Rapid high-performance liquid chromatographic method for simultaneous determination of androstenone, skatole and indole in back fat from pigs

Enhanced HPLC Method for Boar Taint Quantification

Boar taint is an unpleasant odour found in the carcasses of entire male pigs, resulting from androstenone and skatole accumulation during pubertal development, and impacting pork quality. This study proposes the validation of an adapted chromatographic method for quantifying skatole and androstenone in the pigs' liquid fat using fluorescence detection. A good chromatographic separation was achieved, with skatole (SKA) and androstenone (AND) elution at 4.4 and 9.9 min., respectively. An external calibration method was applied, with calibration curves correlation coefficient of 0.9999 for both analytes. Detection limit values were 1.53 and 16.02 ng/g for SKA and AND, respectively. SKA recovery was 99.72±2.34 % (2.34 % RSD) and 102.84±1.62 % (1.57 % RSD) for AND. Results showed good precision values (repeatability <2.46 % RSD for SKA, <6.85 % RSD for AND; intermediate precision <2.87 % RSD for SKA, <6.98 % RSD for AND). The method's robustness was tested and the values were within the reference ranges. The validation results proved that the adaptation of an existing method resulted in good assessments of robustness, reliability and accuracy.

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.

Effect of Immunocastration on Culled Sows-A Preliminary Study on Reproductive Tract, Carcass Traits, and Meat Quality

The Bísaro pig is a Portuguese autochthonous breed greatly appreciated for its meat quality and is mainly reared outdoors. Immunocastration could be a solution to avoid undesirable pregnancies and boar taint in cull sows. The present study tested three immunocastration protocols (with Improvac®) according to their reproductive cycle. The first inoculation was performed two weeks after farrowing (IM1, n = 5), at the beginning of estrus (IM2, n = 5), and one week after the end of estrus (IM3, n = 5), followed by a second administration four weeks apart. A control group (C, n = 5) was also included in the same housing conditions. The sample collection included the reproductive tract for morphometric evaluation, neck fat for the quantification of boar taint compounds, and a portion of the Longissimus thoracis et lumborum for meat quality trait assessment. The reproductive tracts from intact sows (C) were significantly heavier compared to the immunocastrated groups (p < 0.05) (1.403 kg C to 0.508 kg IM1, 0.590 kg IM2, and 0.599 kg IM3), suggesting the regression of the reproductive tract to nonstimulated conditions due to immunization against GnRH. The IM1 group exhibited significantly smaller reproductive tract measurements compared to group C for most of the evaluated segments (p < 0.05). No marked differences were observed in the meat quality traits. Therefore, immunocastration can be used in culling sows to avoid ovarian activity, and it is not detrimental to pork quality traits.

Outdoor Finishing of Intact Male Portuguese Alentejano Pigs on a Sustainable High-Fiber Diet: Impacts on Blood, Growth, Carcass, Meat Quality and Boar Taint Compounds

This trial evaluated the effect of sex on the blood, growth, carcass, meat quality, and boar taint compounds in male Alentejano (AL) pigs (n = 30). From ~40 to 130 kg LW, castrated (C) and intact pigs (I and IExp groups) were fed commercial diets ad libitum. Between ~130 and 160 kg (slaughter), C and I pigs continued on commercial diets, while IExp were fed an experimental diet containing locally produced pulses and by-products aimed at reducing boar taint. At ~160 kg, blood urea levels were higher in IExp than C pigs, triacylglycerols were lower in both intact groups, and cortisol was lower in IExp. IExp pigs exhibited faster growth, improved feed conversion ratio, carcass higher commercial yield and leaner meat than C pigs. The loin intramuscular fat in intact pigs was lower, less saturated and more polyunsaturated, while total collagen was higher. Fat androstenone content was higher in intact pigs and skatole content was similar across treatments, although they were below threshold values for consumer detection. Finally, although boar taint compounds were low in intact AL pigs raised outdoors, adding pulses and by-products to the experimental diet did not result in a reduction in fat skatole content compared to pigs fed the commercial diet.

Lipid Serum Profiling of Boar-Tainted and Untainted Pigs Using GC×GC-TOFMS: An Exploratory Study

Mass spectrometry (MS)-based techniques, including liquid chromatography coupling, shotgun lipidomics, MS imaging, and ion mobility, are widely used to analyze lipids. However, with enhanced separation capacity and an optimized chemical derivatization approach, comprehensive two-dimensional gas chromatography (GC×GC) can be a powerful tool to investigate some groups of small lipids in the framework of lipidomics. This study describes the optimization of a dedicated two-stage derivatization and extraction process to analyze different saturated and unsaturated fatty acids in plasma by two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) using a full factorial design. The optimized condition has a composite desirability of 0.9159. This optimized sample preparation and chromatographic condition were implemented to differentiate between positive (BT) and negative (UT) boar-tainted pigs based on fatty acid profiling in pig serum using GC×GC-TOFMS. A chemometric screening, including unsupervised (PCA, HCA) and supervised analysis (PLS-DA), as well as univariate analysis (volcano plot), was performed. The results suggested that the concentration of PUFA ω-6 and cholesterol derivatives were significantly increased in BT pigs, whereas SFA and PUFA ω-3 concentrations were increased in UT pigs. The metabolic pathway and quantitative enrichment analysis suggest the significant involvement of linolenic acid metabolism.

