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.     

Biochemical, nutritional and genetic effects on boar taint in entire male pigs

Pork odour is to a great extent affected by the presence of malodorous compounds, mainly androstenone and skatole. The present review outlines the current state of knowledge about factors involved in the regulation of androstenone and skatole in entire male pigs. Androstenone is a pheromonal steroid synthesised in the testes and metabolised in the liver. Part of androstenone accumulates in adipose tissue causing a urine-like odour. Skatole is produced in the large intestine by bacterial degradation of tryptophan and metabolised by hepatic cytochrome P450 enzymes and sulphotransferase. The un-metabolised part accumulates in adipose tissue, causing faecal-like odour. Androstenone levels are mostly determined by genetic factors and stage of puberty, whereas skatole levels in addition to genetic background and hormonal status of the pigs are also controlled by nutritional and environmental factors. To reduce the risk of tainted carcasses entering the market, male pigs are surgically castrated in many countries. However, entire males compared to castrates have superior production characteristics: higher growth rate, better feed efficiency and leaner carcasses. Additionally, animal welfare aspects are currently of particular importance in light of increasing consumers' concerns. Nutrition, hormonal status, genetic influence on boar taint compounds and the methods to develop genetic markers are discussed. Boar taint due to high levels of skatole and androstenone is moderately heritable and not all market weight entire males have boar taint; it should thus be possible to select for pigs that do not have boar taint. In these studies, it is critical to assess the steroidogenic potential of the pigs in order to separate late-maturing pigs from those with a low genetic potential for boar taint. A number of candidate genes for boar taint have been identified and work is continuing to develop genetic markers for low boar taint. More research is needed to clarify the factors involved in the development of boar taint and to develop additional methods to prevent the accumulation of high concentrations of skatole and androstenone in fat. This review proposes those areas requiring further research.     

Weight and season affects androstenone and skatole occurrence in entire male pigs in organic pig production

To investigate the extent to which the level of androstenone and skatole decreases with a decrease in live weight and/or age at slaughter of entire male pigs produced under organic standards, 1174 entire male pigs were raised in parallel in five organic herds, distributed across four batches in summer and winter. The median androstenone level was high for organic entire male pigs (1.9 µg/g), but varied greatly both within and between herds. Median skatole level was 0.05 µg/g, also with a wide range both within and between herds. Decreasing live weight over the range of 110±15.6 kg s.d. was found to decrease androstenone as well as skatole concentration, however, with different patterns of association. Age did not have significant direct effect on either androstenone or skatole levels. Androstenone levels were higher during winter than summer (P<0.0001), but no difference in skatole was found between seasons. The study concludes that decreasing live weight at slaughter could be an applicable management tool to reduce risk of boar taint and the level of tainted carcasses for a future production of entire male pigs within the organic pig production system, although further studies are needed as great variation in boar taint was found also for low weight animals.     

Long-term effect of vaccination against gonadotropin-releasing hormone, using Improvac, on hormonal profile and behaviour of male pigs

The objective of this study was to evaluate the long-term effect of a gonadotropin-releasing hormone (GnRH) vaccine, Improvac (Pfizer Ltd.), on the levels of GnRH antibodies, testosterone, estrone sulphate (E1S) and androstenone, as well as skatole and indole in male pigs. Additionally, the long-term effect of immunocastration on social and sexual behaviour was studied. Male pigs were assigned to two treatment groups: a treatment group given two doses of Improvac (n=12) and a control group of entire male pigs (n=12). The pigs were kept either 16 or 22 weeks after vaccination. Blood samples were collected five or six times; prior to both first and second vaccination, then three or four times during the 16 or 22 week period after second vaccination. Immunocastration significantly reduced levels of testosterone and E1S in plasma, and levels of androstenone in fat (P<0.001 for all). Skatole and indole levels in plasma and fat were also lower in immunocastrated pigs than in entire male pigs. These effects lasted up to 22 weeks after the second vaccination. Testis weight and bulbourethral gland length were lower in immunocastrated pigs at slaughter and these pigs showed less social, manipulating and aggressive behaviour than entire male pigs. The immunocastrated pigs remained sexually inactive throughout the study. Our study represents a further step in the evaluation of the effectiveness of Improvac as an alternative to surgical castration of entire male pigs. It shows that Improvac may have an extended effect compared with that currently implied by the directions for use.     

