Effect of dietary crude protein content on skatole concentration in boar serum

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.

Review: Production and consumption of pork meat with different levels of boar taint / Revisión: Producción y consumo de carne de cerdo con diferentes niveles de olor sexual

Boar taint or sexual odor is a sensorial defect (a disagreeable smell) that occurs in some meat from entire male pigs. The main compounds responsible are androstenone and skatole stored in the fat of the animal. The main technique for reducing the androstenone level in the meat is by castration, either surgically or by immunocastration. Recent studies in the field of immunocastration appear to provide a solution to the androstenone problem by reducing the levels of this substance while taking advantage of the yield and carcass quality of entire male pigs. The quantity of skatole is mainly affected by the diet and handling of the pigs. The consumer decides whether to accept or reject the meat from male pigs according to the presence or absence of boar taint. However, variations in the consumer response depending on country, preparation and type of product consumed, as well as the individual's sensitivity to sexual odor, can be observed by looking at different works. According to some of these studies, UK, Irish, Canadian and US consumers will more readily accept meat from entire male pigs than consumers from France, Sweden, the Netherlands and Spain.

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.

The influence of sex (boars and gilts) on growth, carcass and pork eating quality characteristics

Boar and gilt pigs from three genotypes (with 0, 0·25 and 0·50 Duroc inclusion level) were reared from 30 to 90 kg live weight on seven feeding regimens which involved combinations of diet formulation and feeding level. A diet of conventional energy and protein level (CEP; 14·2 MJ/kg digestible energy, 205 g/kg crude protein, 10 g/kg lysine) and a diet of higher energy and lower protein (HELP; 14·7 M]/kg digestible energy, 166 g/kg crude protein, 7·0 g/kg lysine) were used. One treatment involved feeding the HELP diet ad libitum, with the other six treatments involving feeding the CEP diet ad libitum, restricted, or in combinations of ad libitum and restricted. A total of 721 animals comprising similar numbers of boars and gilts were used to estimate sex differences for growth performance, carcass and meat quality, and eating quality. Tissue growth rates were predicted from regression equations based on P2fat depths or ham-joint dissection, developed from subsamples of animals that were subjected to full-side dissection. Overall when compared with gilts, boars grew faster (838 v. 799 gtday, P < 0·001), had improved food conversion ratios (2·39 v.2-55, P < 0·001) but had similar daily food intakes and lean and subcutaneous fat growth rates. Lean tissue food conversions did not differ significantly between the sexes. Killing-out proportions were higher for gilts (0·766 v. 0·749 , P < 0·001), however P2 backfat thickness and lean proportions did not differ between the sexes. The firmness of the mid-back fat, assessed subjectively and using a penetrometer, was greater for gilts than for boars. The tenderness of pork loin chops, assessed by a trained sensory panel, was judged to be better for boars than for gilts but there was no sex difference in overall acceptability. The fat from boars had a higher level of abnormal odour and boar odour. There was a sex × dietary treatment interaction for boar odour with the HELP diet producing the highest levels and the biggest difference between the sexes for odour scores.

Influence of type and dietary rate of inclusion of non-starch polysaccharides on skatole content and meat quality of finishing pigs

The effect of feeding different sources of dietary fibre at varying rates of inclusion on the concentrations of skatole and indole in the backfat of finishing pigs and their subsequent carcass quality was studied. Sugar-beet pulp (SBP) and straw (S) were selected because of their assumed widely differing hind-gut fermentability characteristics. They were individually and in combination added to a diet at three rates of inclusion designed to provide concentrations of 40, 80 and 120 g non-starch polysaccharide (NSP) per kg. The digestible energy (DE) contents varied between the three levels of inclusion of NSP but were formulated to a lysine: energy ratio of 0.625 g: MJ DE with other amino acids being in the same individual proportion to lysine. The nine experimental diets were offered to 10 replicate (five entire males and five females) pigs of initial live weight 55 kg. Food intakes were adjusted between treatment to ensure that energy and nutrient intakes were common. Animals were slaughtered on reaching 85 kg live weight. Adipose tissue was analysed for skatole and indole and meat quality characteristics assessed. No significant differences in performance were detected although carcasses from animals given sugar-beet pulp were significantly fatter. There were significant correlations between the level of skatole in the backfat and the following eating quality characteristics: skatole odour intensity of the fat, abnormal odour intensity of fat, abnormal odour intensity of lean and abnormal flavour intensity of lean with correlations coefficients of 0·656 , 0·709 , 0·496 and 0·523 respectively (coefficients >0.276; P < 0·05). The range in skatole levels in the backfat were attributable substantially to very high levels found in three boars. No significant correlations were found between indole concentrations in the backfat and eating quality characteristics. However no effects of dietary NSP type or inclusion level on the eating quality characteristics of pig meat, with pigs given diets on the basis of equal energy and nutrient intakes, were detected.

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

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

Rapid determination of skatole and indole in pig back fat by normal-phase liquid chromatography

A rapid normal-phase high-performance liquid chromatographic method for the quantitative determination of indole and skatole in pig back fat samples has been developed. The compounds were extracted by shaking the samples at ambient temperature in hexane-2-propanol (92:8, v/v). The sample preparation procedure was simple because it was not necessary to remove the fat from the samples. The compounds were separated on a 250 x 4.6 mm I.D., 5 micron Hypersil aminopropylsilica column. Fluorescence (excitation at 280 nm and emission at 360 nm) was used for selective detection. Recoveries for skatole and indole, relative to the internal standard, were 10.3 +/- 0.9% and 99.6 +/- 4.4%, respectively. Linearity determined in fat samples was in the range of 0.05-1 microgram/g and the correlations observed were R2 = 0.9914 for the indole and R2 = 0.9916 for skatole.