Influence of Immunocastration and Diet on Meat and Fat Quality of Heavy Female and Male Pigs

Two experiments were carried out; one with female pigs and the other with male pigs destined for Teruel dry-cured ham production, to evaluate the effect of immunocastration (entire gilts-EG vs. immunocastrated gilts-IG and surgically castrated males vs. immunocastrated males-IM) and diet (control vs. high energy vs. low crude protein and amino acids) on meat quality and fat composition. Fifteen meat samples and eight fat samples of each treatment were analyzed in both experiments. In the case of males, six fat samples per treatment were analyzed to determine boar taint. Immunocastration is a good strategy in gilts intended for dry-cured ham production because improves meat composition; however, in males, immunocastration impairs the results of pork chemical composition compared with surgical castration. The IG presented a lower polyunsaturated/saturated fatty acids ratio than EG, improving fat technological quality. Diets had little effect on pork or fat quality in gilts, but a high-energy level using oilseeds and a low-crude-protein and -amino-acids diet from 80 to 137 kg of body weight could be interesting in IM to maintain or increase fat consistency, respectively. Moreover, in general, immunocastration is effective in avoiding boar taint in males.

The Uptake and Deconjugation of Androstenone Sulfate in the Adipose Tissue of the Boar

Boars express high testicular levels of sulfotransferase enzymes, and consequently, the boar taint causing compound androstenone predominantly circulates as a steroid sulfate. Androstenone sulfate is suspected to function as a steroid reservoir that can be deconjugated to provide a source of free androstenone for accumulation. Therefore, the purpose of this study was to characterize the uptake and deconjugation of androstenone sulfate in the adipose tissue of the boar. Real-time PCR was used to quantify the expression of steroid sulfatase (STS) and several organic anion transporting polypeptides (OATPs) in the adipose tissue. Additionally, [³H]-androstenone sulfate was incubated with adipocytes or supernatant from homogenized fat to assess steroid uptake and conversion, respectively. A positive correlation existed between OATP-B expression and androstenone sulfate uptake (r = 0.86, p = 0.03), as well as between STS expression and androstenone sulfate conversion (r = 0.76, p < 0.001). Moreover, fat androstenone concentrations were positively correlated (r = 0.85, p < 0.001) with androstenone sulfate conversion and tended to increase with STS expression in early maturing boars. This suggests that androstenone sulfate uptake and deconjugation are mediated by OATP-B and STS, respectively, which may influence the development of boar taint in early maturing animals.

Effect of Dietary Supplementation with Dried Tuber of Jerusalem Artichoke on Skatole Level in Backfat and CYP2E1 mRNA Expression in Liver of Boars

The objective of this study was to investigate the effect of diets containing different levels of dried tuber of Jerusalem artichoke, Helianthus tuberosus, on skatole levels in backfat and on the CYP2E1 mRNA expression in the liver of commercial crossbred pigs. A total of 23 uncastrated male pigs from 10 litters of a commercial crossbred population of Large White × (Landrace × Large White), were used in this study. Boars were randomly divided into four different dietary treatment groups – a control group (K1; 5 boars; without supplementation of Jerusalem artichoke) and three experimental groups (6 boars each) that were fed with the diet containing different levels of dried Jerusalem artichoke (K2 – 4.1%; K3 – 8.2%; K4 – 12.2%) for 14 days before slaughter. Significant effects of diet on skatole levels were observed between the control group and the experimental groups (P = 0.0078). The lowest level of skatole was in the K3 group with 8.2% of Jerusalem artichoke. As for CYP2E1, a negative correlation was observed between the levels of skatole and CYP2E1 mRNA expression. Significant effect (P = 0.0055) was found in all experimental groups compared to the K1 group, and most pronounced in the K2 and K3 groups. The supplementation with Jerusalem artichoke resulted in lower level of skatole and higher CYP2E1 mRNA expression. The results suggest that affecting the expression of CYP2E1 by feed supplements could be an option to effectively reduce the levels of skatole in adipose tissue of entire male pigs.

Comprehensive SPME-GC-MS Analysis of VOC Profiles Obtained Following High-Temperature Heating of Pork Back Fat with Varying Boar Taint Intensities

Boar taint detection is a major concern for the pork industry. Currently, this taint is mainly detected through a sensory evaluation. However, little is known about the entire volatile organic compounds (VOCs) profile perceived by the assessor. Additionally, many research groups are working on the development of new rapid and reliable detection methods, which include the VOCs sensor-based methods. The latter are susceptible to sensor poisoning by interfering molecules produced during high-temperature heating of fat. Analyzing the VOC profiles obtained by solid phase microextraction gas chromatography–mass spectrometry (SPME-GC-MS) after incubation at 150 and 180 °C helps in the comprehension of the environment in which boar taint is perceived. Many similarities were observed between these temperatures; both profiles were rich in carboxylic acids and aldehydes. Through a principal component analysis (PCA) and analyses of variance (ANOVAs), differences were highlighted. Aldehydes such as (E,E)-nona-2,4-dienal exhibited higher concentrations at 150 °C, while heating at 180 °C resulted in significantly higher concentrations in fatty acids, several amide derivatives, and squalene. These differences stress the need for standardized parameters for sensory evaluation. Lastly, skatole and androstenone, the main compounds involved in boar taint, were perceived in the headspace at these temperatures but remained low (below 1 ppm). Higher temperature should be investigated to increase headspace concentrations provided that rigorous analyses of total VOC profiles are performed.

