Prediction of body weight on the basis of body measurements in mature indigenous chickens in Senegal
E F Guèye*, A Ndiaye** and R D S Branckaert***
Senegalese Institute of Agricultural Research (ISRA), PO Box 2057, Dakar-Hann, Senegal
*Present address (Animal Production Service, Animal Production and Health Division,
FAO, Viale delle Terme di Caracalla, 00100 Rome, Italy)
** Directorate of Livestock (DIREL), Ministry of Livestock, PO Box 67, Dakar, Senegal
***Animal Production Service, Animal Production and Health Division, FAO, Rome, Italy
Abstract
Data on body weight and body measurements were individually collected from mature
Senegalese indigenous fowls at two central poultry markets in Dakar, Senegal, between
March and September 1998, with the objective to investigate the possibilities of using
body measurements to predict the body weight of birds with high level of accuracy.
Results, obtained from 502 males and 325 females, revealed that more males (60.7 %) were
removed from fowl flocks for sale. The males showed higher body weights and body
measurements (P<0.001).
Correlation coefficients between the body weight and the circumference of chest were
strong and high (P<0.001 in males as well as in females). The body weight was also
correlated to the body length (P<0.001 in males and P<0.01 in females). Thus, the
circumference of chest and the body length are the body measurements that are most
suitable for the prediction of the body weight.
Key words: Body measurement, body weight, indigenous chicken, Senegal
Introduction
Poultry keeping is of great importance to Senegalese households. Outside the urban
centres, and especially in non-coastal areas, family poultry provides the population with
a vital source of protein and income, and plays a key role within the context of many
social events (eg: special banquets for family or for distinguished guests, cocks as alarm
clocks for people, gifts, etc.) and/or religious ceremonies (eg: cocks as offerings to the
deities). This industry is largely based on domestic chicken production. In 1995, the
chicken population in Senegal was estimated to be 40 million (Anonymous 1996), and more
than 70 % of it are constituted by the indigenous chickens (Guèye and Bessei 1997; Guèye
1998a). In Senegalese rural areas, indigenous chickens are generally raised in free-range
and/or backyard systems, which are traditional extensive husbandry systems (Guèye 1997).
Despite the importance of this subsistence poultry sector in Senegal, the marketing system
is quite informal and poorly developed. The price of chicken largely depends on body
weight. However, there is generally no weighing machine or scale available in poultry
markets and in villages.
The objective of this study was to investigate the possibilities of using body
measurements to predict the body weight of mature Senegalese indigenous chickens with high
level of accuracy.
Materials and methods
Location
The data of the present study were collected from indigenous chickens at two central
poultry markets of Dakar, the capital city of Senegal. These markets were chosen because
high populations of indigenous chickens are available at these places at all times. Birds
are brought there for sale regularly, especially on Mondays. Traders usually come to buy
chickens in village markets and/or from village producers and/or from middlemen and resell
them in markets of big cities, like those of Dakar.
Collection of data
Using a 20 kg weighing instrument and a measuring tape, information on body weight and
body measurements was individually collected from all chickens found during 12 visits to
the two markets from March to September 1998. Body measurements included body length (BL),
circumference of chest (CC), femur (F), crus (C), tarsometatarsus (TM), as described by
Salomon (1996). Measurements were carried out as follows:
- BL: Length between the tip of the Rostrum maxillare (beak) and that of the
Cauda (tail, without feathers). The bird's body should be completely drawn
throughout its length.
- CC: Circumference of the chest taken at the tip of the Pectus (hind breast).
- F: Length between the mid region of the Coxa (hip bone) and that of the Genu
(knee).
- C: Length between the mid region of the Genu and that of the Regio tarsalis.
- TM: Length between the mid region of the Regio tarsalis and the outset of the Digitus
pedis IV.
Statistical analysis
As subclass frequencies were unequal, the General Linear Models Procedure was applied
to the body weight and body measurements, and to calculate least square means. The
following statistical model was used:
Yij = µ + Si + eij
where, Yij = estimated value for the body weight or body measurement; µ =
population mean (mean that would exist if all classes had equal numbers); Si =
fixed effect of sex; eij = residual error
Pearson’s correlation coefficients were estimated between BW and all body
measurements. Data were subject to linear and multiple regression for predicting BW.
Results and discussion
| Table 1: Mean values for body
weight and body measurements |
![]() |
|
Mean ± standard
deviation
(No. of birds) |
|
| Traits |
(Males; n=502) |
(Females; n=325) |
Signif. |
![]() |
| Body weight (g) |
1367 ± 304 |
1120 ± 239.9 |
*** |
Body measurements (cm) |
|
|
|
| Body length |
40.8 ± 2.79 |
37.7 ± 2.30 |
*** |
| Chest circumference |
28.3 ± 2.81 |
25.7 ± 2.11 |
*** |
| Femur |
10.4 ± 1.57 |
9.5 ± 1.15 |
*** |
| Crus |
13.7 ± 1.60 |
12.0 ± 1.35 |
*** |
| Tarsometatarsus |
10.7 ± 1.09 |
9.20 ± 0.90 |
*** |
![]() |
| *** P<0.001 |
The mean values for BW and body measurements with respect to the sex of Senegalese
indigenous chickens brought to markets for sale are presented in Table 1. In comparison
with the females, more males (60.7 %) were sold from indigenous chicken flocks. This
result confirmed previous findings reported by Kuit et al (1986) in indigenous
chickens and pigeons, Dafwang (1990) in indigenous chickens, ducks and guinea fowls and
Guèye (1998a,b) in indigenous chickens. Guèye (1998a,b). However Otchere et
al (1990) asserted that both males and females of indigenous chickens, guinea fowls, ducks
and pigeons are sold. According to the report on pigeons by Hassan and Adamu (1997),
more males were also sold (54.9 % of 344 surveyed indigenous pigeons from 14 strains),
although pigeon flocks are normally composed of pairs. Nevertheless, mating possibilities
do exist since males and females are usually allowed to run together all the time in and
around the compound of households, indigenous chicken flocks not being closed production
units.
