrations increased from as early as 21 days on alfalfa, and then reached a plateau. Similarly, the proportion of lambs that had a kidney fat-skatole concentration above 0.15 μg/g liquid fat, a value that has been established as a sensory rejection threshold for pork, increased significantly from as early as 21 days on alfalfa and then reached a plateau. This value was reached or exceeded in a significant proportion of lambs fattened on alfalfa pastures (45.1%). However, skatole was not detected in kidney fat from 20 out of 164 alfalfa-fattened lambs (i.e., 12.2%) but was detected in 15 out of 55 concentrate-fed lambs (i.e., 27.3%). We thus conclude that while skatole content in kidney fat can inform on dietary changes made shortly before slaughter, it does not have the discrimination power needed to reliably authenticate pasture-fed lamb meat, let alone duration of finishing on pasture.

Microbiome-metabolomics analysis reveals abatement effects of itaconic acid on odorous compound production in Arbor Acre broilers

BACKGROUND

Public complaints concerning odor emissions from intensive livestock and poultry farms continue to grow, as nauseous odorous compounds have adverse impacts on the environment and human health. Itaconic acid is a metabolite from the citric acid cycle of the host and shows volatile odor-reducing effects during animal production operations. However, the specific role of itaconic acid in decreasing intestinal odorous compound production remains unclear. A total of 360 one-day-old chicks were randomly divided into 6 treatment groups: control group (basal diet) and itaconic acid groups (basal diet + 2, 4, 6, 8 and 10 g/kg itaconic acid). The feeding experiment lasted for 42 d.

RESULTS

Dietary itaconic acid supplementation linearly and quadratically decreased (P < 0.05) the cecal concentrations of indole and skatole but did not affect (P > 0.05) those of lactic, acetic, propionic and butyric acids. The cecal microbial shift was significant in response to 6 g/kg itaconic acid supplementation, in that the abundances of Firmicutes, Ruminococcus and Clostridium were increased (P < 0.05), while those of Bacteroidetes, Escherichia-Shigella and Bacteroides were decreased (P < 0.05), indicative of increased microbial richness and diversity. Furthermore, a total of 35 significantly (P < 0.05) modified metabolites were obtained by metabolomic analysis. Itaconic acid decreased (P < 0.05) the levels of nicotinic acid, nicotinamide, glucose-6-phosphate, fumatic acid and malic acid and increased (P < 0.05) 5-methoxytroptomine, dodecanoic acid and stearic acid, which are connected with the glycolytic pathway, citrate acid cycle and tryptophan metabolism. Correlation analysis indicated significant correlations between the altered cecal microbiota and metabolites; Firmicutes, Ruminococcus and Clostridium were shown to be negatively correlated with indole and skatole production, while Bacteroidetes, Escherichia-Shigella and Bacteroides were positively correlated with indole and skatole production.

CONCLUSIONS

Itaconic acid decreased cecal indole and skatole levels and altered the microbiome and metabolome in favor of odorous compound reduction. These findings provide new insight into the role of itaconic acid and expand its application potential in broilers.

Unraveling the skatole biodegradation process in an enrichment consortium using integrated omics and culture-dependent strategies

3-Methylindole (skatole) is regarded as one of the most offensive compounds in odor emission. Biodegradation is feasible for skatole removal but the functional species and genes responsible for skatole degradation remain enigmatic. In this study, an efficient aerobic skatole-degrading consortium was obtained. Rhodococcus and Pseudomonas were identified as the two major and active populations by integrated metagenomic and metatranscriptomic analyses. Bioinformatic analyses indicated that the skatole downstream degradation was mainly via the catechol pathway, and upstream degradation was likely catalyzed by the aromatic ring-hydroxylating oxygenase and flavin monooxygenase. Genome binning and gene analyses indicated that Pseudomonas, Pseudoclavibacter, and Raineyella should cooperate with Rhodococcus for the skatole degradation process. Moreover, a pure strain Rhodococcus sp. DMU1 was successfully obtained which could utilize skatole as the sole carbon source. Complete genome sequencing showed that strain DMU1 was the predominant population in the consortium. Further crude enzyme and RT-qPCR assays indicated that strain DMU1 degraded skatole through the catechol ortho-cleavage pathway. Collectively, our results suggested that synergistic degradation of skatole in the consortium should be performed by diverse bacteria with Rhodococcus as the primary degrader, and the degradation mainly proceeded via the catechol pathway.

Increasing sustainability in pork production by using high inclusion levels of co-products DDGS, wheat middling and canola meal doesn't affect pig growth performance and meat quality but reduce boar taint

Objective

the present study is to examine the effect of high inclusion of co-products in pig diets (referred to as an alternative diet) during the finishing stage on pig growth performance, meat quality and boar taint compounds.

Methods

Growing pigs were fed an alternative diet made with distillers dried grains with solubles (DDGS, 25%), canola meal (CM, 20%), and wheat middling (WM, 15%) or a control diet based on barley and soybean meal (SBM) to investigate the impact of co-products on pig performance and meat quality. Sixteen female and sixteen entire male Duroc × (Large White × Landrace) pigs (22.6 ± 2.07 kg, body weight ± SE) were equally allocated to the diets.

Result

Pigs fed the alternative diet had a lower feed intake; however, growth rate and feed conversion efficiency were unaffected by diet. A diet by sex interaction was found for gain:feed whereby males fed the alternative diet had the best feed conversion (P < 0.01). Pork from pigs fed the alternative diet had lower a* and Chroma and protein % (P < 0.05), while other meat quality characteristics were unaffected. The alternative diet reduced backfat skatole levels (P < 0.001).

Conclusion

A diet containing a high inclusion levels of co-products can be fed to pigs during the finishing stage without detrimental effects on pig performance or meat quality and with the potential to enhance pork flavour. This finding suggests a solution to increase the sustainable development of pig production.