The Binding of Free and Sulfated Androstenone in the Plasma of the Boar

Simple Summary

Boar taint is characterized by an off-odor or off-flavor in heated pork products that is caused by the accumulation of androstenone in the fat. We have previously demonstrated that androstenone is transported to the fat bound by the plasma protein albumin; however, it is unclear if androstenone sulfate, which is more abundant in the circulation, is transported in the same manner and if the transport of androstenone in the plasma influences the degree of accumulation in the fat. In this article, we determined that androstenone sulfate bound minimally in the plasma of the boar and suggested that this may leave it readily available to enter peripheral tissues, such as the fat where it may enzymatically return free androstenone. Additionally, we demonstrated that the binding of androstenone in the plasma varies significantly between boars with high and low concentrations of androstenone in the fat. This suggests that the binding of androstenone to albumin in the plasma affects the transport and distribution of androstenone within the boar.

Abstract

Androstenone circulates in the plasma bound to albumin before accumulating in the fat, resulting in the development of boar taint. Androstenone sulfate is more abundant in the circulation than free androstenone; however, it is unclear how androstenone sulfate is transported in the plasma and if steroid transport affects the development of boar taint. Therefore, the purpose of this study was to characterize the binding of androstenone sulfate in boar plasma and determine if variability in steroid binding affects the accumulation of androstenone in the fat. [³H]-androstenone sulfate was incubated with plasma and the steroid binding was quantified using gel filtration chromatography. Inter-animal variability was assessed by quantifying androstenone binding specificity in plasma obtained from boars that had high or low fat androstenone concentrations at slaughter. Androstenone sulfate bound minimally in the plasma and to isolated albumin, which suggests that it is transported primarily in solution. The specific binding of androstenone quantified in plasma and isolated albumin from low fat androstenone animals was significantly higher (p = 0.01) than in high fat androstenone boars. These results indicate that the binding of androstenone to albumin varies amongst individual animals and affects the transport of androstenone in the plasma and accumulation in the fat of the boar.

Influence of Immunocastration on Slaughter Traits and Boar Taint Compounds in Pigs Originating from Three Different Terminal Sire Lines

Simple Summary

Due to the negative public opinion and welfare issues related to surgical castration, gradual introduction of alternatives like entire males and immunocastrates is taking place. Despite several economical and welfare advantages that the alternatives offer, numerous issues (i.e., boar taint, meat quality alterations), as well as their interactions with rearing and breeding (genetic) factors remain unanswered. Therefore, the focus of this study was to investigate the possibility of using different commercial sire lines in three male sex categories (entire males, immunocastrates, surgical castrates) and to compare their carcass traits, meat quality and boar taint compounds. A significant effect of terminal sire line and/or male category together with their interaction was observed for most of the investigated carcass and meat quality traits. The observed interaction should be taken into consideration when deciding on the production of a specific male category.

Abstract

The aim of the research was to investigate the influence of terminal sire line (TSL) and male category (MC) on carcass and meat quality of commercial fatteners. The study was performed on 180 pigs originating from three terminal sire lines: A (Pietrain × Large White), B (pure Pietrain), and C (Pietrain × Duroc × Large White), being assigned to three groups according to MC: immunocastrates (IC, n = 60), surgical castrates (SC, n = 60) and entire males (EM, n = 60). TSL affected most of the carcass and meat quality traits, together with the androstenone concentration. At the same time, MC had a significant effect on fat thickness, ham circumference, drip loss, cooking loss and androstenone and skatole concentrations. A significant interaction effect was observed for carcass length and ham circumference, as well as for most of the measured meat quality traits (except cooking loss, CIE L*, CIE b*, and Warner Bratzler Shear Force (WBSF)). Among the three investigated sire lines, immunocastration was shown to be most beneficial for fatteners sired by the TSL C. However, if deciding to raise EM, fatteners from the TSL B are recommended in terms of carcass and meat quality, although strategies for avoiding boar taint in their carcasses must be taken into consideration.

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%.

Characterization of eQTLs associated with androstenone by RNA sequencing in porcine testis

Characterization of genetic variants affecting genome-wide gene expression levels (expression quantitative trait loci or eQTLs) in pig testes may improve our understanding of genetic architecture of boar taint (an animal welfare trait) and helps in genome-assisted or genomic selection programs. The aims of this study were to identify eQTLs associated with androstenone, to find candidate eQTLs for low androstenone, and to validate the top eQTL by reverse transcriptase quantitative PCR (RT-qPCR). Gene expression profiles were obtained by RNA sequencing in testis from Danish cross-bred pigs and genotype data by 80K single nucleotide polymorphism panel. A total of 262 eQTLs [false discovery rate (FDR) < 0.05] were identified by using two software packages: Matrix eQTL and Krux eQTL. Of these, 149 cis-acting eQTLs were significantly associated with androstenone concentrations and gene expression (FDR < 0.05). The eQTLs were associated with several genes of boar taint relevance including CYP1A2, CYB5D1, and SPHK2. One eQTL gene, AMPH, was differentially expressed (FDR < 0.05) and affected by chicory. Five candidate eQTLs associated with low androstenone concentrations were discovered, including the top eQTL associated with CYP1A2. RT-qPCR confirmed target gene expression to be significantly (P < 0.05) different based on eQTL genotypes. Furthermore, eQTLs were enriched as QTLs for 15 boar taint related traits from the PigQTLdb. This is the first study to report eQTLs in testes of commercial crossbred pigs used in pork production and to reveal genetic architecture of boar taint. Potential applications include development of a DNA test and in advanced genomic selection models for boar taint.

