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Poult Sci 2006. 85:1975-1979
© 2006 Poultry Science Association
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PHYSIOLOGY, ENDOCRINOLOGY, AND REPRODUCTION

Effects of Caponization and Different Exogenous Androgen on the Bone Characteristics of Male Chickens

K.-L. Chen*, S.-M. Tsay*, T.-Y. Lee* and P. W.-S. Chiou{dagger},1

* Department of Animal Science, National Chiayi University, Taiwan; and {dagger} Department of Animal Science, National Chung-Hsing University, Taichung, Taiwan

1 Corresponding author: wschiou{at}dragon.nchu.edu.tw


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The effects of caponization and androgen implantation on the bone characteristics of male chickens were evaluated. Healthy Single Comb White Leghorn cockerels were caponized or sham operated (sham) at 12 wk old. Sixteen birds from each group were selected for a 14-wk experiment in trial 1. Sixteen birds from the sham group and 64 from the caponized group (randomly allocated into 4 treatments) were implanted with 10.4 ± 0.4 mg (1.62-mm i.d., 3.6-mm o.d.) of cholesterol, testosterone (TES), 5{alpha}-dihydrotestosterone (5{alpha}-DHT), or 19-nortestosterone (19-NorT) and were assigned to trial 2 for a 14-wk experiment. The results from trial 1 showed that caponization increased BW (P < 0.05) and decreased tibia stress, ash content, and P content with higher blood P concentration (P < 0.05) as compared with the sham group. In trial 2, the cholesterol implantation group showed the lowest tibia breaking strength, bending moment, stress, and ash content (P < 0.05). The 19-NorT implantation group showed decreased (P < 0.05) blood Ca and P concentration but increased tibia ash and P content, reaching the same level as the sham group (P > 0.05). The adverse effects of caponization on bone characteristics could be improved using androgen implantation. Among the implantation groups, the 19-NorT implantation group showed the best improvement in tibia breaking strength and bending moment, followed by the TES and 5{alpha}-DHT groups. The TES group showed the best improvement in tibia stress, followed by the 19-NorT and 5{alpha}-DHT groups.

Key Words: bone characteristic • caponization • male chicken • testosterone


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Androgen has long been recognized as playing an important role in bone development, physiology, and metabolism (Oursler et al., 1996; Pederson et al., 1999). Caponization decreases the femur density and ash content in mature male rats (Wink and Felts, 1980). Depressed androgen through exposure to chemicals, testectomy operation, or age has adverse effects on bone growth and development in human beings (Manolagas et al., 2002).

However, the effects of caponization on poultry were inconclusive in earlier studies that showed no apparent effect (Landauer, 1937) or negative results (Leeson et al., 1976; Ono et al., 1979; Johnson and Rendano, 1984). Adverse effects of caponization were observed through bone component analysis, biomechanical properties, and histological observations in recent studies (Lin and Hsu, 2003; Chen et al., 2006). Tsay et al. (2004) showed a decrease in tibia weight, length, breaking strength, and bending moment in 26-wk-old male Leghorn chickens caponized at 12 wk old. The caponized (capon) group was implanted with low (5.9 ± 0.2 mg), medium (9.8 ± 0.2 mg), or high (16.7 ± 0.2 mg) doses of testosterone (TES), respectively. They concluded that medium-dose TES implantation showed the best improvement in bone strength and reached the same level as sham-operated (sham) male chickens in tibia weight, length, breaking strength, and bending moment.