Effect of polymorphism in the porcine cytochrome b5 ( CYB5A) gene on androstenone and skatole concentrations and sexual development in Swedish pig populations

The present study investigated the presence of a single-nucleotide polymorphism (G > T) at base -8 upstream of ATG in 5' untranslated region of cytochrome b5 (CYB5A) gene in Swedish pig populations and evaluated the significance of this polymorphism for androstenone and skatole levels, sexual development and performance parameters in pigs. Frequencies of the T allele were 6.7% for Swedish Yorkshire × Landrace crossbred pigs (n = 245), 6.5% for Swedish Yorkshire (n = 99) and 12.8% for Landrace breed (n = 74). No deviations from Hardy-Weinberg equilibrium were observed in the investigated populations. In Swedish Yorkshire × Landrace crossbred entire male pigs (n = 193), plasma samples were analysed for skatole, androstenone, testosterone and oestrone sulphate, and fat samples were analysed for androstenone, skatole and free oestrone. Additionally, testis weight and bulbourethral gland length for crossbred pigs were recorded. Plasma androstenone levels were significantly lower in the G/T genotype at 90 kg live weight compared with the wild G/G genotype at the same live weight (P = 0.006). In heavier pigs, plasma androstenone levels did not differ between genotypes (P = 0.382). Fat androstenone levels were not affected by CYB5A genotype (P = 0.252). Skatole levels in the G/T genotype at 115 kg live weight were lower compared with those in the G/G genotype in plasma (P = 0.048) and fat (P = 0.028), although no differences were observed in lighter pigs. Testis weight, bulbourethral gland length, testosterone and oestrone sulphate levels in plasma, and oestrone levels in fat were not affected by genotype. We concluded that the presence of the T allele in the CYB5A gene resulted in lower androstenone levels in plasma, and lower skatole levels in fat and plasma; this reduction, however, was dependent on the live weight of the animals. Reproductive hormones and growth rate did not differ between the pigs of different genotypes, whereas a higher lean meat content was found in the G/T genotype in comparison with the G/G genotype. The practical application of those results in Sweden is doubtful because of lack of the effect on androstenone in fat and the low frequency of the T allele in the studied Swedish pig populations.     

Modulation of porcine cytochrome P450 enzyme activities by surgical castration and immunocastration

The present study aimed to evaluate some cytochrome P450 metabolic enzyme activities in hepatic microsomes prepared from entire male pigs (uncastrated pigs), surgically castrated pigs and pigs immunized against gonadotropin-releasing hormone (immunocastrated pigs). The activities of the following enzymes were measured: ethoxyresorufin O-deethylase (EROD, CYP1A1/1A2), methoxyresorufin O-deethylase (MROD, CYP1A2), pentoxyresorufin O-depentylase (PROD, CYP2B), coumarin hydroxylase (COH, CYP2A) and p-nitrophenol hydroxylase (PNPH, CYP2A/2E1). The total cytochrome P450 contents were not affected by either surgical or immunocastration. Hepatic microsomal activities for EROD, PROD, COH and PNPH were lower in entire male pigs compared with surgically castrated and immunocastrated pigs (P < 0.05). Surgically and immunocastrated male pigs were similar with respect to EROD, MROD, PROD and COH activities (P > 0.05), whereas surgically castrated pigs exhibited lower PNPH activity compared with immunocastrated pigs (P = 0.029). The effect of different concentrations of testicular steroids - testosterone, 17β-estradiol, free estrone and androstenone - on enzyme activities was evaluated by in vitro microsomal study. Testosterone at the concentration of 8 pmol/ml inhibited EROD activities and estradiol-17β at the concentration of 1.8 pmol/ml inhibited PROD activities in hepatic microsomes from surgically castrated pigs. The highest concentration of androstenone (7520 pmol/ml) inhibited COH activities, whereas a 42-fold lower concentration of androstenone (180 pmol/ml) stimulated COH activities in surgically castrated pigs. Both free estrone (3.5 pmol/ml) and androstenone (55 pmol/ml) inhibited EROD activities in microsomes from entire male pigs. Stimulation of COH activities by the highest dose of free estrone (18 pmol/ml) was recorded in microsomes from entire male pigs. However, these effects of steroids were not concentration-dependent and the maximum extent did not exceed ±15% variation compared with the controls. There was no inhibition of PNPH activities in the hepatic microsomes from either entire or castrated pigs. In conclusion, we showed that EROD, PROD, COH and PNPH activities were lower in entire male pigs compared with those in surgically and immunocastrated pigs. Direct inhibition by the testicular steroids - testosterone, 17β-estradiol, free estrone and androstenone - was not the primary cause of the reduced enzyme activities.     