Transcriptomic profiling reveals the molecular responses of Rhodococcus aetherivorans DMU1 to skatole stress

Skatole is a typical malodor compound in animal wastes. Several skatole-degrading bacterial strains have been obtained, whereas the molecular response of strains to skatole stress has not been well elucidated. Herein, the skatole degradation by a Gram-positive strain Rhodococcus aetherivorans DMU1 was investigated. Strain DMU1 showed high efficiency in skatole degradation under the conditions of 25-40 °C and pH 7.0-10.0. It could utilize various aromatics, including cresols, phenol, and methylindoles, as the sole carbon source for growth, implying its potential in the bioremediation application of animal wastes. Transcriptomic sequencing revealed that 328 genes were up-regulated and 640 genes were down-regulated in strain DMU1 when grown in the skatole-containing medium. Skatole increased the gene expression levels of antioxidant defense systems and heat shock proteins. The expression of ribosome-related genes was significantly inhibited which implied the growth inhibition of skatole. A rich set of oxidoreductases were changed, and a novel gene cluster containing the flavoprotein monooxygenase and ring-hydroxylating oxygenase genes was highly up-regulated, which was probably involved in skatole upstream degradation. The upregulation pattern of this gene cluster was further verified by qRT-PCR assay. Furthermore, skatole should be mainly degraded via the catechol ortho-cleavage pathway with cat25170 as the functional gene. The gene cat25170 was cloned and expressed in E. coli BL21(DE3). Pure enzyme assays showed that Cat25170 could catalyze catechol with Km 9.96 μmol/L and kcat 12.36 s-1.

Skatole: A thin red line between its benefits and toxicity

Skatole (3-methylindole) is a heterocyclic compound naturally found in the feces of vertebrates and is produced by certain flowers. Skatole has been used in specific products of the perfume industry or as a flavor additive in ice cream. Additionally, skatole is formed by tryptophan pyrolysis of tobacco and has been demonstrated to be a mutagen. Skatole-induced pulmonotoxicity was reliably described in ruminants and rodents, but no studies have been conducted in humans. Initially, we provide basic knowledge and a historical overview of skatole. Then, skatole bacterial formation in the intestine is described, and the importance of the microbiome during this process is evaluated. Increased skatole concentrations could serve as a marker for intestinal disease development. Therefore, the human molecular targets of skatole that may have significant effects on various processes in the human body are described. Ultimately, we suggest a link between skatole intestinal formation in humans and skatole-induced pulmonotoxicity, which should be explored further in the future.

Soybean oligosaccharides attenuate odour compounds in excreta by modulating the caecal microbiota in broilers

Abatement of odour emissions in poultry production is important to ensure the quality and safety in the poultry industry as well as for the benefit of the environment. This study was conducted to compare the effects of supplementation with different amounts of dietary soybean oligosaccharides (SBO) and chlortetracycline (CHL) on the major odour-causing compounds in the excreta and on the caecal microbiota in broiler chickens. One-day-old broiler chickens were subjected to a 42-day experiment involving 6 treatments with 6 replicates per treatment (10 birds/cage). The treatments were as follows: negative control (NC; basal diet), positive control (PC; basal diet supplemented with CHL) and basal diet supplemented with 0.5, 2.0, 3.5 and 5.0 g/kg SBO (0.5SBO, 2.0SBO, 3.5SBO and 5.0SBO, respectively). Fresh excreta were sampled for the analysis of odour compounds by HPLC. Caecum content was collected for the caecal microbiota analysis through 16S rRNA sequencing. Results showed that on day 42, the excreta indole concentration in the broilers fed with 2.0SBO, 3.5SBO and 5.0SBO and PC was significantly decreased (P < 0.01) compared with that in the NC-fed broilers. The excreta skatole concentration (P < 0.001) and pH (P < 0.05) were also decreased by SBO and CHL, and they were lowest in birds fed with 3.5SBO. The formate concentrations in birds fed with 3.5SBO and 5.0SBO were higher than those in birds fed with the other diets (P < 0.001). Similarly, acetate concentration (P = 0.003) was increased in birds fed with 3.5SBO. Deep sequencing of 16S rRNA revealed that the composition of the caecal microbial digesta was slightly or significantly changed by the SBO or by the CHL supplementation, respectively. The SBO supplementation decreased the abundance of Bacteroides, Bilophilaand Escherichia, which were associated with the skatole and indole concentrations in the excreta. By contrast, the CHL supplementation demonstrated a strong tendency to enrich Ruminococcus and to reduce the abundance of Rikenella. These results indicated that supplementation with dietary SBO is beneficial in attenuating the concentration of odour-causing compounds and that it modulates the composition of caecal microbiota in broiler chickens.

High throughput method for quantifying androstenone and skatole in adipose tissue from uncastrated male pigs by laser diode thermal desorption-tandem mass spectrometry

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Boar taint is mainly caused by the compounds, skatole and androstenone.

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Analysis for at-line industrial measurement of boar taint in pigs.

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High throughput quantitative analysis of skatole and androstenone.

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Low cost, robust and selective analytical results.

The study aims at developing a rapid and robust mass spectrometric method capable of measuring the malodorous boar taint compounds androstenone and skatole in fat samples from male pig carcasses. The developed method is suited for use in commercial abattoirs as an at-line method to detect the presence of these compounds in carcasses or as a high-speed analysis in laboratories with high sample turnover. The chemical assay is based on salt-assisted liquid-liquid extraction and direct measurement with Laser Diode Thermal Desorption-Tandem Mass Spectrometry (LDTD-MS/MS). When fully automated as an at-line method, a single LDTD-MS/MS system will have a measuring capacity of >420 male pig carcasses per hour. The limit of quantification (LOQ) is 0.05 µg/g and 0.10 µg/g for skatole and androstenone, respectively, which is well below the expected sorting thresholds. The reproducibility of the method (%RSD) meets the industry requirement for an RSD of below 10%.

Recent genetic advances on boar taint reduction as an alternative to castration: a review

Boar taint is an unpleasant odor in male pig meat, mainly caused by androstenone, skatole, and indole, which are deposited in the fat tissue. Piglet castration is the most common practice to prevent boar taint. However, castration is likely to be banished in a few years due to animal welfare concerns. Alternatives to castration, such as genetic selection, have been assessed. Androstenone and skatole have moderate to high heritability, which makes it feasible to select against these compounds. This review presents the latest results obtained on genetic selection against boar taint, on correlation with other traits, on differences in breeds, and on candidate genes related to boar taint. QTLs for androstenone and skatole have been reported mainly on chromosomes 6, 7, and 14. These chromosomes were reported to contain genes responsible for synthesis and degradation of androstenone and skatole. A myriad of work has been done to find markers or genes that can be used to select animals with lower boar taint. The selection against boar taint could decrease performance of some reproduction traits. However, a favorable response on production traits has been observed by selecting against boar taint. Selection results have shown that it is possible to reduce boar taint in few generations. In addition, modifications in diet and environment conditions could be associated with genetic selection to reduce boar taint. Nevertheless, costs to measure and select against boar taint should be rewarded with incentives from the market; otherwise, it would be difficult to implement genetic selection.