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.

Hydrolysable tannin-based diet rich in gallotannins has a minimal impact on pig performance but significantly reduces salivary and bulbourethral gland size

Tannins have long been considered ‘anti-nutritional’ factors in monogastric nutrition, shown to reduce feed intake and palatability. However, recent studies revealed that compared with condensed tannins, hydrolysable tannins (HT) appear to have far less impact on growth performance, but may be inhibitory to the total activity of caecal bacteria. This in turn could reduce microbial synthesis of skatole and indole in the hindgut of entire male pigs (EM). Thus, the objective of this study was to determine the impact of a group of dietary HT on growth performance, carcass traits and boar taint compounds of group housed EM. For the study, 36 Swiss Large White boars were assigned within litter to three treatment groups. Boars were offered ad libitum one of three finisher diets supplemented with 0 (C), 15 (T15) or 30 g/kg (T30) of HT from day 105 to 165 of age. Growth performance, carcass characteristics, boar taint compounds in the adipose tissue and cytochrome P450 (CYP) isoenzymes CYP2E1, CYP1A2 and CYP2A19 gene expression in the liver was assessed. Compared with C, feed efficiency but not daily gain and daily feed intake was lower (P<0.05) in T15 and T30 boars. Except for the percentage carcass weight loss during cooling, which tended (P<0.10) to be greater in T30 than C and T15, carcass characteristics were not affected by the diets. In line with the numerically lower androstenone level, bulbourethral and salivary glands of T30 boars were lighter (P<0.05) than of T15 with intermediate values for C. Indole level was lower (P<0.05) in the adipose tissue of T30 than C pigs with intermediate levels in T15. Skatole levels tended (P<0.10) to be lower in T30 and C than T15 pigs. Hepatic gene expression of CYP isoenzymes did not differ between-treatment groups, but was negatively correlated (P<0.05) with androstenone (CYP2E1 and CYP1A2), skatole (CYP2E1, CYP2A) and indole (CYP2A) level. In line with the numerically highest androstenone and skatole concentrations, boar taint odour but not flavour was detected by the panellists in loins from T15 compared with loins from C and T30 boars. These results provide evidence that HT affected metabolism of indolic compounds and androstenone and that they affected the development of accessory sex glands. However, the effects were too small to be detected by sensory evaluation.

Effect of piglet castration with nonsurgical sterilant on the zootechnical performance and pork carcass quality

ABSTRACT A non-surgical sterilant (NSS) was used with the objective of assessing the zootechnical performance, carcass and meat quality, and hormone levels. 90 male piglets were selected with birthweights varying between 1.5kg to 2.0kg. The control group was constituted of 45 males castrated by the conventional surgical method, at the seventh day of age, and the treated group was constituted of 45 males castrated with NSS (active principle of zinc gluconate in the concentration of 26.2mg/mL associated to the dimethyl sulfoxide at 0.5%), with the application of the first dose on the seventh day of age and the second dose on the fourteenth day of age. The zootechnical assessments were carried out on the farm and consisted: weight gain in the periods per animal and feed conversion. The slaughter of the animals and the assessment of the carcass and meat quality and hormone levels were carried out in a slaughterhouse and the municipality of Campinas (SP). The study demonstrated that the use of NSS was a viable alternative in relation to the zootechnical performance and the carcass quality. In relation to the meat quality there was no significant difference in the majority of the assessed parameters.

Effect of non-starch polysaccharides on production and absorption of indolic compounds in entire male pigs

In order to study the effect of feeding non-starch polysaccharides (NSP) on the production and absorption of the malodorous compounds skatole and indole, eighteen male pigs, representing nine littermate groups, were used. One pig from each litter was assigned to either a low-NSP diet (87 g/kg of NSP) or a high-NSP diet (160 g/kg of NSP). Faecal samples and blood samples from vena jugularis were collected during a three-day period. The production of indolic compounds in different sections of the gastro-intestinal tract of six littermate groups was measured at slaughter (after 1 month on the diets). To investigate the absorption of indole and skatole, three catheterized pigs, acting as their own control (2 weeks on each diet) were used. Parallel determinations in portal blood, peripheral blood and in faeces of skatole and indole were conducted. Faecal, intestinal and blood samples were analysed for indolic compounds by high-performance liquid chromatography (HPLC). The production of indole and skatole in the proximal and distal part of the hind gut, respectively, was significantly reduced in pigs given the high-NSP diet. Similarly, both blood and faecal samples revealed that dietary NSP-inclusion reduced skatole concentration, whereas a dietary effect of NSP on the indole concentration was reflected in blood samples only. The absorption of skatole and indole was significantly lower in pigs given the high-NSP diet compared with those offered the low-NSP diet. The skatole concentrations in blood and faeces were highly correlated when measured within the individual animal, suggesting that a proportional amount of the skatole produced was absorbed. In contrast, only weak correlations were demonstrated when determined between animals. This emphasizes the great impact that individual hepatic clearance rate would have on the level of skatole in backfat, and consequently the importance of applying cross-over designs, when studying the absorption of indolic compounds.

