Validation of body condition score based on subcutaneous fat thickness measurements in primiparous Gyr cows

Context. The body condition score (BCS) is an easily measured, fast, inexpensive, and non-invasive tool to estimate the amount of body fat and to evaluate the nutritional status of dairy cows. Aims The aim of this study was to validate BCS in primiparous Gyr cows by using ultrasound measurements of subcutaneous fat (FT). Methods Body weight, BCS (score of 1-9) and FT measured at five body sites (FT1-FT5) were recorded during the prepartum and postpartum periods. Linear regression of FT on BCS and Pearson's correlations were used. Key results. The correlations between body weight and FT measures ranged from 0.49 to 0.63 and from 0.51 to 0.64 during the pre- and postpartum periods respectively, while the correlations between BCS and FT ranged from 0.69 to 0.82 and from 0.67 to 0.78 in the two periods. The BCS better reflected the variation in FT before and after calving than did body weight. Linear regression models were used to explore the relationship between BCS and FT measurements considering the former as the predictor variable. The coefficients of determination (R-2) obtained for the prepartum variables ranged from 0.48 to 0.67. The highest R-2 was obtained for the model that included FT measured in the lumbar region midway between the last rib and tuber coxae (hook; FT4) as the response variable. The R-2 of the models whose response variables were obtained during the postpartum period ranged from 0.45 to 0.60. The highest R-2 was observed when the pelvic region midway between the tuber coxae (hook) and tuber ischii (pin; FT2) was used as a response variable. Conclusions. The correlations between BCS and FT validate the use of BCS obtained by visual assessment as a tool for evaluating fat reserves in Gyr dams before calving and during first lactation. Among the FT measurements, FT2 and FT4 are interesting because both are easy to measure and showed higher correlations and coefficients of determination with BCS before calving and lactation. Implications The BCS is an accessible tool for producers that requires only training of the evaluator and that is economically viable since no special equipment is needed.