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UTILIZATION OF BOAR MEAT: COMPOSITION, QUALITY AND ODOR INCIDENCE IN RELATION TO ANDROSTENONE AND SKATOLE¹

Purdue University, West Lafayette, IN 47907 and University of Alberta, Edmonton, Alberta T6G 2P5

	Abstract

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Carcasses and(or) tissues of 510 boars and 510 barrows were analyzed for lean content, muscle quality, incidence of objectionable odor, 5-androstenone concentration and skatole concentration. Boars and barrows differed (P < .01) in warm carcass weight (73.5 vs 80.1 kg), longissimus muscle area (36. vs 35. cm²), 10th rib fat depth (1.80 vs 2.57 cm), estimated percent muscle (56.1 vs 51.3%) and marbling score (1.73 vs 1.97). No difference (P > .05) was found for muscle color score (2.51 vs 2.45). Although odor panel scores were higher (P < .01) for boars than for barrows (1.74 vs 1.56), both scored quite low. The correlation coefficients between panel scores and 5-androstenone content (.13) and between panel scores and skatole content (–.14) were nonsignificant (P > .05). These results indicate that boars reared in U.S. commercial production facilities produce lean meat more efficiently than barrows do and they have a low incidence of offensive odor. Concentration of 5-androstenone and skatole in backfat proved unrelated to odor intensity.

Key Words: Boars • Meat • Boar Taint • Androstenone • Skatole

	Introduction

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Boar meat is produced and merchandized successfully in some countries, but the practice has not been widely tested or adopted in the U.S. (Malmfors and Lundstrom, 1983). Objectionable odor in boar meat has been attributed to the C₁₉-¹⁶ steroids androstenone and androstenol, to the tryptophan degradation product skatole, or to an interaction of the two types of materials (Lundstrom et al., 1980; Brennan et al., 1986). Lundstrom et al. (1980) reported that skatole enhances the sensory impression of boar odor as produced by androstenone.

A potential control point for boar odor exists at the time of slaughter. Andresen (1975) developed a radioimmunoassay for 5-androstenone and Desmoulin et al. (1982) established a threshold level of the hormone in fat of .5 µg/g for expression of undesirable odor in fresh meat. Danish workers (Mortensen and Sorensen, 1984) suggested that .24 ppm of skatole may be used as a rejection level for boar odor. Further work is needed to establish screening tests for either or both of these materials.

The objectives of this research were 1) to evaluate the carcass composition, muscle quality and odor incidence in group-reared boars and 2) to determine the concentrations of 5-Androstenone and skatole in boar fat and their relationships with odor intensity.

	Experimental Methods

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Yorkshire-Landrace-Duroc crossbred boars (510) and randomly selected littermate barrows (510) with mean weights of 24.4 and 24.0 kg, respectively, were penned in groups of approximately 28 on partially slatted floors. Pen allotments were made to maximize age uniformity within pens. Pigs had ad libitum access to a corn-soybean-based diet containing approximately 17.5 protein, .89% lysine and 8% added animal fat. They were slaughtered in commercial facilities during the months of September, October and early November at approximately 170 to 172 (SE =.45) d of age and carcasses were weighed within 45 min postmortem. At 8 to 12 h postmortem, the left carcass sides were sectioned at the 10–11th rib space and tracings of longissimus muscle area and s.c. fat were made on acetate paper. Longissimus muscle area was determined with a grid and fat depth was measured at a point that corresponds to three-fourths of the length of the longissimus cross-section beginning at the medial border. Color-firmness-structure scores (1 = pale, soft, exudative; 3 = normal; 5 = dark, firm, dry) and marbling scores (1 = traces, 3 = small, 5 = abundant; Rust and Topel, 1969) were derived by two trained people. Samples of backfat (100 g) were obtained at the 10th rib and frozen at –40°C for later analyses.

Backfat samples were thawed at 4°C for 24 h prior to odor evaluation. Samples weighing approximately 2 g were placed in capped 20-ml scintillation vials and heated on a hot tray at 100°C. The odor intensity of each sample was scored by a panel of eight women selected for their ability to detect androstenone. The odor intensity of all boar and barrow samples was scored on a scale of 1 to 6 (1 = no boar odor, 2 = very slight odor, 3 = slight odor, 4 = moderate odor, 5 = strong odor, 6 = very strong odor). Panelists evaluated up to 12 samples per day (6 boar, 6 barrow). The order of sample presentation within each set was randomized for each panelist. A reference sample of 4 µg of 5 -androst-16-en-3-one was provided. Further details of the sensory evaluation procedure were described by Brennan et al. (1986).