Testosterone and its analogues [e.g., 5{alpha}-dihydrotestosterone (5{alpha}-DHT) and 19-nortestosterone (19-NorT)] showed different bioactivity and effects on chicken growth (Fennell and Scanes, 1992; Astiningsih and Rogers, 1996; Fennell et al., 1996). However, information on the consistency of various TES source effects on bone is still inconclusive. This study was conducted to investigate the effects of caponization and different forms of exogenous androgen implantation on the bone characteristics of male chickens.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Bird Management and Experimental Design
Healthy Single Comb White Leghorn male chickens with similar BW (mean ± SD, 636 ± 27 g) were caponized at 12 wk of age and housed in individual 40 x 30 x 38 cm cages. Sixteen intact and 16 caponized male chickens were selected for trial 1. For trial 2, 16 sham chickens and 64 caponized chickens were randomly divided into 4 treatments and implanted with cholesterol (CHOL; JAH05003, Hayashi Pure Chemical Industries Ltd., Osaka, Japan), TES (no. 86500, Fluka, Buchs, Switzerland), 5{alpha}-DHT (no. 10300, Fluka), or 19-NorT (no. 74640, Fluka) for a 14-wk experimental period (to 26 wk of age). Feed (ME, 2,873 kcal/kg; CP, 15.9%) and water were provided ad libitum during the trial. The testectomy procedure was performed according to Chen et al. (2000, 2005). The androgen implantation procedure was performed according to the modified method of Fennell et al. (1990; Chen et al., 2005). A 1-cm implantation tube (1.62-mm i.d., 3.6-mm o.d., 10.4 ± 0.4 mg; Tygon clear tubing, R-3603, Saint-Gobain, Courbevoie, France) was used in this trial. Cholesterol or different forms of androgen were implanted subcutaneously at the back of the chickens’ necks at 12, 16, 20, and 24 wk of age.

Measurement and Analysis
Body weights were measured at 12 and 26 wk of age. Chickens were killed at the end of the trials.

Bone Characteristics.
Tibias from individual chickens were dissected. After cleaning away the adherent tissues, the right tibia was defatted with chloroform-methanol (2:1) and dried at 105°C for 24 h to measure the bone weight, bone length, and biomechanical characteristics. The ultimate bone breaking strength (kg) was determined using a tension compression tester (DCS-5, Shimadzu Autograph, Shimadzu, Kyoto, Japan) with the 3-point bending test. The total distance between the 2 supporting ends was 6.5 cm. The test range was 0 to 100 kg and crosshead movement was 1 mm/sec. The bone bending moment (kg·cm) and stress (kg/cm2) were calculated according to Crenshaw et al. (1981).

The left tibia was prepared for tibia ash, Ca, and P content analyses. After precise weighing and pulverization, 1 g of tibia was used for tibia ash, Ca, and P content analyses according to the method of the Association of Official Analytical Chemists (1990). The Ca and P contents were determined using an atomic absorption spectrophotometer (model 2380, Perkin-Elmer, Wellesley, MA) and spectrophotometer (U2000, Hitachi Ltd., Tokyo, Japan), respectively.

Blood Constituents.
Blood samples were taken from the brachial vein of chickens that were withdrawn from food and water for 12 h at 26 wk of age. After centrifugation, the serum was stored at –40°C for further analysis. Serum Ca, P concentrations, and alkaline phosphatase activity were analyzed using an automatic blood chemical analyzer with Roche testing kits (COBAS MIRA plus, Roche Diagnostics, Rotkreuz, Switzerland).

Statistical Analysis
Analyses of variance among the treatment groups (trial 1: sham and capon; trial 2: sham, capon implanted with CHOL, TES, 5{alpha}-DHT, or 19-NorT) were calculated using the GLM procedure of SAS (SAS Institute, 1990). Duncan’s new multiple-range test was used to compare the means according to Steel and Torrie (1960).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Trial 1
Bone Characteristics.
Table 1Go shows the effects of caponization on bone characteristics in male chickens. Caponization increased the BW (P < 0.05). Caponization had no influence on tibia length, weight, relative tibia weight, breaking strength, bending moment, and Ca content (P > 0.05). Caponization reduced the tibia stress, ash, and P contents as compared with the sham group (P < 0.05).