Estimates of genetic parameters for content of boar taint compounds in adipose tissue of intact males at 160 and 220 days of age

The aims of this study were to investigate variation in content of androstenone (AND), skatole (SKA), and indole (IND), quantified in adipose tissue of intact male pigs at 160 d of age (105 kg BW) and 220 d of age (155 kg BW), to estimate genetic parameters and to investigate the genetic relationships for AND, SKA, IND, and growth traits. A sample of adipose tissue was collected in vivo, using a biopsy device, from the neck of 500 intact males at the 2 ages and at slaughter from the ham of 100 of the investigated animals. Backfat depth was measured at 220 d of age, whereas BW was recorded at each sampling. Quantification of AND, SKA, and IND was performed by HPLC with fluorescence detection. Estimates of genetic parameters were obtained through Bayesian analyses after logarithmic transformations of original measures. Contents of boar taint compounds (BTC) measured at 220 d were higher than those at 160 d of age. Correlations between contents of BTC in backfat and ham fat ranged from 0.7 (IND) to 0.88 (SKA). Medium-high h were estimated for BTC at both ages, but estimates at 220 d (0.58, 0.60, and 0.69 for AND, SKA, and IND, respectively) were greater than those at 160 d. The genetic correlation between contents at 160 and 220 d of each BTC was positive, but the probability that such estimates were greater than 0.8 was very low, indicating that contents at 160 and 220 d were traits controlled by different genetic backgrounds. Different rankings were observed when breeding values for the content at 160 and 220 d of age were used to rank animals. As a consequence, performance testing programs for BTC should be based preferably on phenotypes measured at 220 d of age. Weak genetic correlations were observed between content of BT compounds and growth traits (BW, backfat depth, and daily gain from 160 to 220 d of age), indicating that selective breeding to reduce the risk of tainted pork is expected to exert trivial effects on growth performance and fat deposition. Results indicate that prevalence of BTC is high in mature and heavy pigs relative to young and light pigs. High heritability; positive genetic correlations between AND, SKA, and IND; and trivial effects on growth traits suggest that reduction of BTC through selective breeding is feasible and exploitable as an alternative to surgical castration also for pigs slaughtered at heavy BW.

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 faecal soiling on skatole and androstenone occurrence in organic entire male pigs

Production of entire male pigs could be a future strategy for organic pig production. However, production of entire males leads to increased risk of carcasses with elevated boar taint levels. It is hypothesized that skatole levels in pig meat are affected by faecal soiling and that organic housing facilities can increase the risk of pigs being heavily soiled. Therefore, the overall aim of this study was to investigate if increased pig and pen soiling increases skatole concentration in entire male pigs. In five herds, 1174 organic entire male pigs were reared in four batches across two seasons, summer and winter. Measurements of pig and pen soiling, as well as fat skatole and androstenone concentration and human nose sensory tests of fat odour, were performed. Skatole and androstenone concentrations varied greatly within and between herds with a 10% and 90% percentile for the overall population of 0.02 and 2.25 µg/g for skatole and 0.53 and 4.84 µg/g for androstenone. Human nose positive tests averaged 18.3% with great variation between herds and seasons. Pen soiling had significant effects on pig soiling. Moreover, outdoor pen soiling significantly affected skatole concentration in interactions with herd and season (P<0.001 and P=0.003) and affected human nose positive risk in interaction with herd (P=0.005). Soiling on indoor pen areas did not affect skatole levels and no effect on androstenone was found for any pen area. Soiling of pigs affected both skatole and androstenone levels, with the size of the head and abdomen body areas covered in manure showing significant positive effects on skatole concentration. No effect of density of the manure layer was found on either boar taint measure. Herd significantly affected both skatole and androstenone in fat as well as the human nose positive risk. The human nose test revealed no effect from pig soiling. A large variation in the different boar taint measures was found for both high and low scores of pen and pig soiling, and only a small difference in skatole and androstenone concentrations between the high and low soiling categories was found. Therefore, while increasing the hygiene management could be a strategy for reducing boar taint in production of organic entire male pigs, it should be emphasized that other factors would also need to be considered.

