Selected morphometric parameters and mineral density of tibiotarsal bones in green-legged partridge cockerels and capons

Abstract

K e y w o r d s: caponization, bones, bone mineral density, testosterone. A b s t r a c t The aim of this study was to determine the effect of caponization on selected morphometric parameters and mineral density of tibiotarsal bones in Green-legged Partridge cockerels. The experiment was conducted on 200 cockerels. At 8 wks of age, 100 birds were surgically castrated. At 12 and 24 wks of age, blood samples were collected from 10 intact cockerels and 10 capons, and the birds were slaughtered. Tibiotarsal bones were dissected from individual birds. Age had a significant effect on tibia weight in both cockerels and capons (P ≤ 0.01), whereas the effect of castration on this parameter was noted in older birds, at 24 wks of age (age x sex category interaction, P ≤ 0.01). Tibiotarsal bones were longer in cockerels than in capons (P ≤ 0.01). The tibiotarsal bones of capons had higher BMD values than the bones of cockerels (P < 0.01).

Full text

POLISH JOURNAL OF NATURAL SCIENCES
Abbrev.: Pol. J. Natur. Sc., Vol 33(1): 49–58, Y. 2018
SELECTED MORPHOMETRIC PARAMETERS
AND MINERAL DENSITY OF TIBIOTARSAL BONES
IN GREEN-LEGGED PARTRIDGE COCKERELS
AND CAPONS
Magdalena Zawacka1, Daria Murawska1, Anna Charuta2,
Michał Gesek3, Tomasz Mieszczyński1
1 Department of Commodity Science and Animal Improvement
University of Warmia and Mazury in Olsztyn, Poland
2 Institute of Health
Siedlce University of Natural Sciences and Humanities, Poland
3 Department of Pathological Anatomy
University of Warmia and Mazury in Olsztyn, Poland
K e y w o r d s: caponization, bones, bone mineral density, testosterone.
Abstract
The aim of this study was to determine the effect of caponization on selected morphometric
parameters and mineral density of tibiotarsal bones in Green-legged Partridge cockerels.
The experiment was conducted on 200 cockerels. At 8 wks of age, 100 birds were surgically
castrated. At 12 and 24 wks of age, blood samples were collected from 10 intact cockerels and
10 capons, and the birds were slaughtered. Tibiotarsal bones were dissected from individual
birds. Age had a significant effect on tibia weight in both cockerels and capons (P ≤ 0.01),
whereas the effect of castration on this parameter was noted in older birds, at 24 wks of age
(age x sex category interaction, P ≤ 0.01). Tibiotarsal bones were longer in cockerels than
in capons (P ≤ 0.01). The tibiotarsal bones of capons had higher BMD values than the bones
of cockerels (P < 0.01).
Address: Daria Murawska, University of Warmia and Mazury in Olsztyn, ul. Oczapowskiego 5,
10-719 Olsztyn, Poland, phone: +48 (89) 523 41 28; e-mail: daria.murawska@uwm.edu.pl

