Relationship between body mass and empty body mass in growing goats

The accuracy of body mass assessment is largely affected by gastrointestinal tract (GIT) content, then the use of empty body mass (EBM) instead of body mass (BM) may reduce the variation of estimates. The objective of this study was to develop statistical models to predict EBM by BM, testing the influence of sex (females, intact males or castrated males), type of diet (suckling or post-weaning), and genotype (Saanen, 1/2 Boer x 1/2 Saanen; 3/4 Boer x 1/4 Saanen or indigenous goats). Individual records of 311 goats with BM ranging from 4.3 to 47.4 kg were combined from 10 studies. The EBM was computed as the BM at slaughter minus mass of GIT content, bladder, and gallbladder. Linear regression analyses were performed to develop the models, considering sex, diet type and genotype as fixed effects and random effect of study. The variance due to study was considered using the RANDOM statement of MIXED procedure. CONTRAST statements were used to conduct all pairwise comparisons of fixed effects and all the statistical analyses were performed using SAS. Sex did not affect both intercept (P = 0.53) and slope (P = 0.19). On the other hand, EBW prediction was affected by type of diet (P < 0.01), and genotype (P = 0.02). Therefore, different equations were proposed to predict EBW from BW for suckling (EBW_suckling = 0.714 (? 0.351) + 0.742 (? 0.032) x BW) and post-weaning Saanen goats (EBW_post-weaning = - 0.608 (? 0.305) + 0.841 (? 0.0093) x BW). In general, GIT content (g/kg EBM) in suckling goat kids increased as they grew, oppositely it remained slightly constant in post-weaning goats. The effect of genotype on the relationship between EBM and BM was tested considering only post-weaning goats, and one equation was proposed for each genotype. In general, GIT content (g/kg EBM) decreased as goat kids grew in all genotypes but indigenous goats. The results also highlighted different gastrointestinal relative capacity between genotypes.