Rolf Claus

Physiological aspects of androstenone and skatole formation in the boar—A review with experimental data

The advantages of boars in fattening performance and carcass traits when compared with the other sexes are explained by testicular anabolic hormones. The steroid androstenone with a pronounced urine-like odour is the main objection against boar meat. More recently skatole (faecal odour) has been identified as another contributor to off-odour of pork. Androstenone is synthesized in the testes, secreted into the circulation and accumulated in adipose tissue due to its lipophilic property. Its biosynthesis is linked to the synthesis of anabolic testicular hormones. Therefore no practical method is available to maintain the sex-dependent anabolic potential of boars and to suppress androstenone selectively. Skatole is formed from tryptophan by specialized microbes in the colon when energy in the colon is limited. Gonadal hormones, but also growth hormone and IGF-1, favour its formation. Oestrogens, which are synthesized in high amounts in boar testes, decrease voluntary food intake, thus lowering the intestinal passage rate. Additionally oestrogens probably influence directly intestinal contractions via specific gut receptors. It appears, however, that glucocorticoids are more important. They counteract mitogenic hormones, such as IGF-1, ultimately leading to gut mucosal cell degradation. The resulting cell debris probably is the main source of tryptophan for microbial skatole formation. In contrast to androstenone, skatole formation can be easily suppressed by dietary means.

Parallel measurements of indole and skatole (3-methylindole) in feces and blood plasma of pigs by HPLC

Skatole and indole (partly) result from microbial degradation of tryptophan in the intestine and may cause an unpleasant fecal odour of pork. A high-performance liquid chromatography method was developed which allows serial measurements (sensitivity, 0.15 ng/ml plasma; coefficient of variation, 10%). Parallel measurements were carried out in blood plasma, drawn through indwelling catheters in the jugular vein and the vena cava, from five ovariectomized sows. Additional determinations were carried out in feces. Concentrations in feces (skatole, χ=2.3 μg/g; indole, χ=10 μg/g) were significantly correlated (P<0.001) with concentrations in jugular vein plasma. Skatole concentrations in plasma of vena cava (χ=0.54 ng/ml) were higher (P⩽0.001) than in peripheral plasma (0.32 ng/ml). In plasma of the portal vein, concentrations of skatole were 67 ng/ml and those of indole 120 ng/ml. It is concluded that changes in fecal concentration indicate similar changes in blood concentrations. Indole formation is higher than skatole formation and occurs mainly in the proximal part of the large intestine, so that the vena cava does not contribute to peripheral concentrations. Skatole formation also occurs in the distal part, and the vena cava plasma reflects considerable resorption, whereas indole concentrations do not differ significantly in both vessels.

Estrogens and prostaglandin F2α in the semen and blood plasma of stallions

Abstract A study was performed to determine the levels of estrogens and prostaglandin F 2 α in the stallion ejaculate. Simultaneous semen and blood plasma samples were collected from 19 stallions, 2 weeks apart, during the breeding season. Although not statistically different, the total mean estrogen content tended to be higher in seminal plasma (4447 pg/ml) than in blood (2497 pg/ml). A tendency was found for higher mean estrone sulphate concentrations than for total free steroid in both seminal (4116.1 vs 330.5 pg/ml) and blood plasma (2447.1 vs 49.5 pm/ml). Mean concentrations of estrone in ejaculate and blood plasma were 257.1 ± 267.0 (SD) and 9.5 ± 5.4 pg/ml, respectively. Estradiol-17β concentrations were 73.4 ± 87.4 and 40.0 ± 27.6 pg/ml in ejaculates and blood plasma, respectively. Mean PGF 2 α concentrations tended to be much higher than total estrogens (1106.8 ± 1636.4, SD, vs approximately 260 ng/ejaculate, respectively). To our knowledge this is the first report of PGF 2 α and estrogen concentrations in the stallion ejaculate.

Serum IgA-Promoting Effects Induced by Feed Loads Containing Isolated Deoxynivalenol (DON) in Growing Piglets

Deoxynivalenol (DON), a Fusarium toxin belonging to the trichothecene group, has been reported to produce a variety of adverse health effects in farm animals, such as inhibition of protein synthesis, reduction of feed intake, and alteration of the immune system. In pigs, the effects of increasing levels of chemically pure DON in a semisynthetic diet on performance, health, and serum immunglobulin A (IgA) levels were examined. A diet, without grain components and trichothecene free (8 main trichothecenes), with doses of 0, 300, 600, and 1200 μg pure DON/kg was fed to 34 female pigs for a period of 8 wk after weaning under standardized conditions. Body weight gain and biochemical and hematological values in the blood and serum, including concentrations of IgA, blood glucose, cortisol, and insulinlike growth factor 1 (IGF-1), were determined. Increasing levels of DON in the feed induced a significant depression of glucose levels. Cortisol and IGF-1 levels were not significantly affected but differed between groups at the end of the experiment. A significant increase of IgA concentration in the serum even at a dosage level of 600 μg DON/kg feed was observed. This is the first report demonstrating in vivo that limited dosages of DON are able to stimulate IgA levels in the serum of growing piglets.

Effects of resistant potato starch on odor emission from feces in Swine production units.

Odor emission from swine facilities is determined by microbial breakdown of amino acids or carbohydrates in the pig colon. It was the aim to influence apoptosis and thus amino acid availability for odor formation by feeding resistant starch (300 g kg(-1) feed) over the whole fattening period to 40 pigs. Concentrations of 12 key components (indoles, volatile fatty acids, methanethiol) were measured in feces and headspace over the slurry duct and compared to 40 normally fed controls in a separate compartment. Concentrations of substances resulting from amino acids were reduced in feces by 70% (indoles) and 8% (branched chain fatty acids) and in the headspace by 72% and 20%. Resistant starch only led to minor increases of straight chain fatty acid concentration. Maximal reduction occurred for 3-methyl-1H-indole (skatole) which is the main determinant of malodor so that the results point to promising strategies for reducing pig odor emission.