Magdalena Zawacka et al.
50
WYBRANE CECHY MORFOMETRYCZNE ORAZ GĘSTOŚĆ
MINERALNA KOŚCI PISZCZELOWO-STĘPOWEJ KOGUTÓW
I KAPŁONÓW ZIELONONÓŻKI KUROPATWIANEJ
Magdalena Zawacka1, Daria Murawska1, Anna Charuta2, Michał Gesek3,
Tomasz Mieszczyński1
1 Katedra Towaroznawstwa Ogólnego i Doświadczalnictwa
Uniwersytet Warmińsko-Mazurski w Olsztynie, Polska
2 Instytut Nauk o Zdrowiu
Uniwersytet Przyrodniczo-Humanistyczny w Siedlcach, Polska
3 Katedra Anatomii Patologicznej
Uniwersytet Warmińsko-Mazurski w Olsztynie, Polska
S ł o w a kl u c z o w e: kapłonienie, kości, gęstość mineralna kości, testosteron.
Abstrakt
Celem badań było określenie wpływu kastracji i wieku na wybrane cechy morfometryczne
oraz gęstość mineralną kości piszczelowo-stępowej kogutów zielononóżki kuropatwianej. Materiał
do badań stanowiło 200 kogutów, z których 100 poddano kastracji chirurgicznej w wieku 8. tygo-
dni. W wieku 12. i 24. tyg. od 10 losowo wybranych kogutów i 10 kapłonów pobrano próby krwi,
a następnie po uboju wypreparowano kość piszczelowo-stępową.
Stwierdzono, że wiek ptaków wpłynął istotnie na masę kości piszczelowo-stępowej kogutów
i kapłonów (P ≤ 0.01), natomiast wpływ kastracji ujawnił się u ptaków starszych, w wieku 24. tyg.
(interakcja wiek × kategoria płciowa, P ≤ 0.01). Kość piszczelowo-stępowa była dłuższa u kogu-
tów, w porównaniu z kośćmi kapłonów, zarówno w 12., jak i w 24. tyg. (P ≤ 0.01). Kości kapłonów
wykazywały wyższe wartości BMD (P < 0.01).
Introduction
In Europe, the meat of capons (surgically castrated male chickens) is
appreciated by consumers for its tenderness and avor, and it is more
expensive than meat from broiler chickens and organic chickens (Muriel
Durán 2004, Franco et al. 2016). Caponized chickens of native breeds are
most popular. Recent years have witnessed a growing interest in native
chicken breeds which are well adapted to extensive egg and meat produc-
tion systems (PaDhi 2016). Male layer-type chicks of native breeds, which
are considered “waste products” in the egg industry, are often used for
capon production. The Green-legged Partridge is one of such breeds.
Castration is a hormonal intervention which permanently inuences
metabolic processes in birds (rikiMaru et al. 2011, aDaMski et al. 2016).

Selected Morphometric Parameters and Mineral Density of Tibiotarsal Bones... 51
Due to reduced synthesis of sex steroids, caponization leads to increased
fat deposition in the carcass, which was conrmed by post-mortem analy-
ses, chemical analyses of muscles and histological analyses in castrated
birds (Díaz et al. 2010, Gesek et al., 2017). Age and sex exert signicant
effects on bone tissue parameters during postnatal development (charuta
et al. 2013). Androgens promote bone formation, Ca and P retention (John-
son and renDano 1984), whereas androgen deciency is a risk factor for
low bone mineral density (BMD) (Finkelstein et al. 1987). In poultry,
adverse changes are most frequently observed in the tibia. Research shows
that the volumetric mineral density of tibiotarsal bones in males of various
poultry species decreases at different ages, e.g. at 4 wks of age in broiler
chickens (charuta et al. 2013) and at 9 wks of age in turkeys (charuta
et al. 2012).
Some studies (lin and hsu 2003, chen et al., 2014) have revealed
that castration affects the weight, length and histological parameters
of bones. Muszyński et al. (2017) reported lower breaking strength of tibio-
tarsal bones in castrated males, which could be a risk factor in capon pro-
duction. According to ManolaGas et al. (2002), blood Ca is the substrate
for bone ossication and mineralization, whereas decreased androgen con-
centrations contribute to osteoclast formation, bone erosion, and Ca and P
release from bones. In contrast, MahMuD et al. (2014) found that caponiza-
tion had no signicant osteometric effects on almost all long bones. The
results of studies investigating the effects of castration on the qualitative
and quantitative parameters of bones are inconclusive, most likely due to
differences in the origin and age of caponized birds. Testosterone levels
also vary across breeds, which is another important consideration (Gry-
zińska et al. 2011, Murawska et al. 2015).
The objective of this study was to determine the effect of caponization
and age on selected morphometric parameters and mineral density of
tibiotarsal bones in Green-legged Partridge cockerels.
Materials and Methods
The experiment was conducted on 200 Green-legged Partridge cocke-
rels. Day-old birds were weighed, marked with wing tags, and randomly
distributed to 10 pens in the experimental center of the Department
of Commodity Science and Animal Improvement of the University of War-
mia and Mazury in Olsztyn, Poland. The birds were raised to 24 wks
of age, and were fed commercial diets ad libitum (Table 1). At 8 wks of age,
100 birds were surgically castrated by a qualied veterinarian in accor-