Effects of dietary stachyose levels on caecal skatole concentration, hepatic cytochrome P450 mRNA expressions and enzymatic activities in broilers

Effects of dietary supplemental stachyose on caecal skatole concentration, hepatic cytochrome P450 (CYP450, CYP) mRNA expressions and enzymatic activities in broilers were evaluated. Arbor Acre commercial mixed male and female chicks were assigned randomly into six treatments. The positive control (PC) diet was based on maize-soyabean meal, and the negative control (NC) diet was based on maize-non-soyabean meal. The NC diet was then supplemented with 4, 5, 6 and 7 g/kg stachyose to create experimental diets, named S-4, S-5, S-6 and S-7, respectively. Each diet was fed to six replicates of ten birds from days 1 to 49. On day 49, the caecal skatole concentrations in the PC, S-4, S-5, S-6 and S-7 groups were lower than those in the NC group by 42·28, 23·68, 46·09, 15·31 and 45·14 % (P < 0·01), respectively. The lowest pH value was observed in the S-5 group (P < 0·05). The stachyose-fed groups of broilers had higher caecal acetate and propionate levels compared with control groups, and propionate levels in the S-6 and S-7 groups were higher than those in the S-4 and S-5 groups (P < 0·001). The highest CYP3A4 expression was found in the S-7 group (P < 0·05), but this was not different from PC, S-4, S-5 and S-6 treatments. There was no significant difference in CYP450 (1A2, 2D6 and 3A4) enzymatic activities among the groups (P > 0·05). In conclusion, caecal skatole levels can be influenced by dietary stachyose levels, and 5 g/kg of stachyose in the diet was suggested.

Bacterial and fungal community compositions and structures of a skatole-degrading culture enriched from pig slurry

In this study, the aerobic activated sludge for skatole removal was enriched from pig slurry in three parallel sequencing batch reactors. The sludge system exhibited a satisfactory performance for skatole removal during the 40 days operation. High-throughput sequencing results showed that the α-diversity remained unchanged before and after the operation process. However, the structures of bacterial and fungal communities notably shifted. Particularly, Arthrobacter increased to be the major bacterial genus from 2.15 ± 0.76% (day 0) to 23.80 ± 24.36% (day 40), and Fusicolla became the major fungal genus from 1.20 ± 0.48% (day 0) to 37.17 ± 7.47% (day 40). These results indicated that Arthrobacter and Fusicolla might participate in skatole removal in sludge systems, though both genera were not reported to be able to degrade skatole. This is the first study describing skatole-degrading bacterial and fungal communities in the enrichment from pig slurry to the best of our knowledge, providing important guidance for skatole control and bioremediation.

Removal of malodorant skatole by two enriched microbial consortia: Performance, dynamic, function prediction and bacteria isolation

Malodor emission has become one of the major challenges in animal husbandry. Skatole, one of the most offensive odorous compounds, can cause several diseases to organisms and is resistant to biodegradation. However, the microbial community information for skatole degradation has yet to be reported. In this study, the aerobic sequencing batch reactors with two different inocula were constructed. Both Group N (sample from cattle house) and Group E (sample from goose house) could efficiently degrade skatole after 70 days operation under conditions of pH 7.0-9.0 and temperature 20-40 °C. High-throughput sequencing results showed that the α-diversity in Group N was higher than that in Group E, while neither of them changed during the whole operation process. Bacterial community structures in both groups shifted. Generally, Lactococcus, Pseudomonas and Flavobacterium remarkably reduced, while Arthrobacter became the dominant population. Function prediction results indicated that the xenobiotics biodegradation and metabolism category was significantly up-regulated in Group E but remained unchanged in Group N. On the other hand, culture-dependent technique was applied and ten bacteria were obtained from the sludges. Two strains belonged to Rhodococcus, a minor genus in the communities, were firstly proven to harbor excellent skatole-degrading capacity. This study proved that skatole could be effectively removed by activated sludges, and the non-core bacteria Rhodococcus would be functionally important in the degradation process. These findings provide new insights into our understanding of skatole biotransformation process, and offer valuable bacterial resources for bioremediation application.

Validation by collaborative trial of a method for the determination by GC-MS and LC-MS/MS of boar taint marker compounds in pork tissue

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Simultaneous determination of indole, skatole, and androstenone in pork tissue.

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Sensorial thresholds are within working ranges of the method.

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Choice of sample measurement by GC–MS or LC–MSMS.

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Method validation by collaborative trial with participants from 10 countries.

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Method performance parameters are compliant with EU legislation on food contaminants.

Meat from male pigs may develop an off-flavour, commonly known as boar taint. Castration of male piglets prevents the potential formation of off-flavour.

In the suggested method, three marker compounds for boar taint (skatole, androstenone and indole) are quantified in pork fat by isotope dilution gas chromatography mass spectrometry (GC–MS) or by isotope dilution liquid chromatography tandem mass spectrometry (LC–MS/MS).

This method was validated by collaborative trial according to ISO 5725-2:1994. The studied concentration ranges included sensorial thresholds. The repeatability relative standard deviation (RSD_r) ranges from 3% to 10% and the reproducibility relative standard deviation (RSD_R) from 10% to about 30%.

The method has proven to be robust and free from matrix interferences.

The method performance characteristics are compliant with requirements for official control methods in the area of food contaminants; therefore, the method is regarded as fit for its intended purpose.

Valorisation of tainted boar meat in patties, frankfurter sausages and cooked ham by means of targeted dilution, cooking and smoking

Because of the need to abolish the castration of piglets without anaesthesia/analgesia, the pig industry is searching for a mode of action for the valorisation of meat with boar taint, an off-odour in entire male pigs. Carcasses with boar taint were selected by means of sensory and chemical analysis, after which patties with different levels of tainted boar meat were produced, as well as cooked ham and Frankfurter sausages using different smoke condensates and cooking temperatures. For these products orthonasal and retronasal boar taint odour were assessed by a trained expert panel. The results offer guidance regarding dilution of tainted meat (with <400 µg/kg androstenone if skatole is low or <200 µg/kg androstenone in concurrence with ≥37 µg/kg skatole) and the potential application of smoke condensates (e.g., Rudinsmoke C for sausages and Smokez LFBN for ham) as promising boar taint masking strategies.

