EXTERNAL INDICATION AGE MODELS FOR FIRST CALVING

Abstract

The results of predicting the age of the first calving using multiple regression analysis, based on exterior measurements and body structure indices of heifers, determined twice - at the age of about 100 days and about a year are shown. The models are designed using both linear and nonlinear components. The developed models are considered in terms of their adequacy and reliability. To improve the quality of the models, the "folding knife" method was tested. Verification of models was carried out by methods of sliding control, division of the sample into educational and examination samples and selection simulation. The most important dependencies are highlighted and analyzed. Based on the exterior indicators of heifers around 100 days of age, we obtained a model for predicting the age of the first calving, which was unreliable (P = 0.91) and characterized by a low reduced coefficient of determination (R2adj = 0.21) and a large standard prediction error (SE = 104.75 days). The final parameters of the model of predicting the age of the first calving based on exterior indicators determined at an age of about one year are characterized by high reliability (p> 0.999), good determination (R2adj = 0.58) and quite acceptable differences between predicted and actual values of the age at first calving (SE = 77.01 days). The most adequate is the model based on a double exterior study. It is advisable to use this model in the version of the "folding knife" for a more accurate and complete assessment of animals at an early age. This model provides a coincidence of predicted and actual negative estimates of the age of the first calving in 65.7% of cases. The most valuable features for predicting and interpreting the dependence of the age of the first calving on the exterior of heifers are such as the stretch index and oblique body length at 365 days of age. The degree of their influence on the expected age of the first calving is the maximum among all predictors and is η2=16.46% and η2=9.10%, respectively.