Magdalena Zawacka et al.
52
dance with Commission Regulation (EC) No. 543/2008. The procedure was
approved by the Local Ethics Committee in Olsztyn, Poland. The birds
were divided into two sex categories (with 5 replications per group and 20
birds per replication).
Table 1
Composition of experimental diets. Composition of diets 1 and 2: ground cereal grain (cornmeal,
ground wheat), soybean meal (line 40-3-2), calcium carbonate, monocalcium phosphate,
sodium chloride
Nutritional value of diets Diet 1 (weeks 1–8) Diet 2 (weeks 9–24)
Metabolizable Energy [MJ kg-1]* 11.64 11.94
Crude protein [%] 18.77 20.88
Crude fat [%] 2.81 3.64
Crude ash [%] 5.22 5.47
Crude ber [%] 2.51 2.55
Lysine [%] 0.94 1.08
Met + Cyst [%] 0.72 0.75
Threonine [%] –0.80
Tryptophan [%] –0.24
Methionine [%] –0.52
Calcium [%] 0.77 0.87
Total phosphorus [%] 0.59 0.59
Sodium [%] 0.18 0.14
Mineral-vitamin premix [%] 1.0 1.0
* Metabolizable energy content estimated based on the percentages of selected ingredients deter-
mined analytically
Provided per kg of diet: microelements: Cu – 8.0 mg, Fe – 116.0 mg, Mn – 80.0 mg, Zn – 100.0 mg,
J – 0.80 mg, Se – 0.20 mg. Vitamins: vitamin A (E 672) – 13200 IU, vitamin D3 (E671) – 3120 IU,
vitamin E – 68.0 mg, vitamin K3 – 4.80 mg, vitamin B1 – 2.2 mg, vitamin B2 – 7.2 mg, vitamin B6
– 5.0 mg, vitamin B12 – 44.0 mg, vitamin H (biotin) – 136 mcg, niacin – 44.0, Ca-D-pantothenate
– 18.0 mg.
At 12 and 24 wks of age, blood samples were collected from 10 intact
cockerels and 10 capons, and the birds were slaughtered (electrical stun-
ning followed by cutting the jugular vein). Blood samples were collected
from 10 randomly selected birds from each treatment to determine testo-
sterone levels. Blood was collected into test tubes containing heparin. Fre-
shly collected blood was centrifuged twice (MPW-350R centrifuge, MPW
MED INSTRUMENTS; 5 minutes, 10000 rpm), and each time the superna-
tant was transferred to 1.5 ml Eppendorf Safe-Lock micro test tubes with
an Eppendorf automatic electronic pipette. Plasma samples were frozen at
-72°C in 1.5 ml Eppendorf Safe-Lock micro test tubes in the Kaltis 390
ultra low temperature laboratory freezer. Testosterone levels were analy-
zed by radioimmunoassay (RIA) with the use of commercial kits supplied

Selected Morphometric Parameters and Mineral Density of Tibiotarsal Bones... 53
by DIAsource TESTO – RIA – CT (DIAsource ImmunoAssays S.A., Bel-
gium). Serum Ca and P concentrations, and alkaline phosphatase activity
were analyzed using an automatic blood chemistry analyzer and Roche
testing kits (COBAS MIRA plus, Roche Diagnostics, Rotkreuz, Switzer-
land).
Live body weight (BW) was determined before slaughter. Carcasses
were chilled for approximately 18 h at a temperature of 4°C, and carcass
dissection was performed. Tibiotarsal bones were dissected from indivi-
dual birds. The length of right bones was measured with a caliper accurate
to 1 mm. The structure of bone tissue (BMD – Bone Mineral Density, cor-
tical/compact and cancellous/spongy bone combined) was determined by
computed microtomography using the SkyScan 1174 scanner (Bruker –
SkyScan, Belgium) and the following software: CT-Analyzer, Nrecon,
CT Vox and DataViewer. The data were analyzed using Nrecon 1.6.9.18,
CTAnalyser 1.14.4.1+, CTVox 2.1.0 r741 and DataViewer 1.5.1.2 packa-
ges. The values of BMD were determined for a Hounseld units (HU)
range of –1000 to 0. The analyzed area was the proximal metaphysis of the
tibiotarsal bone.
The statistical analysis involved the determination of arithmetic
means (x) and standard deviations (SD). The data were analyzed by two-
way ANOVA (age × sex category; A × B: 2 × 2). The results were processed
using Statistica 2010 software.
Results
At 12 wks of age, Green-legged Partridge cockerels and capons were
characterized by similar average body weight of 1194 g and 1206 g, respec-
tively, which increased to 2030.6 g and 2067.6 g at 24 wks of age. Caponi-
zation had no signicant effect on the body weights of birds, which were
inuenced only by age (P ≤ 0.01, Table 2).
At 12 wks of age, tibia weight was similar in cockerels and capons
(10.01 g and 9.79 g, respectively), whereas at 24 wks of age, it was higher
in cockerels (15.38 g vs. 13.17 g, P ≤ 0.01, Table 2). Age had a signicant
effect on tibia weight in both cockerels and capons (P ≤ 0.01), whereas the
effect of castration on this parameter was noted in older birds, at 24 wks
of age (age x sex category interaction, P ≤ 0.01, Table 2).
Tibia length was affected by both the age of birds and castration
(P ≤ 0.01, Table 2). Cockerels had longer tibiotarsal bones than capons,
both at 12 and 24 wks of age (P ≤ 0.01, Table 2).

