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Identification of combinations of influential rearing practices applied during the heifers’ whole life on the carcass quality by the decision tree method

Abstract : The European beef farmers' income is directly related to the carcass properties according to the EUROP classification system. Several rearing practices were highlighted to influence the beef carcass properties, but most of studies was limited to one or two studied factors or to the finishing period. The aim of this study was to identify among rearing practices applied during the whole life of heifers, the combinations of practices which allowed to reach higher quality carcass properties. A classification of 636 heifers' carcasses according to their quality (carcass weight and conformation score) was performed by PCA followed by both classification methods (hierarchical cluster analysis and k-means) to select the most performant. Several methods (chi-square automatic interaction Detector, classification and regression tree and Quest) were also compared for the decision tree build. The rearing practices were collected by surveys which concerned 40 quantitative and 22 qualitative variables applied through the suckling, growth or finishing periods. The study framework included the birth season that was associated with the suckling period. The classification of the carcasses according to their quality properties identified 3 classes (Q +, Q = and Q -, n = 206, 272, 158 carcasses respectively) with a gradient of properties. The decision tree allowed the correct classification of 61.6% of carcasses of the Q + class. Among the 10 different splitters selected in the tree, the 3 life periods of the heifers were represented. Seven paths allowed to reach leaves mainly composed of carcasses of Q + class (> 50%), i.e. the class with the higher economic value, and 6 paths allowed to reach leaves mainly composed of carcasses of Q - class, i.e. the class to avoid. Two paths led to groups with 100% of carcasses of Q + class: (i) a slaughter age superior to 35.3 mo AND a pasture duration during the growth between 213 and 283 d AND a rationed distribution of grass silage in stall during the growth and (ii) a slaughter age superior to 32.1 mo AND a pasture duration during the growth between 213 and 283 d AND a lack of grass silage in stall during the growth. The rearing practices identified in the decision tree were related to the whole life of the heifers including the suckling period. These rearing practices and the associated thresholds could allow to provide advices for the production management of heifers to farmers.
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Submitted on : Tuesday, May 12, 2020 - 9:23:13 AM
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Valérie Monteils, Cécile Sibra. Identification of combinations of influential rearing practices applied during the heifers’ whole life on the carcass quality by the decision tree method. Livestock Science, Elsevier, 2019, 230, pp.103823. ⟨10.1016/j.livsci.2019.103823⟩. ⟨hal-02570405⟩

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