On the evaluation of chicken egg shape variability

HAVLICEK, M. , NEDOMOVA, S. , SIMEONOVOVA, J., SEVERA, L. , KŘIVANEK, I. : On the evaluation of chicken egg shape variability. Acta univ. agric. et silvic. Mendel. Brun. , 2008, LVI, No. 5, pp. 69–74 Although recently reported models for determining egg shape are highly accurate, certain com pli cated measurements or computations are to be performed. Thus relatively simple and attainable analysis methods of chicken egg shape variability were chosen and used for the purpose of presented research. Sample of 250 eggs of ISA BROWN strain was examined. Geometrical parameters were measured and calculated with following expression of their coeffi cient of variation – namely egg length 3.56 %, egg maximum width 2.84 %, shape index 3.80 %, surface area 5.08 %, and egg volume 7.23 %. The second method consisted in shape quantitative measuring by the score of the principal components of elliptic Fourier descriptors (EFDs). The fi rst four principles components which could explain over 99 % of the egg shape variations were found to be very good measures of the monitored phenomenon. It was found that 87.41 % of the total shape variation can be accounted to length to width ratio. Usefulness and relevance of the shape index usage was confi rmed. chicken egg, shape variability, elliptic Fourier analysis Description of chicken egg shape is important for numerous applications and studies. Generally, when talking about avian eggs (both domestic and wild species), the knowledge of their geometric parameters is relevant to a number of studies, such as po pu la tion and ecological morphology (Mand, 1998), pre dic ting chick weight (Narushin et al., 2002), egg hat cha bi li ty (Narushin and Romanov, 2002), shell quality (Altuntas and Şekeroglu, 2008), egg interior pa ra me ters, avian biology, taxonomy, classifi cation, reproduction, poultry selection, genetics, and processing. There is a natural variability in egg shape. High variability of egg shapes creates diffi culties in their description. Egg shape evaluation can be performed by two ways: (a) by mathematical equations, and (b) by diff erent indices, which show the deviation of a true shape from some model object. Cha ra cte riza tion of egg’s shape by use of two indices: (a) egg length to a maximum width ratio (shape index) and (b) the ratio of long and short sections of the longitudinal axis of the egg a er division by the axis of maximum diameter, was proposed by Schonwetter (1960). Other indices were used by Kostin, 1977 (index of displacement of the axis of maximum diame ter from the middle point of egg length, index of pear-shapedness, index of conicity); Myand, 1988 (index of sphericity, oviformity, pear-shapedness, plumpness); Klimov, 1993 (index of equality, index of zone diff erences, index of roundness; Narushin, 2001 (index of ellipticity and conicity), and others. Usage of the indices, which refl ect all possible varia tions in egg shape, leads to a contradiction: on one hand, it is necessary to use as many indices as possible for better description of the egg shape, and on the other hand, a large number of indices leads to an unjustifi ed variability of the investigated sample of eggs, making it increasingly diffi cult to choose either typical characteristics for the given species, or the tendency of their variability (Narushin, 2001). The aim of presented research is to perform and combine two simple but satisfactory methods of chicken egg shape variability evaluation, namely (i) variability of SI, completed for calculated va ria bili ty of egg volume and area (based on formulas of Narushin, 2001, 2005), and (ii) shape variability determined by analytical so ware Shape 1.3 (based on elliptic Fourier descriptors and developed by Iwata and Ukai, 2002). The second method was recently applied with success for description of numerous biological shapes 70 M. Havlicek, S. Nedomova, J. Simeonovova, L. Severa, I. Křivanek (Toayohara et al., 2000; Iwata et al., 2002b; Yoshio ka et al., 2004; Yoshioka et al., 2006 and other). The method describes the entire shape mathematically through transforming coordinate information concerning its contour into Fourier coeffi cients. MATERIALS AND METHODS For the purpose of experiment, a sample of 250 fresh eggs was collected. The eggs were laid in 52nd week of age by the hens of ISA BROWN strain. Egg geometry calculated from length (L) and width (W) The lenght L of egg longitudinal axis and maximum width W were measured by digital micrometer SOMET (Germany). With regard to measurement accuracy and relevance, two decimal numbers were considered. Accurate direct measuring of egg surface represents rather diffi cult problem (Narushin, 1997b). Thus diff erent formulas using diff erent coeffi cients and values were proposed. Generally, a formula for egg surface S calculating can be expressed as