A subset of 46 backfat samples (restricted by time requirement and expense) was drawn randomly from the boar samples and assayed for 5-androstenone by radioimmunoassay as developed by Andresen (1975) and for skatole as described by Peleran and Bories (1985. Recovery rate of tritiated 5-androstenone added to backfat samples was 95 ± 2% and for skatole was 52 ± 1%. Sensitivity of the hormone assay was 50 pg and the intrassay coefficient of variation was 12.1%. HPLC was used for quantitation of skatole. A Waters⁶ model 45 solvent delivery system with model U6K injector was coupled to a Lichrosorb RP-18, 10 µm (4.6 x 250 mm) column. The mobile phase was methanol and water (60:40) at a flow rate of 1.5 ml/min. An Isco⁷ absorbance detector was used at 225 nm wavelength.

Boar-barrow comparisons for carcass composition, muscle quality and odor intensity were made by analysis of variance. Androstenone assays, skatole assays and odor intensity scores for the 46 sample subset were analyzed by correlation methods (Harvey, 1975).

	Results and Discussion

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The production system used in this study produced average live weights of 102.1 kg for boars and 107.6 kg for barrows. Boar carcasses also were lighter (P < .01) in weight than those of barrows (Table 1). In spite of that the boars produced weights of muscle per day of age (.243 kg) similar to those of barrows (.238 kg). These estimates are based on the regression equation derived by Forrest et al. (1988) using carcass weight, longissimus area and 10th rib fat depth. Boars also were more efficient converters of feed to live weight than barrows were producing feed efficiency ratios of 3.45 and 3.54, respectively. These results are consistent with most studies of boar feed efficiency (Walstra and Kroeske, 1968), but they differ from several reports on growth rate (Hansson, 1974; Siers, 1975; Wood and Riley, 1982). However, a few studies have shown that barrows have growth rates superior to those of boars (Walstra and Kroeske, 1968). Perhaps the performance of boars reared in large groups is lower than that of boars reared in experimental facilities because of social contact among animals and reduced feed intake.

Backfat from boars had higher (P < .01) scores for odor intensity than that from barrows, but both were relatively low (Table 1). Odor intensity scores were lower than those reported previously for animals of similar weight on which the same type of sensory panel and scoring system were used (Brennan et al., 1986). The scores averaged slightly below the "very slight odor" range on our scale, whereas the boar meat evaluated by Lundstrom et al. (1980) scored most frequently in the "obvious boar taint" range of their scale. It is not possible to identify the cause(s) of the relatively low levels of odor in these boars.

Analyses of 5-androstenone in 46 backfat samples revealed a mean value of 1.51 (SD = 1.04) µg/g. The correlation coefficient between androstenone and odor intensity score (.13) was nonsignificant (P > .05). Skatole analyses gave a mean value of .37 (± .20) µg/g. Correlation coefficients for skatole vs androstenone (–.02) and vs odor intensity score (–.14) also were nonsignificant (P > .05). The correlation coefficients between panel scores vs the sum of androstenone and skatole (.12) and the product of androstenone and skatole (.04) were nonsignificant (P > .05).

In contrast to lower than expected odor intensity scores, 5-androstenone concentrations in backfat averaged higher than the reported threshold for detection of odor by consumers (Desmoulin et al., 1982). This supports the view that androstenone expression as boar odor may be dependent on an interaction with other compounds such as skatole (Lundstrom et al., 1980). Based on this theory, when skatole concentration is low, the correlation of androstenone concentration with odor intensity scores would be low or nonexistent as found in this study. On the other hand, skatole concentration was higher than that reported by Lundstrom et al. (1980) who used different analytical methods. There is insufficient literature on skatole concentration as determined by HPLC to compare our skatole results with those of others. Nevertheless, the poor correlation between skatole and odor intensity score suggests that skatole is not a dependable indicator of boar odor.

