Plasma skatole and androstenone levels in entire male pigs and relationship between boar taint compounds, sex steroids and thyroxine at various ages
Introduction
An unpleasant odour in heated pork, called boar taint, is caused principally by the presence of androstenone (5-alpha-androst-16-en-3-one) and skatole (3-methylindole) in the adipose tissue from some entire male pigs. The threshold levels of androstenone and skatole in fat are suggested to be from 0.5 to 1 μg/g and from 0.20 to 0.25 μg/g, respectively. Androstenone is synthesised in the testicles and skatole is produced from the amino acid tryptophan in the large intestine of pigs. Both compounds are metabolised in the liver. Androstenone levels increase at puberty in parallel with other testicular steroids; besides, the amount of expressed androstenone in fat is genetically regulated Bonneau, 1982, Sellier et al., 2000, Quintanilla et al., 2003. Skatole levels depend on genetic factors Lundström et al., 1994, Pedersen, 1998, feeding system (Jensen and Jensen, 1997), environmental conditions (Walstra et al., 1999) and the activity of liver enzymes involved in skatole metabolism Babol et al., 1998, Diaz and Squires, 2000. Factors involved in intestine development, such as IGF-1 or thyroid hormones, might be important for skatole production (Claus and Raab, 1999). Skatole levels vary with age Zamaratskaia et al., 2001, Babol et al., 2003 although the nature of these variations remains unknown. Skatole levels seem to increase at the age close to puberty (Babol et al., 2003) possibly as a result of an involvement of sex steroids in the regulation of skatole metabolism in the liver (Babol et al., 1999). Neither female nor castrated male pigs exhibit fat skatole in increased amounts, which also suggests that testicular steroids affect skatole levels.
Thyroid hormones are involved in puberty onset by affecting testis development (Cooke, 1996). Specific nuclear binding sites for thyroid hormones have been found in testis (Palmero et al., 1995). Thus, thyroid hormones might also affect variations of skatole and androstenone levels at puberty through affecting testicular functions.
Claus and Weiler (1985) suggested that puberty onset is related to photoperiod. The seasonal variations in the levels of androstenone and skatole Claus et al., 1983, Walstra et al., 1999 might also be explained by maturity related factors. Andersson et al. (1998b) have shown an effect of day length on off-odour expression in fat from male pigs at slaughter age, as evaluated by sensory methods.
The aims of the present study were to investigate the relationships between skatole, androstenone, testosterone, estrone sulphate and thyroxine in entire male pigs at various ages. The effect of day length on skatole and androstenone levels in plasma was also investigated.
Section snippets
Animals and sample collection
In total, 47 entire male pigs (Yorkshire×Hampshire), siblings from 13 litters, were included in this study. The pigs were part of a project on photoperiodic effects on pubertal maturation in crossbred boars (Andersson et al., 1998b). Details of treatments and animal handling are given in Andersson et al. (1998b). Briefly, siblings were randomly divided into groups with three lighting-controlled treatments: Control group, Spring/Summer group and Autumn/Winter group. The Control group was exposed
Results
Light regime affected neither skatole nor androstenone levels in plasma (P=0.12 and 0.42, respectively).
The mean concentrations of all investigated compounds at young (from 8 to 10 weeks), prepubertal (from 12 to 18 weeks) and slaughter (from 20 to 24 weeks) ages are given in Table 1. Plasma skatole levels varied with age (P<0.001) and were high at young age and significantly decreased between 10 and 12 weeks of age (P<0.001; Fig. 1; Table 1). At older age, the levels of skatole increased after
Discussion
In this study plasma concentrations of skatole were measured by a simplified HPLC method, after deproteinising the samples with an equal volume of acetonitrile. Since this method requires few manipulations during sample preparation and does not require the use of diethylether, which is a potential fire hazard, it may be useful in the routine laboratory setting.
Neither skatole nor androstenone levels in fat were significantly affected by photoperiod in the present study. Photoperiod was
Conclusions
Light regime affected neither skatole nor androstenone levels in plasma. Androstenone levels in plasma increased simultaneously with plasma levels of testosterone and estrone sulphate as puberty development progressed. Levels of skatole in plasma from some boars reached high values at young age, 8 and 10 weeks. This increase of skatole levels was related to no other investigated compounds. Further studies on the age-related changes in skatole levels are needed to determine the nature of skatole
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Present address: MRC Human Reproductive Sciences Unit, The University of Edinburgh, Chancellor's Building, 49 Little France Crescent, Old Dalkeith Road, Edinburgh EH16 4SB, UK.