Magdalena Zawacka et al.
54
Table 2
Body weights and selected tibia parameters in 12- and 24-week-old Green-legged Partridge
cockerels and capons (mean ± SD)
Item Sex
category
Age [wks] P-value
12 24 age sex
category
A· S
interaction
Body weight
[g]
cockerels 1194.40 2030.8
0.000 0.241 0.227
±80.20 ±107.845
capons 1206.00 2067.80
±48,44 ±40.95
Tibia weight
[g]
cockerels 10.01 *15.38
0.000 0.005 0.023
±0.43 ±0.76
capons 9.79 13.17
±0,27 ±0,48
Tibia length
[cm]
cockerels *12.46 *14.88
0.000 0.028 0.670
±0.13 ±0.34
capons 11.48 13.98
±0.34 ±0.20
Bone
mineral
density
(BMD)
[g cm-3]
cockerels 0.98 1.80
0.000 0.000 0.247
±0.09 ±0.11
capons *1.62 *2.32
±0.15 ±0.14
*– values in columns (cockerels an capons of age group) differ signicantly
Caponization had a signicant effect on the mineral density of tibio-
tarsal bones. The tibiotarsal bones of capons had higher BMD values than
the bones of cockerels, both at 12 and 24 wks of age (P < 0.01, Table 2).
BMD values increased with age, from 0.098 g/cm2 and 0.0162 g cm-2 in
12-wk-old cockerels and capons, respectively, to 0.180 g cm-2 and 0.232 g cm-2
in 24-wk-old birds (P < 0.01, Table 2).
Age signicantly inuenced the blood concentrations of Ca and P, and
the activity of alkaline phosphatase (P ≤0.01, Table 3). At 12 wks of age,
blood Ca concentration reached 13.90 mg dl-1 in cockerels and 10.67 mg dl-1
in capons (P < 0.01), and blood P levels were determined at 6.92 mg dl-1 in
cockerels and 8.44 mg dl-1 in capons (P < 0.01). At 24 wks of age, blood Ca
concentration was comparable in cockerels and capons (9.38 mg dl-1 and
9.00 mg dl-1, respectively), and a similar trend was noted in blood P con-
centration (cockerels – 3.83 mg dl-1, capons – 3.85 mg dl-1). Caponization
increased the blood concentrations of Ca and P, but only at 12 wks of age
(age × sex category interaction, P ≤ 0.01, Table 3). The surgical procedure
had no inuence on the activity of alkaline phosphatase (Table 3).

