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Brazilian Journal of Poultry Science

Print version ISSN 1516-635X

Rev. Bras. Cienc. Avic. vol.16 no.2 Campinas Apr./June 2014

http://dx.doi.org/10.1590/1516-635x160297-100 

Classification of the coefficients of variation of parameters evaluated in Japanese quail experiments

 

 

Leal DHVI; Faria Filho DE deII; Oliveira EMBIII

IZootecnista
IIDepartamento de Zootecnia, Universidade de São Paulo, Faculdade de Zootecnia Engenharia de Alimentos, Pirassununga, São Paulo, Brasil
IIIInstituto de Ciências Agrárias da Universidade Federal de Minas Gerais, Montes Claros, Minas Gerais, Brasil

Corresponding author

 

 


ABSTRACT

The objective of this study was to design a classification range of the coefficients of variation (CV) of traits used in experiments with eggtype Japanese quails (Coturnix coturnix japonica). The journal Revista Brasileira de Zootecnia was systematically reviewed, using the key word 'quail' during the period of January, 2000 to 2010. The CV of feed intake (g/bird/d), egg production (%/bird/d), egg weight (g), egg mass (g/bird/d), feed conversion ratio per dozen eggs (g/dozen), feed conversion ratio per egg mass (g/g), and egg specific gravity (g/mL) were collected. For each parameter, CV were classified using the following median (MD) and pseudo-sigma (PS) ratio as follows: low (CV < MD – PS), medium (MD – PS < CV < MD + PS), high (MD + PS < CV < MD + 2PS) and very high (CV > MD + 2PS). According to the results, it was concluded that each parameter has a specific classification range that should be taken into account when evaluating experimental precision.

Keywords: Coturnix coturnix japonica, experimental statistics, experimental precision


 

 

INTRODUCTION

The coefficient of variation is obtained by the residual standard deviation as a percentage of the general mean of the experiment. Therefore, it measures experimental precision because the residual standard deviation is the square root of residual mean square, which contains all the variation due to experimental error. In addition, the CV allows comparing experiments, independently of the unit used.

In experiments with Japanese quails, there are reference values of specific CV that identify classification ranges relative to their degree of precision, as it happens in pig production (Judice et al., 1999), beef cattle (Judice et al., 2002), equine nutrition (Lana et al., 2006), broilers (Mohallem et al., 2008), and commercial layers (Faria Filho et al., 2010).

Therefore, the distribution of CV values in experiments with Japanese quails need to be studied, as most researchers have compared their results with the classification suggested by Gomes (2000) as low, when CV values are lower than 10%; medium, with CV values between 10 and 20%, high, with CV value between 20 and 30%, and very high, when CV values are higher than 30%.

Amaral et al. (1997) and Judice et al. (1999) suggest that the normality of CV distribution should be determined to establish variability ranges. However, working with upland rice crops, Costa et al. (2002) presented a new method of CV classification that can be applied with data do not have normal distribution. This method is based on the use of median and pseudo-sigma, instead of mean and standard deviation.

In order to obtain a consistent compilation of published studies, the method of systematic literature review can be used (Castro et al. 2002). This is a scientific technique to review literature, using specific methods to identify, select, and critically analyze relevant studies. Therefore, search strategy, databases, period of review, and criteria for the inclusion of studies must be previously defined. All these aspects should be mentioned in the text. Excluded articles must be mentioned and their exclusion justified. This will render these systematic reviews reproducible and, in general, unbiased.

This study aimed at verifying if the parameters evaluated in experiments with Japanese quails (Coturnix coturnix japonica) have specific classification ranges of the coefficient of variation by using the method of systematic literature review for data collection and the method of Costa et al. (2002) to classify the CV.

 

MATERIALS AND METHODS

The systematic literature review (Castro et al., 2002) was carried out using the journal Revista Brasileira de Zootecnia of issues published between January, 2000 and January, 2010. The website of Sociedade Brasileira de Zootecnia (Brazilian Society of Animal Science) was accessed (www.sbz.org.br; access in April, 2010) and the path revista → revista on-line → entrar → consulta por palavra-chave (journal → online journal → enter → search key word) was followed. The key word used was "quail" to search in Portuguese the fields title, key words, and abstract.