A novel polymorphism in the 5′ untranslated region of theporcine cytochrome b5 (CYB5) gene is associated with decreased fat androstenone level

Raising intact male pigs would have a significant economic impact on the pork industry; however, the presence of 16-androstene (a major cause of boar taint) in meat from male pigs would be highly objectionable to consumers. In pigs, a positive correlation has been found between cytochrome b5 (CYB5) and production of 16-androstene. The search for polymorphism of CYB5 and functional analysis of polymorphism found should have an important impact on the efforts to develop genetic markers to select for low androstenone levels in fat from pigs. The aim of this study was to search the porcine CYB5 gene for mutations, examine its expression, identify genetic polymorphisms, and study how a genetic variation in this enzyme translates into interindividual variation in androstenone levels in fat from pig testis. We have identified a single nucleotide polymorphism (SNP) (G→T) at base 8 upstream of ATG in the CYB5 5′ untranslated region which is associated with a lower fat androstenone level. Of the 229 testis samples tested, 84.8% were homozygous for the variant G, 12.4% were heterozygous, and 2.8% were homozygous for the variant T. Functional analysis of this mutation revealed that an individual homozygous for the T allele showed significantly lower CYB5 activity than an individual homozygous for the G allele. Thus, this may be at least partially responsible for a lower level of androstenone in pigs. Our findings provide an important genetic basis toward the goal of predicting the androstenone status in pigs and developing genetic markers for low androstenone.     

Active immunization against gonadotrophin-releasing hormone in Chinese male pigs: effects of dose on antibody titer, hormone levels and sexual development

The objective of this study was to determine the optimal dose of a GnRH vaccine for immunocastration of Chinese male pigs, based on immune, endocrine and testicular responses. Forty-two crossbred (Chinese Yanan x Large White) male pigs were randomly assigned to one of the five treatments as follows: (I) 0 microg (control, n=8); (II) 10 microg (n=8); (III) 62.5 microg (n=8); (IV) 125 microg (n=8); (V) 250 microg (n=10), D-Lys6-GnRH tandem dimer (TDK) peptide equivalent of conjugate (TDK-OVA), using Specol as the adjuvant. Pigs were immunized at 13 and 21 weeks of age and were slaughtered at 31 weeks of age. Blood samples for antibody titer and hormone assays were collected at 13, 21, 24 and 31 weeks of age. At these time-points, testis size was also measured. At slaughter, testis weight was recorded and fat samples were collected for androstenone assay. Four animals, one out of each immunized group, responded poorly to the immunization (non-responders). At slaughter, serum testosterone and LH levels, fat androstenone levels and testis size/weight of these non-responders were similar to those in control animals. Antibody titers of non-responders were substantially lower (P<0.05) than in other immunized pigs. For the animals that responded well to the immunization (immunocastrated pigs), serum testosterone and LH levels, fat androstenone levels and testis size or weight were reduced (P<0.05) as compared to either controls or non-responders, at all doses tested. There was a significant effect of dose of TDK-OVA on antibody titers. The overall mean antibody titers in the 62.5 or 125 microg dose group (53.6 and 50.5% binding, respectively) were significantly higher than in the 10 or 250 microg group (39.2 and 40.24% binding, respectively). At slaughter, there was a significant dose effect on testis size or weight and on serum testosterone levels, but there was no dose effect on serum LH levels and fat androstenone levels. Testis size or weight in the 10 microg group was reduced to a lesser extent (P<0.05) than in the three higher dose groups. At slaughter, in comparison to controls, mean testis size of immunocastrated pigs in treatments II-V was reduced to 55, 21, 33 and 25%, respectively, whereas testis weight was reduced to 39, 12, 18 and 14%, respectively. Reduction of testis size and/or weight is important for visual assessment of castration at the slaughterline, therefore, it is concluded that a dose of 10 microg peptide is not suitable. We conclude that, within the dose-range studied, the 62.5 microg dose is optimal for future GnRH immunization studies or future practical use in immunocastration of Chinese male pigs.     