Genomic background and genetic relationships between boar taint and fertility traits in German Landrace and Large White

BACKGROUND

Due to ethical reasons, surgical castration of young male piglets in their first week of life without anesthesia will be banned in Germany from 2021. Breeding against boar taint is already implemented in sire breeds of breeding organizations but in recent years a low demand made this trait economically less important. The objective of this study was to estimate heritabilities and genetic relationships between boar taint compounds androstenone and skatole and maternal/paternal reproduction traits in 4'924 Landrace (LR) and 4'299 Large White (LW) animals from nucleus populations. Additionally, genome wide association analysis (GWAS) was performed per trait and breed to detect SNP marker with possible pleiotropic effects that are associated with boar taint and fertility.

RESULTS

Estimated heritabilities (h²) were 0.48 (±0.08) for LR (0.39 ± 0.07 for LW) for androstenone and 0.52 (±0.08) for LR (0.32 ± 0.07 for LW) for skatole. Heritabilities for reproduction did not differ between breeds except age at first insemination (LR: h² = 0.27 (±0.05), LW: h² = 0.34 (±0.05)). Estimates of genetic correlation (r_g) between boar taint and fertility were different in LR and LW breeds. In LR an unfavorable r_g of 0.31 (±0.15) was observed between androstenone and number of piglets born alive, whereas this r_g in LW (- 0.15 (±0.16)) had an opposite sign. A similar breed-specific difference is observed between skatole and sperm count. Within LR, the r_g of 0.08 (±0.13) indicates no relationship between the traits, whereas the r_g of - 0.37 (±0.14) in LW points to an unfavorable relationship. In LR GWAS identified QTL regions on SSC5 (21.1-22.3 Mb) for androstenone and on SSC6 (5.5-7.5 Mb) and SSC14 (141.1-141.6 Mb) for skatole. For LW, one marker was found on SSC17 at 48.1 Mb for androstenone and one QTL on SSC14 between 140.5 Mb and 141.6 Mb for skatole.

CONCLUSION

Knowledge about such genetic correlations could help to balance conventional breeding programs with boar taint in maternal breeds. QTL regions with unfavorable pleiotropic effects on boar taint and fertility could have deleterious consequences in genomic selection programs. Constraining the weighting of these QTL in the genomic selection formulae may be a useful strategy to avoid physiological imbalances.

IDO3 and its successful bioaugmentation in activated sludge systems

Skatole is the key malodorous compound in livestock and poultry waste and wastewater with a low odor threshold. It not only causes serious nuisance to residents and workers, but also poses threat to the environment and human health due to its biotoxicity and recalcitrant nature. Biological treatment is an eco-friendly and cost-effective approach for skatole removal, while the bacterial resources are scarce. Herein, the Burkholderia strain was reported to efficiently degrade skatole for the first time. Results showed that strain IDO3 maintained high skatole-degrading performance under the conditions of pH 4.0-9.0, rotate speed 0-250 rpm, and temperature 30-35 °C. RNA-seq analysis indicated that skatole activated the oxidative phosphorylation and ATP production levels in strain IDO3. The oxidoreductase activity item which contained 373 differently expressed genes was significantly impacted by Gene Ontology analysis. Furthermore, the bioaugmentation experiment demonstrated that strain IDO3 could notably increase the removal of skatole in activated sludge systems. High-throughput 16S rRNA gene sequencing data indicated that the alpha-diversity and bacterial community tended to be stable in the bioaugmented group after 8 days operation. PICRUSt analysis indicated that xenobiotics biodegradation and metabolism, and membrane transport categories significantly increased, consistent with the improved skatole removal performance in the bioaugmented group. Burkholderia was survived and colonized to be the predominant population during the whole operation process (34.19-64.00%), confirming the feasibility of Burkholderia sp. IDO3 as the bioaugmentation agent in complex systems.

The evolutionarily conserved indolergic receptors of the non-hematophagous elephant mosquito Toxorhynchites amboinensis

The conservation of the mosquito indolergic receptors across the Culicinae and Anophelinae mosquito lineages, which spans 200 million years of evolution, is a testament to the central role of indolic compounds in the biology of these insects. Indole and skatole have been associated with the detection of oviposition sites and animal hosts. To evaluate the potential ecological role of these two compounds, we have used a pharmacological approach to characterize homologs of the indolergic receptors Or2 and Or10 in the non-hematophagous elephant mosquito Toxorhynchites amboinensis. We provide evidence that both receptors are narrowly tuned to indole and skatole like their counterparts from hematophagous mosquitoes. These findings indicate that Toxorhynchites detects indole and skatole in an ecological context to be determined and underscore the importance of understanding the role of these compounds in mosquitoes.

Mechanistic insight into the role of immunocastration on eliminating skatole in boars

The accumulation of skatole in fat tissue is one of the predominant factors, causing boar taint. The present study was aimed to understand the mechanism whereby active immunization against GnRH (immunocastration) eliminates skatole in boars. Thirty-six boars were assigned within litter into three groups (n = 12): control, surgically castrated, or immunized against GnRH at 10 wk of age (with a booster 8 wk later). Faecal and blood samples (for skatole and skatole-regulatory hormone profiles) were collected at 4-wk intervals until boars were slaughtered (26 weeks). Immunocastration reduced (P < 0.05) serum levels of androstenone, 17β-estradiol and IGF1 especially after the booster immunization, and down-regulated (P < 0.05) mRNA expressions of both IGF1 and IGF1receptor (IGF1R) in mucosa of ileum as well as colon at slaughter. Compared to intact controls, immunocastration substantially decreased (P < 0.05) faecal skatole contents subsequent to the decrease of serum IGF1 levels, which persisted in boars after surgical castration. In parallel with the decreased formation of skatole in the intestine, levels of skatole in serum and then in fat tissue were also decreased (P < 0.05). On the other hand, deprivation of testicular steroids, especially androstenone and 17β-estradiol accelerated skatole degradation metabolism in the liver by increasing (P < 0.05) hepatic CYP2E1, CYP2A, CYP2C49 and CYB5A expressions. Collectively, our results suggested that immunocastration decreased skatole formation in the intestine and meanwhile accelerated skatole degradation metabolism in the liver, resultantly eliminating skatole accumulation in male pigs. Decreased intestinal skatole formation by immunocastration appeared to be associated with the attenuated actions of IGF1 on the turnover of both ileal and colon mucosa.