The males showed higher values of BW and body measurements (P<0.001). This agrees
with reports of Ngou Ngoupayou (1990) in indigenous chickens, Missohou et al (1997) in
indigenous chickens and Hassan and Adamu (1997) in indigenous pigeons.
Although information on the age of the birds could not be obtained because indigenous
chicken traders were ignorant of it, even most indigenous chicken keepers do not know the
exact age of their birds (Buldgen et al 1992), the average body weights of the surveyed
indigenous chickens indicated that they were probably about 6 months of age, because Sall
(1990) reported similar values for indigenous chickens at this age under extensive
husbandry systems of villages.
Throughout the year, indigenous chickens are regularly sold at markets. During the
period of this study, prices of surveyed indigenous chickens were not affected by the sex
of birds. Using a dressing percentage of 80 %, dressed birds at markets were estimated.
Their prices ranged from US$ 2.25 to 3.30 per kg. They are consistent with the estimated
average indigenous chicken meat prices in 1995 in Dakar which varied from US$ 2.54 to US$
3.93 per kg at markets and supermarkets, respectively (Guèye 1998a). According to Guèye
(1998a), these amounted to premiums of about 13 % at markets and 27 % at supermarkets in
comparison with the estimated prices of meat from commercial chickens. Thus, well-off
people who shop in supermarkets appear willing to pay more in order to get indigenous
chicken meat (Guèye 1998a). Furthermore, compared with chicken meat from commercial
flocks derived from imported stocks, those from indigenous stocks are strongly preferred
by Senegalese consumers (Guèye and Bessei 1996, 1997).
| Table 2: Correlation coefficients between
body weight (BW) and body measurements (values for males are above the dotted line and
those for females are below) |
![]() |
|
BW |
BL |
CC |
F |
C |
TM |
![]() |
| BW |
- |
0.68*** |
0.74*** |
0.43*** |
0.34*** |
0.52*** |
| BL |
0.37** |
- |
0.48*** |
0.66*** |
0.72*** |
0.68*** |
| CC |
0.80*** |
0.27* |
- |
0.24* |
0.18ns |
0.26** |
| F |
0.00ns |
0.46*** |
–0.14ns |
- |
0.68*** |
0.62*** |
| C |
0.10ns |
0.59*** |
0.00ns |
0.70*** |
- |
0.73*** |
| TM |
0.21ns |
0.54*** |
0.01ns |
0.48*** |
0.61*** |
- |
![]() |
| ns = non significant (P>0.05); * = P<0.05;
** = P<0.01; *** = P<0.001 |
The correlation coefficients between BW and body measurements for both males and
females are given in Table 2. All significant values of correlation coefficients were
found to be positive. In males, all body measurements were strongly correlated to the BW
of mature Senegalese indigenous chickens (P<0.001), while the BW of females was
correlated only to BL (P<0.01) and to CC (P<0.001). With regard to the BW of birds,
highest correlation coefficients were found with BL and CC, in males as well as in
females. In indigenous pigeons, Hassan and Adamu (1997) also observed that body length as
well as chest width were strongly and significantly correlated to body weight.
| Table 3: Prediction of body weight (BW,
g) on the basis of body length (BL, cm) or/and circumference of chest (CC, cm) |
![]() |
| Sex |
Regression equations |
R2 |
Significance |
![]() |
| Male |
BW = –1653 + 74.0 BL |
0.46 |
*** |
| Male |
BW = –899 + 80.2 CC |
0.55 |
*** |
| Male |
BW = –2138 + 45.4 BL + 58.4 CC |
0.69 |
*** |
| Female |
BW = –346 + 38.8 BL |
0.14 |
** |
| Female |
BW = –1230 + 91.3 CC |
0.64 |
*** |
| Female |
BW = –1747 + 17.2 BL + 86.1 CC |
0.67 |
*** |
![]() |
| ** = P<0.01; *** = P<0.001 |
The prediction equations consisting of body measurement variables are presented in
Table 3. The comparison of R2 values for such regression equations indicated
that, when multiple regression techniques based on BL and CC were used instead of linear
regressions, there were improvements of about 50 % to 25 % in R2 values for
males, and about 379 % to 5 % for females. Further addition of body measurements in
prediction equations did not make any substantial improvement in R2 values. BL
and CC represent higher values in comparison with the other body measurements and are
easier to measure. Thus relative errors, especially due to the "measurer", are
lower. It is therefore recommended to use multiple regression techniques based on BL and
CC.
Conclusion
This study was undertaken with the aim of using body measurements to predict the body
weight of mature Senegalese indigenous chickens. Thus, only using a measuring tape, it is
possible to predict the BW of these birds with high level of accuracy, BL and CC being
body measurements that are most suitable for this purpose. The measuring tape is much more
available than a weighing machine or a spring balance in poultry markets. These prediction
formulas can help consumers, who generally are not indigenous chicken keepers, to have an
accurate, easy, cheap and rapid estimation of the body weight of the birds. Furthermore,
in spite of the shortcomings of the source of data, an attempt was made to describe the
Senegalese indigenous chicken which shows a considerable variation in phenotypic traits
that are obviously affected by genetic components, in addition to the major impact of
environmental factors.
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