Age at castration (surgical or immunological) impacts carcass characteristics and meat quality of male pigs

In order to accurately estimate body composition at slaughter and to meet specific market targets, the influence of age at time of castration (surgical or immunological) on body composition and boar taint indicators must be determined for male pigs. In all, 48 males were randomly assigned to one of four management regimens: (1) entire male pigs (EM), (2) EM surgically castrated at ~40 kg BW and 10 weeks of age (late castrates; LC), (3) conventional, early surgical castrates (within 4 days of birth; EC) and (4) EM immunized with a gonadotropin-releasing hormone (GnRH) analog (primary dose at 30 kg BW and 8 weeks of age; booster dose at 70 kg and 14 weeks of age; IM). Pigs were fed corn and soybean meal-based diets that were not limiting in essential nutrients. Back fat was sampled on days −3, 8, 18 and 42, relative to administering the booster dose of GnRH analog at day 0, to determine androstenone concentrations (n=8 or 9/group). Fat androstenone concentrations in IM were lower than EM between days 8 and 42 after administering the booster dose (173 v. 863 ng/g, respectively; P<0.01), and were not different from surgically castrated males (EC and LC) after day 18. Slaughter occurred at ~115 kg BW, 42 days (6 weeks) after administering the booster dose for IM, and 10 and 20 weeks after surgical castration for LC and EC, respectively (n=8 or 9/group). At slaughter, live BW, liver weight as a percent of live BW, dissectible bone as a percent of cold carcass side, body protein and water contents and whole-body protein deposition decreased with time after surgical castration (linear; P<0.05), whereas dressing percentage, dissectible fat, probe fat depth and body fat content increased with time after surgical castration (linear; P<0.05). The IM had intermediate dressing percentage and dissected fat to EM and EC, whereas liver weight as a percent of live BW and body protein and lipid contents were not different from EM. Whole-body lipid deposition tended to be greater in IM than in EM between 14 and 20 weeks of age (373 v. 286 g/d; P=0.051). In conclusion, castration of male pigs after 6 weeks of age has a lasting effect on physical and chemical body composition. The relationship between time after castration and body composition may be developed to predict carcass composition and can be used to determine the ideal immunization schedule aimed at specific markets in the future.     

On-farm prevalence of and potential risk factors for boar taint

Boar taint is an unpleasant taste and odor that can occur in entire male pigs and is caused by androstenone, skatole, and to a lesser extent indole accumulating in fat tissue. In the present observational study, we evaluated an extensive list of such potential risk factors which influence boar taint: social hierarchy and puberty attainment, housing, health, preslaughter conditions, season, feed, carcass composition, slaughter weight or age, and breed. Details on these factors were collected by interviews with the participating farmers, observations on each farm by trained observers and farmers, as well as slaughterhouse data. Twenty-two farms (in West- and East-Flanders, ranging from 160 to 600 sows, selected on suitability) raising entire male pigs were included in the study to evaluate the link between boar taint and potential risk factors related to the farm and slaughter batch (114 slaughter batches and 16 791 entire male pigs in total). Average olfactory boar taint prevalence was 1.8 ± 0.8%. Boar taint prevalence varied also within farms up to a maximum range between slaughter batches of 9.1% which suggests an effect of factors varying between slaughter batches such as season or other variables varying between slaughter batches. Less aggressive behavior at the end of fattening as well as lower skin lesion scores at fattening as well as at slaughter could be associated with less boar taint. The same might be said for sexual behavior, though less convincingly from this study. Measures that reduce aggression and stress have therefore have the potential to lower boar taint prevalence. The same might be said for sexual behavior, though less convincingly from this study. Furthermore, boar taint prevalence was generally higher in winter than in summer, which is relevant from a planning perspective for the slaughterhouses to seek alternative markets. Finally, increased CP gave significantly lower boar taint prevalences. This may to some extent be explained by the negative association between boar taint and lean meat percentage, as increased dietary CP levels promote the carcass lean meat percentages which can then be associated with lower boar taint levels.     