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  		Table 1. Effects of caponization on bone characteristics in male chickens (trial 1)1
 
Caponization has been found to cause androgen deficiency, decreased fighting behavior, and reduced energy, which increases the body fat and BW in the capon group (Chen et al., 2000, 2005, 2006). These results were also observed in this trial. Neither femur or tibia abnormalities, nor differences in bending moment, were observed in this trial. This result did not agree with that from Johnson and Rendano (1984), who showed that 6-wk-old caponized Leghorn male chickens were more susceptible to osteochondrodysplasia and osteodysplasia in the tibiotarsus–tarsometatarsus region when compared with intact cockerels at 35 or 47 wk old. The discrepancy may be attributed to the use of younger capon (26 wk old) in this trial. Caponization showed no influences on the tibia length, weight, breaking strength, and bending moment (P > 0.05). The exception was tibia stress (P < 0.05). Stress was defined as force per unit of bone area. A more common term for stress is strength, although these terms are used interchangeably (Crenshaw et al., 1981). The measurement referred to both the force area and bending degree within this area, and it could be an indicator for bone mineralization. Tibia stress is attributed to the amount of bone mineralization, not resulting from Ca retention only (Leblond et al., 1950). Therefore, caponization showed no influence on the tibia Ca but reduced the ash and P contents. These observations imply that mineralization was more active in the sham group, resulting in increased bone stress measurements.

Androgen increases bone Ca and P retention and enhances the mineralization process (Schoutens et al., 1984; Wakley et al., 1991) and osteoblast ossification, but it inhibits osteoclast remodeling (Scheven et al., 1986; Kurihara et al., 1989). In this trial, caponization decreased the tibia ash and P contents (P < 0.05). This decrease was not found in the tibia Ca content (P > 0.05). Rath et al. (1996) indicated that TES implantation (10 mg/kg of BW per wk) could improve the physical properties of the tibia without changing the bone Ca content in 6-wk-old broilers. They proposed that androgen may change the bone collagen crosslink to enhance bone strength.

Blood Constituents.
Table 2Go shows the effects of caponization on blood characteristics in male chickens. Caponization increased the blood Ca and P concentrations (P < 0.05) but had no influence on alkaline phosphatase (P > 0.05).


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  		Table 2. Effects of caponization on blood characteristics in male chickens (trial 1)1
 
Bone ossification and resorption proceed incessantly. Blood Ca is the substrate for bone ossification and mineralization, whereas decreased androgen concentration enhances the osteoclasts bone corrosion and releases bone Ca and P (Manolagas et al., 2002). Therefore, caponization resulted in increased blood Ca and P concentrations. The results in this trial agreed with those of Lin and Hsu (2003), who found that caponization increased the blood Ca and P concentrations. Osteoblasts produce alkaline phosphatase, which increased significantly during the growing and laying periods; hence, osteogenic activity is positively related to blood alkaline phosphatase activity (Galvanovskii et al., 1985; Register et al., 1986; Bogin, 1992). However, caponization did not influence an increase in blood alkaline phosphatase activity in this trial (P > 0.05).

Trial 2
Bone Characteristics.
Table 3Go shows the effects of androgen implantation on bone characteristics in the CAPON group. The BW of androgen-implanted capon did not differ from the CHOL group (P > 0.05). The BW of the 19-NorT group was higher than that of the sham group (P < 0.05). The breaking strength, bending moment, and stress of the CHOL group were the lowest among all groups (P < 0.05). The breaking strength and bending moment in the 19-NorT group were higher (P < 0.05), and the stress in the TES group was higher (P < 0.05) than those in the CHOL group. The sham and 19-NorT groups showed the highest tibia ash (P < 0.05), followed by the 5{alpha}-DHT group (P < 0.05). The TES and CHOL groups showed the lowest (P < 0.05) among all groups. The tibia Ca and P contents of the sham group were the highest (P < 0.05) among all groups, followed by the 19-NorT, 5{alpha}-DHT, and TES groups (P > 0.05).