Development of a quantitative method for the simultaneous analysis of the boar taint compounds androstenone, skatole and indole in porcine serum and plasma by means of ultra-high performance liquid chromatography coupled to high resolution mass spectrometry

Boar taint is an off-odour occurring while heating meat or fat from boars. A method detecting the three compounds (androstenone, skatole and indole) simultaneously in blood would offer substantial advantages since it would allow monitoring the impact of rearing strategies. Therefore, a UHPLC-HR-Orbitrap-MS analysis method is optimized and validated for the quantification of these compounds in plasma or serum. Sample pre-treatment involved an extraction with diethylether followed by a centrifugal filtration (30 kDa). Limits of detection and quantification varied between 0.5 and 1 μg L(-1) and 2 and 3 μg L(-1) for the three compounds, respectively. Besides, an excellent repeatability (RSD < 7.6%), within-laboratory reproducibility (RSD<10.5%), recovery (87-97%) and linearity (R(2)>0.99) were recorded. Correlations between serum/plasma and fat levels of the boar taint compounds were positive for skatole (r(serum) = 0.39 and r(plasma) = 0.84) and androstenone (r(serum) = 0.73-0.78 and r(plasma) = 0.32-0.80).

Measurement of boar taint in porcine fat using a high-throughput gas chromatography-mass spectrometry protocol

This work outlines an optimized gas chromatrography-mass spectrometry (GC-MS) based protocol for screening of the presence of the three boar-taint-producing compounds indole, skatole (3-methylindole), and androstenone (5α-androst-16-en-3-one) in porcine fat. The study shows that an accuracy suitable for sample screening can be achieved even when speed and ease of sample handling is prioritized and without the use of internal standards. The method provides levels of detection of 82 ng/g for indole, 97 ng/g for skatole, and 623 ng/g for androstenone (in a 2 g natural backfat matrix). A least-squares approach of predicting the sample analyte mass from instrument response is shown to have prediction errors (root-mean-square error) of 96 ng/g for indole, 94 ng/g for skatole, and 331.3 ng/g for androstenone. The method is intended for discrimination of samples in risk groups, and a scheme is proposed to turn the GC-MS response of the boar-taint analytes into risk classes.

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.

Development of an analytical approach for identification and quantification of 5-α-androst-16-en-3-one in human milk

A method was developed for the quantification of 5-α-androst-16-en-3-one in human breast milk based on application of a stable isotope dilution assay using 5α-androst-16-en-3-one-6, 6-d(2). The procedure includes extraction of the human milk by hexane with subsequent clean-up of the obtained extract by gel permeation and silica gel column chromatography. The extracted samples were analyzed by gas chromatography-mass spectrometry. Using this method 5-α-androst-16-en-3-one could be identified and for the first time quantified in a concentration range of 26-155 ng/kg in human milk.

Performances, meat quality and boar taint of castrates and entire male pigs fed a standard and a raw potato starch-enriched diet

In Europe there is increasing concern about the common practice of surgical castration of piglets without anaesthesia. One possible alternative to completely avoid castration is entire male pig production. Thus, the objective of the study was to compare the growth performance, carcass characteristics, organ weights, meat quality traits, fat score and boar taint compounds in the adipose tissue of group-penned entire male pigs and castrates. Furthermore, the effect of raw potato starch (RPS) fed for 7 days prior to slaughter was determined. Pigs (n = 36) were blocked by BW into 12 blocks (3 littermates/block) and assigned to three experimental groups: surgical castrates (C); entire males (EM); and entire males offered RPS (30 g RPS/100 g diet) for 7 days prior to slaughter (EM+). Pigs had ad libitum access to the feed from 22 to 107 kg, individual feed intake was recorded daily and BW once a week. Entire males grew slower (EM: 771, EM+: 776 v. C: 830 g/day; P < 0.01), consumed less feed (EM: 1.87, EM+: 1.89 v. C: 2.23 kg/day; P < 0.01) and were more efficient (feed conversion ratio: EM: 2.42, EM+: 2.44 v. C: 2.69 kg/kg; P < 0.01) than C. Compared to C, carcass dressing percentage was lower (EM: 79.4, EM+: 79.4 v. C: 81.6%; P < 0.01) and percentage of valuable cuts was higher (EM: 57.3, EM+: 56.5 v. 52.6%; P < 0.01) in entire males. The hearts (EM: 426, EM+: 425 v. C: 378 g), kidneys (EM: 387, EM+: 378 v. C: 311 g), bulbourethral (EM: 200, EM+: 195 v. C: 7 g) and salivary glands (EM: 99, EM+: 94 v. C: 42 g) were heavier (P < 0.001) in entire males than in C. Meat quality traits did not (P > 0.05) differ among experimental groups but the adipose tissue was more unsaturated in entire males than in C as indicated by the higher fat scores (EM: 69.1, EM+: 67.2 v. C: 63.6; P < 0.01). Feeding RPS reduced (P = 0.04) the skatole tissue concentrations (expressed in μg/g lipid) in EM+ (0.22) compared to EM (0.85), whereas androstenone and indole levels were not (P 0.60) affected (EM: 1.7 and 0.10, EM+: 2.0 and 0.09, respectively). Although the current results confirmed the high efficiency of entire males compared to castrates, the observed high androstenone levels represent a major challenge to implement entire males production.

