Application of Classification Tree Method to Determine Factors Affecting Fertility in Japanese quail Eggs

The aim of this study was to determine the effects of genotype, season and cage stocking density on fertility in Japanese quail using Classification Tree Method (CTM). CTM visually displays valuable information about the relations between independent variables in large data sets in the form of a tree diagram. The material of this study were 1954 hatching eggs from a selected a line (S line) and a randomly coupled control group (C line); the eggs were collected in three different seasons (spring, summer and autumn) and the quails were bred in two different stocking densities (160 and 240 cm2/bird). For CTM analysis, fertility was used as the dependent variable and genotype, season and cage stocking density were used as independent variables. The effects of all three factors on fertility were found significant with season exerting the highest effect followed by stocking density and genotype (P < 0.05). While the lowest fertility ratio (63.91 %) was observed with S line bred in summer at a stocking density of 160 cm2/bird, the highest fertility ratio was observed with C line bred in autumn at a stocking density of 240 cm2/bird. A significant difference in terms of stocking density and genotype was found in summer and autumn. According to the CTM analysis results, the high temperatures in summer caused heat stress and had negative effects on fertility; this effect was even stronger on quails that had been selected for increased living weight and were kept at a stocking density of 160 cm2/bird.