Sustainable use of tainted boar meat: Blending is a strategy for processed products

While forming mixtures is a widely used approach for other raw materials in food industry, it has not yet been systematically analyzed for boar tainted meat. That is why we simultaneously studied four factors relevant for the production of emulsion-type sausages: percentage boar meat (skatole concentrations up to 0.3 μg/g, androstenone up to 3.8 μg/g in melted backfat), duration of traditional smoke and concentration levels of two spices. 16 variants of Frankfurters were produced in two independent studies and evaluated by in total 211 consumers. A linear mixed effects model revealed that increased levels of boar tainted meat significantly reduced consumer acceptance which could not be compensated by increased smoke or spice levels. We propose a non-inferiority test to identify the mixture which is similarly accepted as the reference made without boar tainted meat. Up to 33% tainted boar meat is proposed, assuming a liking drop of 0.5 on a 9 point liking scale as benchmark for an inferior product.

Development of a species-specific TaqMan-MGB real-time PCR assay to quantify Olsenella scatoligenes in pigs offered a chicory root-based diet

Olsenella scatoligenes is the only skatole-producing bacterium isolated from the pig gut. Skatole, produced from microbial degradation of l-tryptophan, is the main contributor to boar taint, an off-odor and off-flavor taint, released upon heating meat from some entire male pigs. An appropriate method for quantifying O. scatoligenes would help investigating the relationship between O. scatoligenes abundance and skatole concentration in the pig gut. Thus, the present study aimed at developing a TaqMan-MGB probe-based, species-specific qPCR assay for rapid quantification of O. scatoligenes. The use of a MGB probe allowed discriminating O. scatoligenes from other closely related species. Moreover, the assay allowed quantifying down to three target gene copies per PCR reaction using genomic DNA-constructed standards, or 1.5 × 10³ cells/g digesta, using O. scatoligenes-spiked digesta samples as reference standards. The developed assay was applied to assess the impact of dietary chicory roots on O. scatoligenes in the hindgut of pigs. Olsenella scatoligenes made up < 0.01% of the microbial population in the pig hindgut. Interestingly, the highest number of O. scatoligenes was found in young entire male pigs fed high levels of chicory roots. This indicates that the known effect of chicory roots for reducing skatole production is not by inhibiting the growth of this skatole-producing bacterium in the pig hindgut. Accordingly, the abundance of O. scatoligenes in the hindgut does not seem to be an appropriate indicator of boar taint. The present study is the first to describe a TaqMan-MGB probe qPCR assay for detection and quantification of O. scatoligenes in pigs.

The use of smoke as a strategy for masking boar taint in sausages and bacon

Smoke has often been recommended as a masking agent for boar taint. However, guidelines on how much smoke is necessary have not been established. We compared different smoking parameters in bacon (smoking times) and sausages (smoking times and use of liquid smoke). In streaky bacon from entire male pigs with skatole concentrations of up to 0.6 μg/g and androstenone concentrations of up to 5.8 μg/g in the neck fat, three smoking times were compared: 10, 30 and 60 min. Boar taint was partially, but not fully, masked. The longer the smoking time, the better the masking effect. In sausages from entire male pigs with an average skatole concentration of up to 0.6 μg/g and androstenone concentration of up to 3.6 μg/g (the meat part) or 2.4 μg/g (the fat part) in the neck fat, smoking for 40 and 80 min fully masked the boar taint, whereas only a minor effect was seen after 10 and 20 min smoking. Liquid smoke (0.1%) did not mask boar taint when added to sausages from entire male pigs with an average skatole concentration of 0.36 μg/g (meat) or 0.38 μg/g (fat) and androstenone concentration of 2.3 μg/g (meat) and 2.9 μg/g (fat). To effectively mask boar taint, an intense smoked flavour is therefore necessary, and the longer the smoking time, the better. In contrast, the use of liquid smoke mixed into the product was not effective in the concentrations used in the current study.

Consumer acceptance of minced meat patties from boars in four European countries

A consumer study was performed in four EU countries to further clarify the acceptability of meat with boar taint. In Denmark, France, Italy and Poland, a total of 476 female consumers evaluated 8 meat patties from boars with varying levels of skatole (0.10-0.40μg/g fat tissue) and androstenone (0.47-2.00 μg/g fat tissue), in a pair-wise comparison with patties from castrates. Boar meat patties were always less preferred than the castrate meat patties, regardless of the level of androstenone and skatole. Acceptability of the boar meat patties decreased with increasing skatole level. In samples with low skatole levels, higher levels of androstenone also reduced acceptability among androstenone sensitive consumers. No clear threshold levels for androstenone and skatole could be identified. Maps presenting the reduction in preference due to increasing levels of skatole and androstenone, and corrected for the general acceptance of the meat product were developed, taking into account androstenone sensitivity. Further work is needed, covering the whole range of androstenone and skatole levels found in entire male pigs and for a wider set of meat products.

Fine mapping of a QTL affecting levels of skatole on pig chromosome 7

BACKGROUND

Previous studies in the Norwegian pig breeds Landrace and Duroc have revealed a QTL for levels of skatole located in the region 74.7-80.5 Mb on SSC7. Skatole is one of the main components causing boar taint, which gives an undesirable smell and taste to the pig meat when heated. Surgical castration of boars is a common practice to reduce the risk of boar taint, however, a selection for boars genetically predisposed for low levels of taint would help eliminating the need for castration and be advantageous for both economic and welfare reasons. In order to identify the causal mutation(s) for the QTL and/or identify genetic markers for selection purposes we performed a fine mapping of the SSC7 skatole QTL region.

RESULTS

A dense set of markers on SSC7 was obtained by whole genome re-sequencing of 24 Norwegian Landrace and 23 Duroc boars. Subsets of 126 and 157 SNPs were used for association analyses in Landrace and Duroc, respectively. Significant single markers associated with skatole spanned a large 4.4 Mb region from 75.9-80.3 Mb in Landrace, with the highest test scores found in a region between the genes NOVA1 and TGM1 (p < 0.001). The same QTL was obtained in Duroc and, although less significant, with associated SNPs spanning a 1.2 Mb region from 78.9-80.1 Mb (p < 0.01). The highest test scores in Duroc were found in genes of the granzyme family (GZMB and GZMH-like) and STXBP6. Haplotypes associated with levels of skatole were identified in Landrace but not in Duroc, and a haplotype block was found to explain 2.3% of the phenotypic variation for skatole. The SNPs in this region were not associated with levels of sex steroids.