Differences in testosterone, androstenone, and skatole levels in plasma and fat between pubertal purebred Duroc and Landrace boars in response to human chorionic gonadotrophin stimulation

The concentrations of the boar taint compounds androstenone and skatole in plasma and fat, together with those of testosterone in plasma, were investigated in pubertal purebred Duroc and Landrace boars following stimulation with human chorionic gonadotrophin (hCG). Higher initial levels of androstenone and testosterone were found in Duroc than Landrace boars. Duroc boars, which were approximately ten days older than the Landrace boars, also showed a more advanced stage of spermatogenesis than Landrace boars. While Landrace boars had the highest skatole levels. Following stimulation with hCG the relative increases in testosterone, androstenone, and skatole concentrations were highest in Landrace boars. The level of androstenone in fat three days after hCG stimulation exceeded 1 μg/g fat in all stimulated boars. The decreases in plasma levels of androstenone and testosterone on Days 2 and 3 after hCG stimulation were more pronounced in Landrace than Duroc boars. However, unlike the plasma androstenone and testosterone levels, the plasma concentrations of skatole did not decrease on Days 2 and 3 following stimulation, but remained elevated on Day 3. These results indicate that the lower levels of testicular steroids in Landrace boars compared with Duroc boars was not due to a lower production capacity, but more likely to a faster dissapearance of steroids in Landrace boars. In the present study, age, live weight, and testicular development did not significantly contribute to the variation in fat androstenone. The present data and previous reports on candidate genes related to androstenone biosynthesis and metabolism suggests that future selection against factors associated with boar taint remains a possible solution for the problem of boar taint in the swine industry.     

Feeding dried chicory root to pigs decrease androstenone accumulation in fat by increasing hepatic 3β hydroxysteroid dehydrogenase expression

The present study investigated the in vivo effect of chicory root on testicular steroid concentrations and androstenone metabolizing enzymes in entire male pigs. Furthermore, the effect on skatole and indole concentrations in plasma and adipose tissue was investigated. The pigs were divided into two groups; one receiving experimental feed containing 10% dried chicory root for 16 days before slaughter, the control group was fed a standard diet. Plasma, adipose and liver tissue samples were collected at slaughter. Plasma was analyzed for the concentration of testosterone, estradiol, insulin-like growth factor 1 (IGF-1), skatole and indole. Adipose tissue was analyzed for the concentration of androstenone, skatole and indole, while the liver tissue was analyzed for mRNA and protein expressions of 3β-hydroxysteroid dehydrogenase (3β-HSD), sulfotransferase 2A1 and heat-shock protein 70 (HSP70). The results showed that the androstenone concentrations in the adipose tissue of chicory fed pigs were significantly (p<0.05) lower and indole concentrations were higher (p<0.05) compared to control fed pigs. Moreover the chicory root fed pigs had increased mRNA and protein expression of 3β-HSD and decreased HSP70 expression (p<0.05). Testosterone and IGF-1 concentrations in plasma as well as skatole concentrations in adipose tissue were not altered by dietary intake of chicory root. It is concluded that chicory root in the diet reduces the concentration of androstenone in adipose tissue via induction of 3β-HSD, and that these changes were not due to increased cellular stress.     

