Summary Castration has long been a traditional practice in the United States. Research studies indicate that intact males grow more rapidly, utilize feed more efficiently and produce a higher-yielding carcass with less fat and more edible product. The disadvantages of the intact male include aggressive behavior (bull and boar); undesirable odors and flavors (boar and ram); lower quality grade (bull); lower meat tenderness (bull and ram) and undesirable meat color (bull and ram). Research is needed to develop antemortem and(or) postmortem handling procedures that offset the disadvantages of the intact male so that the meat and livestock industry can take advantage of their rapid

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Utilization of the Intact Male for Red Meat Production: A Review

16-Unsaturated C19 steroids a review of their chemistry, biochemistry and possible physiological role

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.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/82E8C97D8465ADE22651FC9B046329B5/S1751731108003674a.pdf/div-class-title-biochemical-nutritional-and-genetic-effects-on-boar-taint-in-entire-male-pigs-div.pdf

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

Compounds responsible for boar taint, with special emphasis on androstenone: A review

Comparison of 16-androstene steroid concentrations in sterile apocrine sweat and axillary secretions: interconversions of 16-androstenes by the axillary microflora--a mechanism for axillary odour production in man?

1. The formation of androst-16-enes from [4-(14)C]progesterone has been investigated with long-term incubations and short-term kinetic studies. After 4hr., 1.7 and 10.3% respectively of 3alpha- and 3beta-hydroxy-5alpha-androst-16-enes were formed in boar testis minces, but much smaller yields were obtained in boar adrenal. Both tissues formed small quantities of androsta-4,16-dien-3-one. 2. The amounts of androst-4-ene-3,17-dione and testosterone isolated were small, suggesting that androst-16-ene formation may occur preferentially in the boar testis. 3. In the absence of tissue no radioactive androst-16-enes were formed. 4. Incubation of both [4-(14)C]pregnenolone and [7alpha-(3)H]progesterone resulted in 3alpha- and 3beta-hydroxy-5alpha-androst-16-enes containing (3)H/(14)C ratios of near unity and confirmed that both C(21) steroids were precursors. A similar incubation with 17alpha-hydroxy[4-(14)C]-progesterone and [7alpha-(3)H]progesterone gave the same Delta(16)-alcohols, but they contained only (3)H, indicating that side-chain cleavage of pregnenolone and progesterone occurred before 17alpha-hydroxylation. 5. Dehydroepiandrosterone, testosterone, testosterone acetate and 16-dehydroprogesterone were not found to be precursors of Delta(16)-steroids. 6. A pathway is proposed for the biosynthesis of 3alpha- and 3beta-hydroxy-5alpha-androst-16-enes from pregnenolone and progesterone; this may involve androsta-4,16-dien-3-one as an intermediate, but excludes 17alpha-hydroxyprogesterone, testosterone and dehydroepiandrosterone.

The biosynthesis of some androst-16-enes from C21 and C19 steroids in boar testicular and adrenal tissue.

1. The metabolism of [4-(14)C]pregnenolone to androst-16-enes has been studied in short-term incubations of boar testis tissue. With fresh tissue androsta-5,16-dien-3beta-ol (8%) and 5alpha-androst-16-en-3beta-ol (2%) were formed. Tissue that had been stored at -20 degrees C was still capable of metabolizing pregnenolone to androsta-5,16-dien-3beta-ol. 2. NADPH was essential for the formation of androsta-5,16-dien-3beta-ol from pregnenolone; NADH had less activity and ATP was not necessary for the reaction. 3. [4-(14)C]Androsta-5,16-dien-3beta-ol, prepared biosynthetically from [4-(14)C]pregnenolone, was shown to be converted by boar testis preparations into androsta-4,16-dien-3-one (31%) if NAD(+) was present or into 5alpha-androst-16-en-3beta-ol (4%) if NADPH was present. 4. 17alpha-Hydroxyandrost-4-en-3-one and 3beta,17alpha-dihydroxypregn-5-en-20-one were considered as possible precursors for androst-16-ene formation, but both were shown to be ineffective. 5. No radioactivity was incorporated into androst-5-en-3beta-ol used to trap any corresponding (14)C-labelled compound formed from [4-(14)C]pregnenolone.

