DETERMINATION OF NON-GENETIC FACTORS INFLUENCING BIRTH WEIGHT USING REGRESSION TREE METHOD IN BROWN-SWISS CATTLE

Abstract

The aim of this study was to determine the influence of non-genetic factors on the birth weight of Brown-Swiss calves, maintained at Sultansuyu State Farm (lat. 380 E, long. 380 N, and 981 m above sea level) of Malatya province in the Eastern Anatolia Region of Turkey during the years 1984-2010. Data on birth weight, calving season, calf sex, and calving year were collected from 3168 Brown Swiss calves. The data were exposed to regression tree method, which is a tree-based and a non-parametric method. In this method, birth weight, an important trait in cattle breeding, was a response variable and environmental factors such as calf sex, calving season and year were accepted as explanatory variables. Statistical evaluations were done using SPSS (Exhaustive CHAID) statistical package program. In the present study, birth year was the most significant factor for birth weight (P<0.01), followed by sex (P<0.01) and calving season (P<0.01). The highest average birth weight was recorded for the calves born during the years 1999-2001. The calves born in summer and fall seasons of 2002-2004 years were lighter than those born in winter and spring seasons of same years. Sex of calf influenced birth weight of calves born between the years 1991 and 1995 (P<0.01). Among factors, calving season was a factor that had highly statistical influence on birth weight of the group of calves born between 2002 and 2004 years. As a result, use of regression tree method, which is not influenced by multicollinearity, outlier, and missing values is recommended with the objective to identify factors that can be statistically significant on birth weight of Brown Swiss calves.