Genetic determinism of boar taint and relationship with growth traits,meat quality and lesions

Breeding entire males is an alternative to surgical castration to improve their welfare. However, entire males may have a major quality defect called boar taint. Boar taint is partly due to the presence of androstenone in fat. In this study, we estimated the genetic parameters between androstenone and production traits to evaluate the consequences of selection against boar taint for traits of interest. We focused on growth traits, meat quality, lesions, hormone levels and computerised tomography measurements in purebred Piétrain (P) or Piétrain cross Large White (X) entire males. The number of measured animals varied from 670 P and 734 X for hormones concentrations to 553 P and 645 X for computerised tomography measurements. Skin lesions were measured on live pigs shortly after mixing, at the end of the fattening period, and on carcasses. Heritabilities of traits measured by tomography ranged from low to high: femur density (P: 0.34, X: 0.69), loin eye area (P: 0.53, X: 0.88) and loin eye density (P: 0.12, X: 0.18). The mean number of lesions at each stage was lower in purebred pigs than in crossbreds (entering the fattening stage 4.01 in P and 4.68 in X; before slaughter 3.72 in P and 4.22 in X; on carcass 4.50 in P and 4.96 in X). We also observed a decrease in the average number of lesions between the two stages in live pigs. We found high genetic correlations between stages in purebred pigs (0.74 to 0.76) but low correlations (−0.30 to 0.29) in crossbred pigs. Selection aiming to decrease fat androstenone is feasible (h² = 0.57 in P and h² = 0.71 in X). It would have overall positive effects on meat production and quality traits. Selection aiming to reduce plasma oestradiol would strongly reduce the level of fat androstenone (rg = 0.89 in P and rg = 0.84 in X). Selection against oestradiol is easier and less invasive since it would only require a blood sample rather than a fat biopsy in live animals.     

Relationship between carcass weight, adipose tissue androstenone level and expression of the hepatic 3β-hydroxysteroid dehydrogenase in entire commercial pigs

Boar taint is a major meat-quality defect in pigs and is due to excessive accumulation of skatole and androstenone in adipose tissue. The present work investigated the relationship between carcass weight, levels of skatole and androstenone in adipose tissue, and expression of the hepatic androstenone-metabolising enzyme 3β-hydroxysteroid dehydrogenase (3β-HSD), in 22 entire male and 22 entire female crossbred pigs (Large White (40%) × Landrace (40%) × Duroc (20%)). Animals of each gender were divided into two subgroups (11 pigs in each subgroup): (i) conventional weight (carcass weight 59 to 77 kg) and (ii) heavy weight (carcass weight 84 to 95 kg). No relationship between carcass weight and adipose tissue skatole level was found for entire male pigs (r2 = 0.013, P > 0.05). There was a significant negative relationship between carcass weight and expression of the hepatic 3β-HSD protein (r2 = 0.502, P < 0.001) and a significant negative relationship between 3β-HSD protein expression and androstenone level in adipose tissue (r2 = 0.24, P < 0.05) in entire males. No relationship was found between carcass weight and 3β-HSD protein expression in female pigs (r2 = 0.001, P > 0.05). 3β-HSD expression was 59% higher in conventional-weight male pigs when compared with heavy-weight animals (P < 0.05) and 36% higher in heavy-weight females when compared with heavy-weight males (P < 0.05). It is concluded that an increase in slaughter weight of entire commercial crossbred Large White pigs is accompanied by inhibition of expression of the hepatic 3β-HSD protein, which might result in a reduced rate of hepatic androstenone clearance with its subsequent accumulation in adipose tissue. It is suggested that regulation of pig hepatic 3β-HSD expression is under the control of sex hormones.     