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  		Table 3. Effects of androgen implantation on bone characteristics in caponized chickens (trial 2)1
 
Fennell and Scanes (1992) indicated that 2-wk-old caponized male chicks were implanted with different doses of TES (2.6, 8.9, or 29.2 mg) until 12 wk of age. The high TES dose and all 5{alpha}-DHT or 19-NorT doses inhibited BW and tibia growth. The high-19-NorT dose caused death in the capon group. In this trial, the implantation dose was similar to the medium dosage in the Fennell and Scanes (1992) trial. However, all androgen implantation sources did not influence BW and tibia length and weight (P > 0.05). The 5{alpha}-DHT and 19-NorT implantations did not promote capon growth. Interestingly, the BW of 19-NorT group was heavier than that in the sham group. This implied that 19-NorT implantation in 12- to 26-wk-old chickens promotes growth. These results differed from the results of Fennell and Scanes (1992), who used 2-wk-old chicks for a 10-wk implantation trial. These differences may be attributed to the older age (12 wk old) of the chickens used in this trial.

Pederson et al. (1999) showed that androgen receptors are present in the avian skeleton, as well as in the mammalian skeleton. Androgen, therefore, enhances osteoblast ossification and inhibits osteoclast corrosion, therefore presenting better tibia breaking strength in intact male chickens. In this trial, all of the androgen implantations used showed no influence on tibia length, weight, and relative weight (P > 0.05). Androgen implantation improved the adverse biomechanical property effects of caponization to the same level exhibited in the sham group (P > 0.05). The best tibia breaking strength and bending moment improvement was found with 19-NorT implantation, followed by TES and 5{alpha}-DHT implantation. Testosterone implantation showed the best tibia stress improvement, followed by 19-NorT and 5{alpha}-DHT implantation. Bone biomechanical property is affected by the types and forms of molecular crosslink in collagens, and, therefore, androgen effectively strengthens the collagen fibers and enhances the tibia breaking strength (Frost, 1994; Rath et al., 1996) in the implanted capon. Rath et al. (1996) reported that TES implantation enhanced tibia stress in 6-wk-old broilers. This was similar to the result in this trial. Implantation with 19-NorT resulted in increased tibia ash, Ca, and P content, greater than that produced by TES and 5{alpha}-DHT (P < 0.05), reaching the same level as that in the sham group (P > 0.05). This implied that androgen implantation can improve the adverse effects of androgen deficiency on tibia mineralization. The effectiveness was in the following order: 19-NorT > 5{alpha}-DHT > TES.

Blood Constituents.
Table 4Go shows the effects of androgen implantation on blood characteristics in the CAPON group. The 19-NorT implantation decreased the blood Ca and P concentrations (P < 0.05), compared with the CHOL group. Otherwise, there were no differences in blood Ca and P concentrations (P > 0.05) among the other implantation groups. Different androgen implantations did not influence the alkaline phosphatase activity as compared with the CHOL group (P > 0.05); however, the sham group showed the lowest (P < 0.05) alkaline phosphatase activity.


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  		Table 4. Effects of androgen implantation on blood characteristics in capons (trial 2)1
 
Androgen promotes bone formation, Ca and P retention (Johnson and Rendano, 1984; Fennell and Scanes, 1992; Miller, 1992). The most effective anabolic ability among androgen sources was exhibited by 19-NorT (Fennell and Scanes, 1992). Hence, the 19-NorT group showed the highest bone Ca and P contents (Table 3Go), with the lowest blood Ca and P concentrations among all implantation groups (P < 0.05). The alkaline phosphatase activity, however, was not affected by the source of exogenous androgen implantation (P > 0.05). This result was consistent with the results of Tsay et al. (2004), using the same TES implantation dose. The sham group exhibited the lowest alkaline phosphatase activity. This higher activity in implantation groups may be attributed to the stress from the implantation procedure, which was performed every 4 wk. However, this conclusion requires further confirmation.


   ACKNOWLEDGMENTS
 
We thank the National Science Council of Taiwan (Taipei) for financially supporting this project. This project number is NSC 93-2313-B-005-010.

Received for publication March 7, 2006. Accepted for publication May 17, 2006.


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 REFERENCES
 
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