CONCLUSIONS

Fine mapping of a QTL for skatole on SSC7 confirmed associations of this region with skatole levels in pigs. The QTL region was narrowed down to 4.4 Mb in Landrace and haplotypes explaining 2.3% of the phenotypic variance for skatole levels were identified. Results confirmed that sex steroids are not affected by this QTL region, making these markers attractive for selection against boar taint.

Activation of the aryl hydrocarbon receptor decreases rifampicin-induced CYP3A4 expression in primary human hepatocytes and HepaRG

The role of the cross-talk between nuclear receptors in the regulation of Cytochrome P450 expression in the liver is well-documented. Most studies have focused on the cross-talk between the pregnane X receptor (PXR) and other receptors, such as the constitutive androstane receptor. However, cross-talk between PXRs and aryl hydrocarbon receptors (AhRs) has also been suggested, but reports regarding this cross-talk are conflicting. In the present study, we treated HepaRG and primary human hepatocytes (PHHs) with both a strong (TCDD) and weak (3-methylindole; 3MI) AhR activator to investigate their impact on PXR-regulated expression of CYP3A4. Moreover, we investigated the effect of co-activation of PXR, using rifampicin, and AhR, using TCDD and 3MI, on the regulation of CYP3A4 induction. We also investigated whether knockdown of AhR using siRNA affected the basal expression of PXR and CYP3A4 and induction of CYP3A4 by rifampicin, TCDD and 3MI. The results showed that the treatment of HepaRG cells, but not of PHHs, with AhR activators decreased mRNA expression of CYP3A4 and PXR. Moreover, in both HepaRG and PHHs, AhR activation decreased rifampicin-induced expression of CYP3A4 mRNA. Knock-down of AhR in PHHs increased both basal and rifampicin-induced expression of CYP3A4 mRNA. In conclusion, the presented results suggested that the cross-talk between PXR and AhR plays a role in the regulation of CYP3A4 gene expression.

Sensory evaluation of boar meat products by trained experts

Rearing entire male pigs, one of the alternatives for surgical castration, entails the possible occurrence of boar taint. This study aimed at the investigation of the acceptability of meat from entire male pigs in 8 different meat products (cutlets, bacon, blade loin, tenderloin, dry fermented sausage, cooked ham, dry-cured ham and minced meat) by trained assessors. Generally, the sensory evaluation of meat samples was affected the most in the androstenone (AEON) group, indicating that AEON is the most offensive boar taint compound for sensitive assessors. Differences between the meat products showed the highest potential for processing tainted meat in cold meat products, which was most likely due to the serving temperature on the one hand and production-related influences on the other. However, more insights regarding reducing and masking effects of production-related factors on boar taint are necessary.

Identification, quantification and treatment of fecal odors released into the air at two wastewater treatment plants

Odorous emissions from wastewater treatment plants (WWTPs) are an annoyance for neighboring communities. This article, for the first time, quantitatively reports on an evaluation of the presence of fecal odorants identified in air samples from two exemplary WWTPs by the odor profile method (OPM) and chemical analysis. The fecal odorants indole and skatole were identified by Gas Chromatography-Mass Spectrometry. The odor threshold concentration of skatole was determined to be 0.327 ng/L (60 pptV) in Teflon Bags by an expert panel. Skatole was found to be the primary chemical leading to fecal odor, due to its odor concentration to odor threshold concentration ratio that ranged from 2.8 to 22.5. The Weber-Fechner law was followed by pure skatole, but was not applicable when there was a mixture of fecal odorants and other odorant types present in WWTP air emission samples. This is probably caused by antagonism with other odorant types. Several existing odor control treatment methods for fecal odorants were evaluated at different wastewater treatment operations at two WWTPs by the OPM and chemical analysis for indole and skatole. Chemical scrubbing and biofiltration performed best in removing fecal odors among current control technologies.

Russian and Chinese consumers' acceptability of boar meat patties depending on their sensitivity to androstenone and skatole

The aim of this work was to study the sensitivity of Chinese and Russian female consumers to androstenone and skatole and to identify their preference for pork patties from entire male pigs compared with those from castrated pigs. One-hundred-twenty women in each country were enrolled. The sensitivity of the consumers to both compounds was tested using smell strips and triangular tests. Pairwise tests were performed comparing patties from castrated male pigs with patties from boars with different levels of androstenone and skatole. Approximately 70% of the Russian and 60% of the Chinese consumers were sensitive to skatole and 37% and 32% were sensitive to androstenone, respectively. Nevertheless, a higher percentage of sensitive Russian consumers compared to Chinese consumers disliked the smell of both compounds. In Russia, the consumers' preferences were higher for patties with low levels of both compounds, while no differences were found in China. In both countries, consumers who were sensitive to skatole also preferred patties with low levels of both compounds. Thus, the levels of androstenone and skatole affect boar patty preferences.

Effect of Bacillus subtilis Natto on Meat Quality and Skatole Content in TOPIGS Pigs

This study investigated the effect of Bacillus subtilis (B. subtilis) natto on meat quality and skatole in TOPIGS pigs. Sixty TOPIGS pigs were randomly assigned to 3 groups (including 5 pens per group, with 4 pigs in each pen) and fed with basic diet (control group), basic diet plus 0.1% B. subtilis natto (B group), and basic diet plus 0.1% B. subtilis natto plus 0.1% B. coagulans (BB group), respectively. All pigs were sacrificed at 100 kg. Growth performance, meat quality, serum parameters and oxidation status in the three groups were assessed and compared. Most parameters regarding growth performance and meat quality were not significantly different among the three groups. However, compared with the control group, meat pH24, fat and feces skatole and the content of Escherichia coli (E. Coli), Clostridium, NH3-N were significantly reduced in the B and BB groups, while serum total cholesterol, high density lipoprotein, the levels of liver P450, CYP2A6, and CYP2E1, total antioxidant capability (T-AOC) and glutathione peroxidase and Lactobacilli in feces were significantly increased in the B and BB groups. Further, the combined supplementation of B. subtilis natto and B. coagulans showed more significant effects on the parameters above compared with B. subtilis, and Clostridium, and NH3-N. Our results indicate that the supplementation of pig feed with B. subtilis natto significantly improves meat quality and flavor, while its combination with B. coagulans enhanced these effects.

