2017 Volume 53 Issue 2 Pages 63-68
A mathematical equation for estimating the body weight of Japanese Saanen goats was developed using heart girth and body length. Body weight (W; kg), heart girth (G; m), body length (L; m), sex and age of 397 goats, including castrated, buck, goatling, pregnant, lactating and dry ones, were measured at 6, 12 and 24 months of age, and data on a total of 595 animals were collected for regression analysis. Three-fourths of the goats were randomly selected from each stratum made by sex and age, and data from those goats were used for training (or learning) data (456 animals) and the data from the remaining goats were used for test data (139 animals). In addition, 451 goats excluding abnormal values (5 animals) of the training data were used for basic data. Three regression models were constructed based on the basic data (451 goats). The first model employed G2L as the only explanatory variable, the second model sex, age and G2L, and the third model was obtained by applying a stepwise forward model selection technique to two potential explanatory variables, G and L. Correlation coefficients between predicted and observed values of W and residual standard deviation (RSD) were used for comparison measures. Those measures for each model were computed using the test data (139 goats). Equation (1) W = 89.96G2L + 2.29 was selected as the best model with the correlation coefficient 0.960 and RSD 4.450. The other two models were expressed as follows: (2) W = 80.65G2L - 1.43sex + 0.28age + 4.38 (r = 0.964, RSD = 4.243) and (3) W = 135.24G + 30.52L - 83.72 (r = 0.958, RSD = 4.605). The fact that it is simple, has a high correlation coefficient, and was selected based on test data that were independent of training data, indicates that the estimate of the body weight obtained from a new goat is highly reliable. It is concluded that the above simple equation (1) is useful for estimating the body weight of Japanese Saanen goats.