	Implications

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The incidence of boar odor among boars reared in typical U.S. production environments and slaughtered at approximately 170 d of age is relatively low. Neither 5-androstenone nor skatole concentration in backfat was correlated with odor intensity score. Perhaps management systems for young boars may be developed that would reduce or nearly eliminate the problem of boar meat odor.

	Footnotes

 
¹ Journal Paper No. 12,008 of the Purdue Agric. Exp. Sta. Supported in part by research grants from Purina Mills, Inc., St. Louis, MO and National Pork Producers Council, Des Moines, IA. Conducted in the facilities of Murphy Farms, Rose Hill, NC and Lundy Packing Co., Clinton, NC.

² Dept. of Anim. Sci., Purdue Univ.

³ Present address: Dept. of Dairy and Anim. Sci., Pennsylvania State Univ., University Park 16802.

⁴ Dept. of Anim. Sci., Univ. of Alberta.

⁵ Present address: Agriculture Canada, Lacombe Research Sta., Bag 500, Lacombe, Alberta TOC 1S0.

⁶ Waters Associates, Division of Millipore Corp, Mil-ford, MA.

⁷ Isco, Lincoln NE.

Received for publication April 28, 1989. Accepted for publication July 27, 1989.

	Literature Cited

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Andresen, O. 1975. A radioimmunoassay for 5-androst-16-en-3-one in porcine adipose tissue. Acta Endocrinol. 79:619.[Abstract/Free Full Text]

Brennan, J. J., P. J. Shand, M. Fenton, L. L. Nicholls and F. X. Aheme. 1986. Androstenone, androstenol and odor intensity in backfat of 100- and 130-kg boars and gilts. Can. J. Anim. Sci. 66:615.

Desmoulin, B., M. Bonneau, A. Fronin and J. P. Bidard. 1982. Consumer testing of pork and processed meat from boars: The influence of fat androstenone level. Livest. Prod. Sci. 9:707.

Forrest, J. C., C. H. Kuei, M. W. Orcutt, A. P. Schinckel, J. R. Stouffer and M. D. Judge. 1988. Electromagnetic scanning, ultrasonic imaging and electronic probing for estimation of pork carcass composition. In: Proc. 34th Int. Congr. of Meat Sci. and Technol. p 31.

Hansson, I. 1974. Effect of sex and weight on growth, feed efficiency and carcass characteristics of pigs. 1. Growth rate and feed efficiency of boars, barrows and gilts. Swed. J. Agric. Res. 4:209.

Harvey, W. R. 1975. Least-squares analysis of data with unequal subclass frequencies. ARS H-4, USDA, Washington, DC.

Lundstrom, K., K.-E. Hansson, S. Fjelkner-Modig and J. Persson. 1980. Skatole–another contributor to boar taint. In: Proc. 26th Eur. Mtg. of Meat Res. Workers. p 300.

Malmfors, B. and K. Lundstrom. 1983. Consumer reactions to boar meat: A review. Livest. Prod. Sci. 10:187.

Malmfors, B. and R. Nilsson. 1978. Meat quality traits of boars in comparison with castrates and gilts. Swed. J. Agric. Res. 8:209.

Mortensen, A. B. and S. E. Sorensen. 1984. Relationship between boar taint and skatole determined with a new analysis method. In: Proc. 30th Eur. Mtg. of Meat Res. Workers. p 394.

Peleran, J. C. and G. F. Bories. 1985. Gas chromatographic determination and mass spectrometric confirmation of traces of indole and 3-methylindole (skatole) in pig back fat. J. Chromatogr. 324:469.[Medline]

Rust, R. E. and D. G. Topel. 1969. Standards for pork color, firmness and marbling. Iowa State University, Ames.

Siers, D. G. 1975. Live and carcass traits in individually fed Yorkshire boars, barrows and gilts. J. Anim. Sci. 41:522.[Abstract/Free Full Text]

Walstra, P. and D. Kroeske. 1968. The effect of castration on meat production in male pigs. World Rev. Anim. Prod. 4:59.

Wood, J. D. and J. E. Riley. 1982. Comparison of boars and castrates for bacon production. 1. Growth data, and carcass and joint composition. Anim. Prod. 35:55.

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