Consumers' perception and acceptance of boiled and fermented sausages from strongly boar tainted meat

Characteristic off-flavours may occur in uncastrated male pigs depending on the accumulation of androstenone and skatole. Feasible processing of strongly tainted carcasses is challenging but gains in importance due to the European ban on piglet castration in 2018. This paper investigates consumers' acceptability of two sausage types: (a) emulsion-type (BOILED) and (b) smoked raw-fermented (FERM). Liking (9 point scales) and flavour perception (check-all-that-apply with both, typical and negatively connoted sensory terms) were evaluated by 120 consumers (within-subject design). Proportion of tainted boar meat (0, 50, 100%) affected overall liking of BOILED, F (2, 238)=23.22, P<.001, but not of FERM sausages, F (2, 238)=0.89, P=.414. Consumers described the flavour of BOILED-100 as strong and sweaty. In conclusion, FERM products seem promising for processing of tainted carcasses whereas formulations must be optimized for BOILED in order to eliminate perceptible off-flavours. Boar taint rejection thresholds may be higher for processed than those suggested for unprocessed meat cuts.

Feasibility of boar taint classification using a portable Raman device

The feasibility of Raman spectroscopy for boar taint detection and classification was investigated using tainted and untainted backfat samples of 46 boars. For this exploratory study, backfat samples were selected according to their levels of androstenone and skatole as determined by gas chromatography and their sensory score by a trained panel. Raman spectra were collected with a portable device at freshly cut surfaces of frozen-thawed samples. Both inner and outer layers of subcutaneous fat were studied. Their varying level of unsaturation was reflected in the Raman spectra. Partial least squares regression discriminant analysis (PLS-DA) was applied to the spectra together with various pre-processing methods. A model using only spectra obtained at the inner layer resulted in the highest classification accuracy for boar taint (81% of samples correctly classified). The discrimination is shown to reflect differences in the degree of fatty acid saturation between tainted and untainted boars. In conclusion, the findings suggest that with further development Raman spectroscopy may be used to classify boar taint.

Consumers' segmentation based on the acceptability of meat from entire male pigs with different boar taint levels in four European countries: France, Italy, Spain and United Kingdom

Two consumer studies were conducted to know the acceptability of pork with different boar taint levels: test 1 performed in Spain (n=126) and United Kingdom (n=146), and test 2 performed in France (n=139) and Italy (n=140). Each test had 3 types of pork: 'Female meat', 'Low boar tainted meat', and a third type was 'Medium boar tainted meat' or 'High boar tainted meat'. Three main clusters were identified on the basis of 'How delicious do you find this meat?': 1-Pork lovers, 2-Boar meat lovers, 3-Reject boar tainted meat. Additionally, in test 2, a fourth cluster was identified: 'Reject low tainted meat'. A group of 16.2-38.2% of consumers rejected meat from boars, and another group of 12.4-21.7% rated the meat with medium or high levels of boar taint better than the meat from females, identifying a niche for meat from medium and high levels of boar taint, and suggesting the need to select carcasses on the basis of boar taint.

Prevalence of boar taint in commercial pigs from Spanish farms

The presence of boar taint can affect the sensory quality of pork because the "off" odours and flavours can be detected by consumers. The aim of this study was to determine the prevalence of boar taint in pig carcasses from 30 Spanish farms located in different regions of the country. Hot carcass weight and subcutaneous fat thickness means were 79.4±8.19 kg and 18.4±5.09 mm, respectively. Subcutaneous fat samples were classified into different levels according to androstenone and skatole concentrations in adipose tissue measured using GC-MS and HPLC. Androstenone results were: 87.4% of the carcasses below 0.50 μg/g, 7.1% from 0.50 to 1.00 μg/g (medium level), and 5.5% ≥1.00 μg/g (high level). Skatole results were: 88.9% of the carcasses below 0.10 μg/g, 4.5% from 0.10 to 0.20 μg/g (medium level), and 6.6% ≥0.20 μg/g (high level). Given these results, a future online method to classify carcasses according to boar taint is strongly recommended.

Influence of sampling procedure, sampling location and skin contamination on skatole and indole concentrations in adipose tissue of pigs

Skatole leads to off-odor in pork and is influenced by several factors such as sex and management conditions of pigs, but the causal relationships have not yet been clarified. In the present study, physiological skatole concentrations along the carcass were monitored and the transdermal diffusion of skatole was experimentally studied with skatole-spiked feces. Additionally, the impact of different biopsy techniques on skatole in fat and blood was studied. Monitoring of skatole along the carcass revealed higher skatole concentrations in the belly than in dorsal cuts. Topical application of spiked feces increased skatole in fat strictly at the application site. In contrast to punch biopsies, surgical biopsies significantly affected skatole and cortisol levels in blood, but not in fat. We conclude that biopsies for skatole measurements should be taken without anesthesia from the dorsal side of the animals. Fecal contaminations on the ventral side are not likely to influence overall concentrations.

Boar taint detection: A comparison of three sensory protocols

While recent studies state an important role of human sensory methods for daily routine control of so-called boar taint, the evaluation of different heating methods is still incomplete. This study investigated three common heating methods (microwave (MW), hot-water (HW), hot-iron (HI)) for boar fat evaluation. The comparison was carried out on 72 samples with a 10-person sensory panel. The heating method significantly affected the probability of a deviant rating. Compared to an assumed 'gold standard' (chemical analysis), the performance was best for HI when both sensitivity and specificity were considered. The results show the superiority of the panel result compared to individual assessors. However, the consistency of the individual sensory ratings was not significantly different between MW, HW, and HI. The three protocols showed only fair to moderate agreement. Concluding from the present results, the hot-iron method appears to be advantageous for boar taint evaluation as compared to microwave and hot-water.