Influence of housing and season on pubertal development,boar taint compounds and skin lesions of male pigs

Rearing entire pigs may lead to meat quality and welfare problems in relation to pubertal development. A better knowledge of the sources of variation of pubertal development, behaviour and boar taint is needed before generalizing entire male pigs. From 84 days of age, entire male pigs were reared in groups of 10 either in a conventional (C, 1 m²/animal, slatted floor) or an enriched (E, 2.5 m²/animal, straw bedding, outdoor run) housing during spring or autumn and fed ad libitum (n=10/housing/season). Mounting behaviour was observed for 3 h during the third (M3), fourth (M4) and fifth (M5) months of age. The total number of skin lesions was counted on both sides of the pigs 1 day before the behavioural recordings. The time spent in the outdoor run was also recorded during 3 days per month. The animals were slaughtered at 161±1 days of age (122±9 kg live weight). Blood samples were collected at 89 (M3), 119 (M4) and 152 (M5) days of age and at slaughter for the testosterone and oestradiol measurements. The testes were collected at slaughter, freed from the surrounding tissues and weighed. The fat samples were collected for the androstenone and skatole concentration measurement. Plasma testosterone and oestradiol-17β (oestradiol), fat androstenone and skatole and weight of the testes did not differ between the housing systems. Plasma testosterone (8.3 v. 3.9 nmol/l, P<0.05) and oestradiol (12.0 v. 9.2 pmol/l, P<0.1) at M3, fat skatole (0.124 v. 0.043, P<0.03) and weight of the testes (587 v. 512 g, P<0.05) were higher in the autumn than in the spring trial, suggesting that the pubertal development was accelerated. The number of received mounting behaviours was slightly higher in the autumn (P=0.08) trial and was markedly higher in the E than in the C environment (P<0.003). Skin lesions were more numerous in the C than in the E housing at M4 and M5 and in the spring than in the autumn trial at M3 and M4 (P<0.05). Fat androstenone and the number of performed mounting behaviours were significantly correlated between each other and with numerous indicators of the pubertal development (P<0.05). The number of skin lesions was correlated with plasma testosterone and live weight (P<0.05). Overall, this study suggests the effect of season on sexual development, the effect of the housing system on behaviour, and demonstrates the links between sexual hormones, behaviour and boar taint.     

Estimation of genetic parameters of boar taint; skatole and androstenone and their correlations with sexual maturation

Boar taint is mainly caused by two components; skatole (3-methylindole) and androstenone. By castrating the male pigs, boar taint will be avoided. In Norway, castration of pigs will no longer be permitted after 2009. This represents a substantial cost for the Norwegian swine production. Other Norwegian studies have shown that a large proportion of pigs are above the consumer detection limits for these two chemical components. The obvious question for the geneticist arises: Is it possible to select against skatole and androstenone in a breeding programme? Skatole is produced in the gut by bacteria. It is then absorbed in the blood stream. Skatole is either metabolised in the liver or transported and stored in fatty tissue. Androstenone is produced in the testis, and its biochemical pathway is related to the pathway of testosterone. In this study, fatty tissue was collected from the carcasses of Norwegian Landrace and Duroc boars, and analysed for androstenone and skatole. The length of glandula bulbourethralis was measured on the same animals, as this is regarded as a good indicator of sexual maturation. Heritabilities of androstenone and skatole were substantial. The two components were genetically correlated. Sexual maturation was also highly heritable. However, correlations to both androstenone and skatole were significantly unfavourable.     

Pig meat quality from entire males

This paper constitutes an updated review of the production and meat quality aspects of rearing entire male pigs. Since a major obstacle in rearing entire males is the incidence of boar taint, possible methods for detection are also summarised. Safe and fast methods for detection of boar taint would be valuable in avoiding complaints from consumers. Pig meat quality is determined by many aspects, among which odour and taste are the most important attributes. Odour may be negatively affected by the presence of a pheromonal steroid, androstenone, and a fermentation product of l-tryptophan, skatole. Male pigs are surgically castrated in many countries to minimise the risk of accumulation of high levels of androstenone and skatole. Raising entire male pigs is more profitable because they have superior production characteristics and improved meat quality due to leaner carcasses and higher protein content, as compared to castrated pigs. Furthermore, surgical castration is negative from an animal welfare point of view. In most studies, no differences in sensory quality have been found between lean meat from entire male pigs with low levels of androstenone and skatole and pork from castrates and females. The question that remains is: which substances are responsible for boar taint besides androstenone and skatole and whether they need to be considered? The threshold values used for androstenone and skatole might also be too high for highly sensitive persons. Recent research shows that a human odorant receptor, ORD7D4, is involved in sensitivity to androstenone. If the ORD7D4 genotypes of consumer and expert panels are known, this might facilitate consumer studies in the future. There is still a great need for rapid on/at-line detection methods in abattoirs for identifying carcasses with unacceptable levels of boar taint compounds. Several emerging rapid technologies with a potential for boar taint detection have been investigated. They represent various measurement principles such as chemical sensor arrays (electronic noses), mass-spectrometry fingerprinting, ultra-fast gas chromatography, gas-phase spectrometry and biosensors. An industrial detection method should allow 100% correct classification of both acceptable and not-acceptable samples with regard to boar taint sorting criteria. There are, however, still too high a percentage of false negatives ranging from 5% to 20%. In addition, these methods do not yet seem to fulfil the industrial specifications with regard to cost efficiency, simplicity and analysis time. There is still no dedicated measurement technology available for on/at-line detection of boar-tainted carcasses that measures both androstenone and skatole.     