The biosynthesis of androst-16-enes in boar testis tissue

The identification of c19-16-unsaturated steroids and estimation of 17-oxosteroids in boar spermatic vein plasma and urine

1. The formation of the two 16-unsaturated alcohols 5α-androst-16-en-3α-ol and 5α-androst-16-en-3β-ol from [5α-3H]5α-androst-16-en-3-one has been demonstrated in boar testis homogenates. 2. The optimum yield (23%) of the 3α-alcohol was obtained in the presence of NADPH, whereas that for the 3β-alcohol (74%) was obtained when NADH was the added cofactor. 3. The two alcohols were not interconvertible. 4. Prolonged storage of boar testis tissue at −20°C abolished the ability to form all androst-16-enes except androsta-4,16-dien-3-one from [4-14C]progesterone. 5. The production of 5α-androst-16-en-3-one and the two alcohols from [7α-3H]androsta-4,16-dien-3-one only occurred when fresh tissue was used, whereas reduction of [5α-3H]5α-androst-16-en-3-one was unaffected by storage of testis at −20°C. 6. NADPH was the preferred cofactor for the reduction of androsta-4,16-dien-3-one. 7. The previously established conversion of androsta-5,16-dien-3β-ol into androsta-4,16-dien-3-one was shown to be reversible, NADH and NADPH being equally effective cofactors. 8. Pathways of biosynthesis of 5α-androst-16-en-3α- and 3β-ols, with the C19 3-oxo steroids as intermediates, are presented.

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16-Unsaturated C19 3-oxo steroids as metabolic intermediates in boar testis

1. In one experiment [7α-3H]pregnenolone was infused continuously for 12min into the left spermatic artery of a sexually mature boar and blood was collected during this period by continuous drainage from the spermatic vein. After infusion, the testis was removed and immediately cooled to −196°C. 2. From both the testicular tissue and the spermatic venous plasma, 3H-labelled 16-unsaturated C19 steroids were isolated and characterized and their radiochemical purity was established. 5α-Androst-16-en-3α- and 3β-ol occurred mainly as sulphate conjugates and to a lesser extent as free steroids. Only traces of these alcohols occurred as glucosiduronate conjugates. 5α-Androst-16-en-3-one was found in the free (ether-extractable) fraction. 3. The isotope concentration of each of the 3H-labelled 16-unsaturated C19 steroids in testicular tissue was different from that in spermatic venous plasma. 4. The ratios of tritiated 5α-androst-16-en-3α- and 3β-ol (free steroids) to their respective sulphate conjugates in the testicular tissue were less than the ratios of the same compounds in the spermatic venous plasma. The possibility that the sulphates are partially hydrolysed by testicular sulphatases before secretion is discussed. 5. In a second experiment, a continuous close-arterial infusion of [7α-3H]pregnenolone into the left testis was performed over a 200min period and all the urine that accumulated during the infusion was collected for analysis. 6. No 3H-labelled 16-unsaturated C19 steroids were detected in the urine as free steroids. Only a trace of 5α-androst-16-en-3α-ol was detected conjugated as glucosiduronate, whereas the corresponding 3β-alcohol occurred mainly as glucosiduronate and to a lesser extent as sulphate. 7. The absence of 5α-androst-16-en-3β-ol glucosiduronate in the spermatic venous blood and its presence in considerable amount in the urine may be attributed to hepatic glucuronyl transferase activity.

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D. B. Gower

Papers

The biosynthesis of some androst-16-enes from C21 and C19 steroids in boar testicular and adrenal tissue.

The biosynthesis of androst-16-enes in boar testis tissue

The identification of c19-16-unsaturated steroids and estimation of 17-oxosteroids in boar spermatic vein plasma and urine

16-Unsaturated C19 3-oxo steroids as metabolic intermediates in boar testis

Studies on the biosynthesis in vivo and excretion of 16-unsaturated C19 steroids in the boar