Selected Morphometric Parameters and Mineral Density of Tibiotarsal Bones... 55
Table 3
Effect of caponization on selected blood parameters and testosterone levels in Green-legged
Partridge cockerels and capons (mean ± SD)
Item Sex
category
Age [wks] P-value
12 24 age sex catego-
ry
A· S
interaction
Ca
[mg dL-1]
cockerels *13.91 9.38
0.000 0.021 0.027
±0.17 ±0.18
capons 10.67 9.00
±0.16 ±0.17
P
[mg dL-1]
cockerels 6.92 3.83
0.000 0.025 0.003
±0.062 ±0.076
capons *8.44 3.85
±0.086 ±0.748
Alkaline
phosphatase
[U L-1]
cockerels 756.3 523.2
0.000 0.321 0.247
±0.04 ±0.06
capons 804.3 476.8
±0.02 ±0.01
Testosterone
[ng ml-1]
cockerels *0.40 *1.86
0.000 0.000 0.247
±0.04 ±0.06
capons 0.13 0.11
±0.02 ±0.01
*– values in columns (cockerels an capons of age group) differ signicantly
The effectiveness of surgical castration was conrmed by an analysis
of blood testosterone levels, which increased with age and were signi-
cantly (P < 0.01) higher in cockerels than in capons (Table 3).
Discussion
The present study investigated whether surgical castration inuences
morphometric parameters and the mineral density of tibiotarsal bones in
Green-legged Partridge cockerels and capons. Testosterone stimulates the
activity of osteoblasts in the bone formation process, as well as the ossi-
cation of long bones. Therefore, the absence of sex steroids in cockerels
could affect bone metabolism (MahMuD et al. 2014, Muszyński et al. 2017).
Our ndings indicate that the castration-induced decrease in blood testos-
terone levels had no effect on the body weights of Green-legged Partridge
cockerels and capons, but it signicantly affected the analyzed morpho-
metric parameters and mineral density (BMD) of tibiotarsal bones (Table 2).

Magdalena Zawacka et al.
56
At 24 weeks of age, the tibiotarsal bones of Green-legged Partridge cocker-
els were longer and heavier than the bones of capons. In
a study of male Taiwan country D × L2 cockerels, chen et al. (2006b) noted
lower weight of tibiotarsal bones in capons, whereas the length of the ana-
lyzed bones was not affected by castration. In an experiment performed on
male Single Comb White Leghorns (chen et al. 2007), caponization
decreased the length of tibiotarsal bones but had no inuence on bone
weight. The results of our study and the ndings of other authors point to
different responses of cockerels of various breeds to reduced testosterone
levels. It should also be noted that Taiwan country D × L2 cockerels (chen
et al. 2006b) were caponized at 10 wks of age, Single Comb White Leg-
horns (chen et al. 2007) were caponized at 12 wks of age, and Green-
legged Partridge cockerels analyzed in this study were surgically castrated
at 8 wks of age.
In the current study, capons were characterized by higher BMD va-
lues than cockerels, both at 12 and 24 wks of age. In a study of Polbar
chickens caponized at 8 wks of age, no signicant differences in the min-
eral density of tibiotarsal bones were found between intact males and
capons (Muszyński et al. 2017). It should be stressed, however, that in the
cited study, caponization had a benecial inuence on the body weights of
birds, which was not observed in the present experiment. The above results
suggest that male birds of various breeds may differ in their susceptibility
to changes resulting from decreased synthesis of steroid hormones.
chen et al. (2006a) demonstrated that caponization increased total
blood Ca concentrations. However, in a study by chen et al. (2007), capo-
nization had no inuence on total blood Ca levels. In the current study, an
increase in the blood concentrations of Ca and P was observed in 12-wk-old
capons, i.e. 4 wks after castration, whereas 24-wk-old cockerels and capons
(16 wks after castration) were characterized by similar blood Ca levels
(Table 3). The signicant decrease in blood Ca concentrations, noted in
capons 4 wks after castration, resulted from declining testosterone levels.
The stimulation of osteoclast formation and the release of Ca from bones
contributed to the stabilization of blood Ca levels, which were comparable
in 24-wk-old cockerels and capons.
lin anD hsu (2003) analyzed Taiwan country cockerels (TLRL native
chicken Taishi No. 13) and found no differences in blood Ca concentrations
between 28-wk-old cockerels and capons; capons had only higher blood
P levels. According to lin anD hsu (2003), caponization increases blood
ionized Ca concentrations, but not total Ca levels. chen et al. (2006a)
reported that caponization did not affect plasma alkaline phosphatase
levels, which is consistent with our ndings.

Selected Morphometric Parameters and Mineral Density of Tibiotarsal Bones... 57
The results of this study indicate that caponization exerted a signi-
cant effect on the analyzed morphometric parameters and mineral density
of tibiotarsal bones in Green-legged Partridge cockerels. However, further
research involving a higher number of parameters is needed to determine
whether the observed changes could pose a risk in capon production.
Tranlaslated by aleksanDra PoPrawska
Accepted for print 18.01.2018
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