Nasarawa State University, Department of Animal Science, Nigeria
Body weight and nine morphostructural characters (withers height, rump height, heart girth, body length, head width, cannon circumference, shoulder width, rump width and rump length) of 83 Bunaji cows were used to study the problem of multicollinearity instability in the estimation of body weight from morphological traits. The animals, which were aged 1.5-2.4 years were semi-intensively managed at the Livestock Complex, College of Agriculture, Lafia, Nasarawa State, north central Nigeria. Pairwise phenotypic correlations indicated a high and positive significant relationship between body weight and body dimensions (r = 0.61-0.94; p < 0.01). Among the linear type traits, the highest correlation was observed between withers height and rump height (r =0.98) while the lowest value was recorded for rump height and shoulder width (r =0.51). Severe collinearity problems were evident in 5 of the zoometrical variables as portrayed by variance inflation factors (VIFs) higher than 10.00 (VIF = 33.096, 31.421, 24.612, 22.726 and 13.327 for rump height, withers height, rump length, heart girth and body length, respectively). Tolerance (T) values were also lower than 0.1 (T =0.030, 0.032, 0.041, 0.044 and 0.075 for rump height, withers height, rump length, heart girth and body length respectively). Collinearity problems were further confirmed from the computations of the Eigenvalues of the correlation matrix, condition indexes and variance proportions. Heart girth was retained among the collinear variables, and singly accounted for 87.9% of the variation in body weight. From the stepwise regression model, body weight was best predicted from a combination of heart girth, cannon circumference and shoulder width.
Keywords: Body measurement, body weight, Bunaji cow, multicollinearity, stepwise regression