Effects of L-tryptophan, Fructan, and Casein on Reducing Ammonia, Hydrogen Sulfide, and Skatole in Fermented Swine Manure

The effects of daily dietary Bacillus subtilis (Bs), and adding L-tryptophan, fructan, or casein to fecal fermentation broths were investigated as means to reduce the production of noxious gas during manure fermentation caused by ammonia, hydrogen sulfide (H2S), and 3-methylindole (skatole). Eighty swine (50.0±0.5 kg) were equally apportioned to an experimental group given Bs in daily feed, or a control group without Bs. After 6 weeks, fresh manure was collected from both groups for fermentation studies using a 3×3 orthogonal array, in which tryptophan, casein, and fructan were added at various concentrations. After fermentation, the ammonia, H2S, L-tryptophan, skatole, and microflora were measured. In both groups, L-tryptophan was the principle additive increasing skatole production, with significant correlation (r = 0.9992). L-tryptophan had no effect on the production of ammonia, H2S, or skatole in animals fed Bs. In both groups, fructan was the principle additive that reduced H2S production (r = 0.9981). Fructan and Bs significantly interacted in H2S production (p = 0.014). Casein was the principle additive affecting the concentration of ammonia, only in the control group. Casein and Bs significantly interacted in ammonia production (p = 0.039). The predominant bacteria were Bacillus spp. CWBI B1434 (26%) in the control group, and Streptococcus alactolyticus AF201899 (36%) in the experimental group. In summary, daily dietary Bs reduced ammonia production during fecal fermentation. Lessening L-tryptophan and increasing fructan in the fermentation broth reduced skatole and H2S.

Hydrolysable tannin fed to entire male pigs affects intestinal production, tissue deposition and hepatic clearance of skatole

The effect of adding hydrolysable tannins to the diet of fattening boars was studied. Performance, reproductive organ weights, salivary gland morphology, boar taint compounds and skatole metabolism were evaluated. At 123 days of age and 52 ± 6 kg liveweight, 24 Landrace × Large White boars were assigned within a litter to four treatment groups: control (T0 fed mixture with 13.2 MJ/kg, 17.5% crude proteins) and three experimental diets for which the T0 diet was supplemented with 1%, 2% and 3% of hydrolysable tannin-rich extract (T1, T2 and T3, respectively). Pigs were kept individually with ad libitum access to feed and water and slaughtered at 193 days of age and 122 ± 10 kg liveweight. Adding hydrolysable tannins to the diet had no negative effect on growth performance at 1% and 2%, whereas the 3% inclusion reduced feed intake and resulted in an adaptive response of the salivary glands (particularly parotid gland hypertrophy). Relative to T0, fat tissue skatole concentration was increased in the T1 group, but was similar in T2 and T3. Across treatments tissue skatole concentrations were proportional to the activity of hepatic CYP450. The results indicate the potential of tannin supplementation to reduce boar taint although further investigations are needed in order to establishing optimal dosage.

Evaluating the performance of sensory quality control: the case of boar taint

Detection of malodours referred to as 'boar taint' in entire male pigs is essential for quality control when refraining piglet castration. This study analysed the sensitivity and specificity of sensory evaluation by trained assessors (n=18) compared to chemical analysis of two marker compounds (androstenone, skatole) in backfat (n=794). Taking the measurement uncertainty into consideration, several cut-off thresholds for chemical analysis were exemplarily evaluated. Using the panel average score, sensitivity and specificity of sensory analysis ranged from 61 to 69% and 77 to 85%, respectively. Performance of individual assessors varied highly (sensitivity: 47 to 86%; specificity: 45 to 88%) and correlated to olfactory acuity to the compounds. According to receiver operating characteristic-curves, the average panel performed better than single assessors regardless of the sensory criterion shift. Agreement plots illustrate that high skatole levels are better detected than high androstenone levels (useful for assessor feedback). The agreement between sensory and chemical analyses was moderate. Assessors need to be selected carefully.

Fatty acid composition of subcutaneous adipose tissue from entire male pigs with extremely divergent levels of boar taint compounds--an exploratory study

This exploratory study investigated the variability of fatty acid composition in entire male pigs with extremely divergent levels of boar taint compounds. Fatty acids were quantified in back fat samples from 20 selected carcasses of Pietrain*F1 sired boars (average carcass weight 84 kg) with extremely low (LL) or extremely high (HH) levels of androstenone, skatole, and indole. Concentrations of polyunsaturated fatty acids (PUFA) were significantly (p<0.05) increased in LL boars (23.4%) compared to HH boars (19.7%). This was mainly due to increased levels of linoleic acid (C18:2 n-6) and α-linolenic acid (C18:3 n-3). Correspondingly, unsaturated fatty acids (SFA) were significantly lower (p<0.05) in LL boars (35.2%) compared to HH boars (37.7%). The findings are discussed with respect to potential effects on flavor formation in boar fat and meat. Further research is needed to study the gender specificity and the interplay of the synthesis and the metabolism of steroids, lipids, and the clearance of skatole in pigs.

How olfactory acuity affects the sensory assessment of boar fat: a proposal for quantification

Due to animal welfare concerns the production of entire male pigs is one viable alternative to surgical castration. Elevated levels of boar taint may, however, impair consumer acceptance. Due to the lack of technical methods, control of boar taint is currently done using sensory quality control. While the need for control measures with respect to boar taint has been clearly stated in EU legislation, no specific requirements for selecting assessors have yet been documented. This study proposes tests for the psychophysical evaluation of olfactory acuity to key volatiles contributing to boar taint. Odor detection thresholds for androstenone and skatole are assessed as well as the subject's ability to identify odorants at various levels through easy-to-use paper smell strips. Subsequently, fat samples are rated by the assessors, and the accuracy of boar taint evaluation is studied. Considerable variation of olfactory performance is observed demonstrating the need for objective criteria to select assessors.

Fast and solvent-free quantitation of boar taint odorants in pig fat by stable isotope dilution analysis-dynamic headspace-thermal desorption-gas chromatography/time-of-flight mass spectrometry

Boar taint is a specific off-odour of boar meat products, known to be caused by at least three unpleasant odorants, with very low odour thresholds. Androstenone is a boar pheromone produced in the testes, whereas skatole and indole originate from the microbial breakdown of tryptophan in the intestinal tract. A new procedure, applying stable isotope dilution analysis (SIDA) and dynamic headspace-thermal desorption-gas chromatography/time-of-flight mass spectrometry (dynHS-TD-GC/TOFMS) for the simultaneous quantitation of these boar taint compounds in pig fat was elaborated and validated in this paper. The new method is characterised by a simple and solvent-free dynamic headspace sampling. The deuterated compounds d3-androstenone, d3-skatole and d6-indole were used as internal standards to eliminate matrix effects. The method validation performed revealed low limits of detection (LOD) and quantitation (LOQ) with high accuracy and precision, thus confirming the feasibility of the new dynHS-TD-GC/TOFMS approach for routine analysis.