The effect of cereal type and enzyme supplementation on carcass characteristics, volatile fatty acids and intestinal microflora and boar taint in entire male pigs

A 2 × 2 factorial experiment was conducted to investigate the effects of cereal type (barley v. oat) and exogenous enzyme supplementation (with or without) on intestinal fermentation, and on indole and skatole levels in the intestinal content and the adipose tissue in finisher boars. The experimental treatments were as follows: (i) barley-based diet, (ii) barley-based diet with enzyme supplement, (iii) oat-based diet and (iv) oat-based diet with enzyme supplement. The enzyme supplement contained endo-1,3(4)-β-glucanase (EC 3.2.1.6) and endo-1,4-β-xylanase (EC 3.2.1.8). The animals were fed ad libitum for 45 days from 76.0 to 113.6 kg live weight. Feeding barley-based diets led to higher (P < 0.05) total volatile fatty acids concentrations in the large intestine. Proportions of propionic- and butyric-acids were higher and that of acetic acid lower in digesta from barley-based in comparison to oat-based diets (P < 0.001). Consequently, pH in the large intestine was higher after feeding oat-based in comparison to barley-based diets. Animals fed unsupplemented oat-based diet had higher (P < 0.01) indole concentrations in the digesta from the proximal colon than those fed barley-based diets. Feeding oat-based diets led to lower (P < 0.01) skatole and higher (P < 0.001) indole concentrations in the digesta from the terminal colon than barley-based diets. skatole concentrations in the adipose tissue did not differ (P > 0.05) between the experimental treatments. Pigs offered the barley-based diets had lower (P < 0.001) indole concentrations in the adipose tissue compared with those fed the oat-based diet. In conclusion, barley-based diets were more efficient than oat-based diets in limiting concentrations of indole in the adipose tissue.

Temporal aspects related to the perception of skatole and androstenone, the major boar odour compounds

Pork fat samples from 50 boars slaughtered at a commercial abattoir were analysed for skatole and androstenone concentrations and grouped within a 3×3 matrix representing low, medium and high levels of the odour compounds. A 10 member sensory panel, screened and trained to recognise and quantify skatole and androstenone odour intensities, was used to verify the human perception of boar odour in these pork fat samples immediately after heating (±65°C) and following a cooling period of ten minutes (±25°C). Principal component analysis revealed that the sensory panel differentiated the pork fat samples first and foremost on the basis of the presence or absence of androstenone and/or skatole odours and secondly on the character of the androstenone or skatole odour. Evidence of adaptation towards the odour of skatole was shown by a decreased sensitivity over replicates. Sensory perception of boar odour seems to have a temporal character which can be explained by differences in volatilisation (involving both odourant release and retention) of skatole and androstenone, odour synergism and possibly differences in the properties of the fat matrix of different samples. The results suggest that factors influencing volatilisation of skatole and androstenone should also be considered when predicting sensory responses of boar odour.

Feeding Jerusalem artichoke reduced skatole level and changed intestinal microbiota in the gut of entire male pigs

Different levels of dried Jerusalem artichoke were fed to entire male pigs 1 week before slaughter. The objective was to investigate the effect on skatole level in the hindgut and in adipose tissue, as well as the effect on microflora and short-chain fatty acids (SCFA) in the hindgut. Five experimental groups (n = 11) were given different dietary treatments 7 days before slaughtering: negative control (basal diet), positive control (basal diet + 9% chicory-inulin), basal diet + 4.1% Jerusalem artichoke, basal diet + 8.1% Jerusalem artichoke and basal diet + 12.2% Jerusalem artichoke. Samples from colon, rectum, faeces and adipose tissue were collected. Effect of dietary treatment on skatole, indole and androstenone levels in adipose tissue and on skatole, indole, pH, dry matter (DM), microbiota and SCFA in the hindgut was evaluated. Feeding increasing levels of Jerusalem artichoke to entire male pigs reduced skatole in digesta from colon and in faeces (linear, P < 0.01). There was also a tendency towards a decreased level of skatole in adipose tissue (linear, P = 0.06). Feeding Jerusalem artichoke decreased DM content in colon and faeces and pH in colon (linear, P < 0.01). Increasing levels of Jerusalem artichoke resulted in a reduced level of Clostridium perfringens in both colon and rectum (linear, P < 0.05) and a tendency towards decreased levels of enterobacteria in colon (linear, P = 0.05). Further, there was an increase in total amount of SCFA (linear, P < 0.05), acetic acid (linear, P < 0.05) and valerianic acid (linear, P < 0.01) in faeces. In conclusion, adding dried Jerusalem artichoke to diets for entire male pigs 1 week before slaughter resulted in a dose-dependent decrease in skatole levels in the hindgut and adipose tissue. The reduced skatole levels might be related to the decrease in C. perfringens and the increase in SCFA with subsequent reduction in pH.