Studies with egg-type Japanese quails (Coturnix coturnix japonica) during lay and presenting CV for at least one of the following parameters were selected: feed intake (g/bird/d), egg production (%/bird/d), egg weight (g), egg mass (g/bird/d), feed conversion ratio per dozen eggs (g/dozen), feed conversion ratio per egg mass (g/g), and egg specific gravity (g/mL).

The number of observations, minimum and maximum values, mean and standard deviation were calculated. The median (MD) was calculated according the equation: MD = (Q1 + Q3)/2, where Q1 is the first quartile and Q3 is the third quartile. pseudo-sigma (PS) was calculated according to the equation: PS = (Q3 – Q1)/1.35 (Tukey, 1977). Data normality was evaluated by the Cramer-Von-Mises test. Analyses were carried out using SAS® software package (Littell et al., 2002).

CV ranges were determined according to the methodology proposed by Costa et al. (2002) as a function of MD and PS. The following CV ranges were determined: low (CV < MD – PS), medium (MD – PS < CV < MD + PS), high (MD + PS < CV < MD + 2PS), and very high (CV > MD + 2PS).

 

RESULTS AND DISCUSSION

The systematic literature review found 41 articles, out of which 24 were selected: Araújo et al. (2007), Barreto et al. 2007 a, 2007 b, 2007 c, 2007 d), Costa et al. (2007), Costa et al. (2008 a, 2008 b), Costa et al. (2009), Freitas et al. (2005), Mori et al. (2005), Moura et al. (2008), Murakami et al. (2006), Oliveira et al. (2009), Pinheiro et al. (2008), Pinto et al. (2002), Pinto et al. (2003 a, 2003 b), Ribeiro et al. (2003), Rizzo et al. (2008), Silva et al. (2002), Silva et al. (2003), Soares et al. (2007), and Umigi et al. (2007).

The number of observations, minimum and maximum values, mean, standard deviation, median, pseudo-sigma, and Cramer-Von-Mises test results of the CV values of the evaluated parameters are presented in Table 1. Only feed intake CV values presented normal distribution, and therefore the methodology proposed by Costa et al. (2002) was applied to establish CV classification ranges because it does not assume data normality.

Table 2 shows the CV classification ranges for the main parameters used in Japanese quail experiments.

The parameter egg specific gravity is highlighted as its classification range is very narrow, which indicated it is a very stable parameter. The same behavior of egg specific gravity results was found by Faria Filho et al. (2010) in experiments with commercial layers. On the other hand, feed conversion ratio per egg mass presented the widest CV classification range.

The classification of coefficients of variation in the present study should be used as reference by researchers to verify if the CV results obtained, and consequently the precision of their experiments, are within the acceptable range of values. When comparing the classification ranges used in the present study with that proposed by Gomes (2000), in which CV values lower than 10% are considered low, between 10 and 20%, medium; between 20 and 30%, high; and higher than 30% are very high, it is clear that this proposed range does not apply to Japanese quails. For instance, 8% CV would be considered low in the classification of Gomes (2000), but according to our classification, it is very high for the parameters egg weight and egg specific gravity. This difference may be due to the fact that the proposal of Gomes (2000) is based on agronomic parameters. Moreover, there is considerable variation among animal species, and there are specific classifications for pigs (Judice et al., 1999), beef cattle (Judice et al., 2002), equine nutrition (Lana et al., 2006), broilers (Mohallem et al., 2008), and commercial layers (Faria Filho et al., 2010).

 

CONCLUSIONS

It is concluded that there is a specific classification range for each parameter evaluated in egg-type Japanese quails (Coturnix coturnix japonica) that should be taken into account when evaluating experimental precision.

 

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Corresponding author
Daniel Emygdio de Faria Filho
Universidade de São Paulo, Faculdade de Zootecnia Engenharia de Alimentos
Av. Duque de Caxias Norte, n. 225, Campus da USP, CEP 13635-900, Pirassununga, São Paulo, Brasil
E-mail: fariafilho@usp.br

Submitted: June/2013
Approved: April/2014

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