Effect of a gonadotropin-releasing factor vaccine on follicle-stimulating hormone and luteinizing hormone concentrations and on the development of testicles and the expression of boar taint in male pigs

The objective of this study was to determine the effect of using a gonadotropin-releasing factor (GnRF) vaccine on follicle-stimulating hormone (FSH) and luteinizing hormone (LH) concentrations in plasma, the size of testicles, and the expression of boar taint in male pigs. Vaccinated pigs were compared with surgically castrated pigs and entire males. Pigs were randomly assigned to three treatment groups: surgically castrated during the first week of life (T01, n = 274), immunized twice during the fattening period with a GnRF vaccine, the first when 13 to 14 wk of age and the second when 20 to 21 wk of age (T02, n = 280), and entire males (T03, n = 56). From a subgroup of both T01 and T02 and from all pigs of group T03, blood samples were collected immediately before second vaccination (T02) and again before slaughter at either 24 to 25 or 26 to 27 wk of life to determine the plasma concentrations of LH and FSH. Testicles were removed after slaughter and their size was determined. Meat and fat samples from all pigs of T02 and T03 as well as 25% of the pigs of T01 were examined with the cold cooking and fat melting test. Immediately before the second vaccination (T02 only), LH and FSH concentrations were not significantly different between T02 and T03. However, LH and FSH concentrations were significantly higher in T01 compared with T02 and T03. Before the first slaughter date, LH and FSH concentrations were significantly lower in T02 than in T03. Testicle size was significantly lower in T02 compared with that in T03. In T02, 98% (235 of 239) of the samples were rated negative for boar taint by the cooking test, whereas in T03, 94% (48 of 51) were rated positive. In the fat melting test, 97% of T02 were rated negative and 3% (7 pigs) were rated positive, including the pigs tested positive in the cold cooking test. In T03, 94% were rated positive. All pigs (7 of 239) in T02 that were positive for boar taint in the cooking or melting test and that were tested had androstenone and skatole concentrations in backfat below threshold levels of 1 μg/g and 0.2 μg/g, respectively.     

Skatole metabolites in urine as a biological marker of pigs with enhanced hepatic metabolism

Boar taint is a quality defect in meat, related to accumulation of skatole and androstenone in male pigs. The levels of skatole and its main metabolites in plasma and urine samples were measured with a validated liquid chromatography-MS method and related to activity of hepatic cytochrome P450 (CYP450) in order to identify ‘fast metabolizing’ pigs. Urine (n=46), blood (n=12), liver (n=25) and adipose tissue (n=46) were sampled from a total of 46 entire male pigs. Skatole levels in fat were negatively correlated to CYP2E1 activity and positively to 3-hydroxy-3-methyloxindole (HMOI), indole-3-carboxylic acid (ICA) and 2-aminoacetophenone in urine. HMOI and ICA levels in urine were the best predictors of high skatole levels in fat. In summary, the present study provided further evidence for the key role of CYP2E1 in skatole metabolism and suggested that measurement of HMOI and/or ICA in urine might provide information about skatole levels in live pigs.