Methods for estimating body reserves in grazing dairy cows: Body condition score and backfat thickness

Objective: The aim of this study was to evaluate whether the changes of backfat thickness (BFT) measurements throughout the lactation of cows in a grazing-based dairy farm in southern Brazil are reliably detected as changes in visual BCS. Materials and Methods: Paired measurements of BCS and BFT were taken monthly throughout 12 mo in 152 Holstein cows (585 +/- 63 kg of BW; 18 +/- 4.5 kg of milk/d; 113 +/- 76 DIM) in a commercial herd in southern Brazil. The diets consisted of grazing tropical or temperate pastures, supplemented with additional feedstuffs. The changes of body condition throughout the lactation and month of experiment were identified, and linear regression analysis was performed between values of BCS and BFT. Results and Discussion: In general, both BCS and BFT were not affected by month of year, although there was a reduction of both BCS and BFT in January compared with December (P < 0.05). A significant increase in relative variation of both BCS and BFT (P < 0.05) was detected only from mo 2 to 3 of lactation. However, the mean BFT values showed greater variability than those of BCS throughout lactation. The linear relationship between BCS and BFT measurements was as follows: BFT (mm) = 4.29BCS + 5.17 (root mean squared error = 2.88; P < 0.01; n = 669). Implications and Applications: The change in BFT of cows was not precisely detected as a change in their BCS. However, the average variability of herd body condition, as detected by BFT, was also detected by BCS, and thus, either tool is acceptable to be used by farmers.