Individual return to Leydig cell function after GnRH-immunization of boars.

Immunization of boars against GnRH inhibits synthesis of testicular anabolic steroids and the sex odour androstenone. Time between second vaccination and return of Leydig cell function is unknown. Six catheterized boars received the second dose (Improvac) at 26 weeks of age (day 0). Titre, LH, testicular steroids, and IGF-I were determined in blood until testosterone exceeded 0.5 ng/mL again in all boars. At week 10 the titre was low again. Return of testicular function was preceded by increased pulsatile secretion of LH but onset of steroid synthesis was delayed and highly variable (10-24 weeks) and was not related to the initial antibody titre. A major reason for delayed onset of Leydig cell function apparently is a variable refractoriness against LH.

Expression of the monocarboxylate transporter 1 (MCT1) in cells of the porcine intestine.

Uptake of energy into cells and its allocation to individual cellular compartments by transporters are essential for tissue homeostasis. The present study gives an analysis of MCT1 expression and its cellular occurrence in the porcine intestine. Tissue portions from duodenum, jejunum, ileum, colon ascendens, colon transversum and colon descendens were collected and prepared for immunohistochemistry, Western blot and real time RT‐PCR. A 169 bp porcine MCT1 cDNA fragment was amplified and published. MCT1 mRNA expression in the large intestine was 20 fold higher compared to the small intestine. Western blot detected a single protein band of 41 kDa at a much higher amount of MCT1 protein in the large intestine vs. the small intestine. MCT1 protein was detected in mitochondrial fractions of the large but not the small intestine. Immunohistochemistry in the small intestine showed that immune cells in the lamina propria and in the lymphoid follicles primarily expressed MCT1 while in the colon epithelial cells were the main source of MCT1. In summary, cellular expression of MCT1 differs between epithelial cells in the colon and small intestine. A possible role of MCT1 for uptake of butyrate into immune cells and the overall role of MCT1 for intestinal immune cell function remains elusive.

Expression of 11β -hydroxysteroid -dehydrogenase 2 in Sertoli cells of boar testes

11beta-Hydroxysteroid-dehydrogenase 2 (11beta-HSD2) activity occurs in boar testes but it is not known which cell types express 11beta-HSD2 mRNA and protein. Therefore, testes samples were taken from mature boars. For immunocytochemistry and Western blot pig-specific antibodies were raised against a 10-amino acid peptide corresponding to amino acids 391-400 of the coding sequence. Quantitative PCR was performed in testis homogenates and additionally RT-PCR in samples collected by UV-single cell microdissection. Data show that in interstitial tissue 11beta-HSD2 is expressed in Leydig cells and additionally in blood capillaries. In tubuli, 11beta-HSD2 primarily is formed in Sertoli cells whereas occurrence in spermatogonia could not be definitely proven. Because glucocorticoid receptors were never found in boar Leydig cells, it is concluded that the expression of 11beta-HSD2 in several types of cells forms consecutive lines of defense to protect spermatogonia against glucocorticoid-induced apoptosis.

An improved microtitre enzyme immunoassay to measure the boar taint steroid 5α-androst-16-en-3-one in blood plasma of pigs

Androstenone (5α-androst-16-en-3-one) is a volatile steroid which is synthesized in boar testes and stored in high amounts in fat thus leading to an urine-like odor in pork. Whereas microtiter assays (MTA) exist for fat determination, measurement in blood with MTA was not yet possible. The system reported here is based on a specific antiserum and a horse radish peroxidase conjugate as tracer. For coating bovine serum albumin was avoided which otherwise would lead to unspecific binding. Blood plasma was extracted with n-hexane, solvent was evaporated in a vacuum centrifuge and the extract was taken up in buffer with 10% methanol. Assay sensitivity was 2.5pg/well (0.025ng/mL), specificity was confirmed by GC-MS (r=0.96; n=50) and inter- and intraassay variation were 4.9% and 5.9%, respectively. Thus an assay system is available for studies in pig production and in wildlife research due to pheromone activity also in other species.

Is the early postnatal rise of testosterone responsible for a later male pattern of growth hormone secretion in pigs

Sexual differentiation in Placentalia consists of several consecutive steps during fetal, postnatal, and premature development. It is known from male rats that an elevation in testosterone synthesis is observable within 2 d of birth, which leads to a male pattern of growth hormone (GH) secretion with low base levels and high amplitudes compared with that in females. In the male pig, a transient rise in testosterone concentration occurs about 4 wk after birth, but it is unknown whether it results in a later male pattern of GH secretion. In this study, male pigs (sus scrofa) were castrated either at 1 wk of age (Group 1, n=8) or at 6 wk of age (Group 2, n=8). Blood was sampled daily via cephalic vein catheters between 17 and 29 wk of age and analyzed for testosterone, GH, insulin-like growth factor-1 (IGF-1), and urea. High-frequency blood sampling (every 20 min over 24h) for determination of GH pulsatility was performed at ages 19 and 24 wk. Total fat content and protein synthesis were determined at age 25 wk and at slaughter, respectively. Comparing Groups 1 and 2, there were no differences in daily GH concentrations or pulsatile secretion patterns, but in both groups, mean GH levels and pulsatility decreased from Week 19 to Week 24. Consequently, IGF-1, protein synthesis, urea, and body fat showed no differences when comparing both groups. It is concluded that the postnatal rise of testicular steroidogenesis in male pigs is not responsible for the later male pattern of GH secretion.