Effect of feed restriction on hormones, performance, carcass traits, and meat quality in immunocastrated pigs

The aim of this study was to assess the effect of feed restriction applied to immunocastrated pigs in the period after the second vaccination (V2) against GnRH on hormonal status, performance, carcass traits, and meat quality. Immunocastrated pigs (IC) were compared with entire males (EM) and surgical castrates fed ad libitum. Pigs (Large White × Landrace) × Pietrain were either left entire or surgically castrated within 1 wk after birth (SC, n = 22). At 83 d of age, the entire males were further allotted to treatment groups (individual housing) of ad libitum fed EM (n = 24), ad libitum fed IC (IC-L, n = 21), or restrictively fed IC (IC-R, n = 21). At that time, the first vaccination (V1) was applied to IC-L and IC-R pigs. One week after V2 (age 130 d), feed restriction (≈ 80% of the ad libitum feed intake of SC pigs) was applied to IC-R pigs. The experiment ended 5 wk after V2, when pigs were 165 d old. Immunocastration successfully reduced boar taint compounds and size of reproductive organs. At 130 d, serum leptin concentrations were similar in all groups, whereas IGF-I concentration was less in SC (P ≤ 0.002) than in the other groups. Three weeks after V2, leptin concentrations of both IC groups were in between EM (least) and SC (greatest). The reverse was observed for IGF-I. Feed restriction had no effect on leptin or IGF-I concentrations in IC pigs. In the period V1 to V2, performance differed mainly between EM and SC, whereas both IC groups had feed intake and feed conversion ratio similar to EM and intermediate daily BW gain, not differing from either EM or SC. After V2, IC-L pigs increased their feed intake to the concentrations of SC, with faster growth compared with the other 3 groups (P < 0.05) and fatter carcasses compared with EM pigs (P = 0.007). Similar performance and carcass leanness were observed for IC-R and EM pigs. During preslaughter handling more carcass lesions were noted in EM and IC-R than in IC-L or SC pigs (P < 0.002). Neither immunocastration nor feed restriction had any effect on meat quality, but EM had greater drip loss, less intramuscular fat, and decreased tenderness than SC pigs. In conclusion, restricting feed intake can increase production efficiency but also aggressiveness of IC pigs.

Inter-laboratory comparison of methods to measure androstenone in pork fat

Today, different analytical methods are used by different laboratories to quantify androstenone in fat tissue. This study shows the comparison of methods used routinely in different laboratories for androstenone quantification: Time-resolved fluoroimmunoassay in Norwegian School of Veterinary Science (NSVS; Norway), gas chromatography coupled to mass spectrometry in Co-operative Central Laboratory (CCL; The Netherlands) and in Institut de Recerca i Tecnologia Agroalimentàries (IRTA; Spain), and high-pressure liquid chromatography in Agroscope Liebefeld-Posieux Research Station (ALP; Switzerland). In a first trial, a set of adipose tissue (AT) samples from 53 entire males was sent to CCL, IRTA and NSVS for determination of androstenone concentration. The average androstenone concentration (s.d.) was 2.47 (2.10) μg/g at NSVS, 1.31 (0.98) μg/g at CCL and 0.62 (0.52) μg/g at IRTA. Despite the large differences in absolute values, inter-laboratory correlations were high, ranging from 0.82 to 0.92. A closer look showed differences in the preparation step. Indeed, different matrices were used for the analysis: pure fat at NSVS, melted fat at CCL and AT at IRTA. A second trial was organised in order to circumvent the differences in sample preparation. Back fat samples from 10 entire males were lyophilised at the ALP labortary in Switzerland and were sent to the other laboratories for androstenone concentration measurement. The average concentration (s.d.) of androstenone in the freeze-dried AT samples was 0.87 (0.52), 1.03 (0.55), 0.84 (0.46) and 0.99 (0.67) μg/g at NSVS, CCL, IRTA and ALP, respectively, and the pairwise correlations between laboratories ranged from 0.92 to 0.97. Thus, this study shows the influence of the different sample preparation protocols, leading to major differences in the results, although still allowing high inter-laboratory correlations. The results further highlight the need for method standardisation and inter-laboratory ring tests for the determination of androstenone. This standardisation is especially relevant when deriving thresholds of consumer acceptance, whereas the ranking of animals for breeding purposes will be less affected due to the high correlations between methods.

Review of analytical methods to measure boar taint compounds in porcine adipose tissue: the need for harmonised methods

This comprehensive review describes the analytical methods developed for quantification of the boar taint compounds skatole and androstenone in porcine adipose tissue. The following parts are considered; sampling, sample preparation, calibration and instrumentation. Additionally, method performance characteristics and level of validation of the existing methodology are discussed. It is concluded that there is a need for further validation of existing methods and need for standardisation of methodology to quantify boar taint compounds. Facing a possible near future ban of castration of male piglets would enforce further method harmonisation in this field.

Prevalence and relationships of sensory taint, 5α-androstenone and skatole in fat and lean tissue from the loin (Longissimus dorsi) of barrows, gilts, sows, and boars from selected abattoirs in the United States

This study assessed prevalence of boar taint in backfat and lean of barrows, gilts, sows, and boars, collected from abattoirs, without knowledge of the farms of origin, in different regions in the United States. Concentrations of 5α-androstenone (liquid chromatography/mass spectroscopy) and skatole (liquid chromatography with fluorescent detection) in backfat were measured. A trained panel evaluated boar taint aroma in heated samples. Mean 5α-androstenone and skatole levels were low among barrows, gilts, and sows, whereas 55.8% of boars scored above a 1.0 μg/g threshold for 5α-androstenone concentrations and 34.2% were above a 0.2 μg/g threshold for skatole concentrations. Mean aroma scores for backfat and lean from barrows, gilts, and sows were low. In comparison, 59.2% of boars had elevated mean aroma scores from fat samples and 31.7% from lean. Importantly, boar taint aroma was detectable by the trained panel in at least some animals in each of the sex classes.