Abstract
Ultrasound back-fat thickness (BFT) can indirectly assess the risk of metabolic disease as hyperketonemia. In this study, 129 multiparous and clinically healthy dairy cows were enrolled and examined weekly for the first 8 weeks of lactation for body-condition score (BCS), BFT, β-hydroxybutyrate (BHB), weekly changes (ΔBCS, ΔBFT, ΔBHB), and total changes over the study (TotalΔ(8to1)BCS, TotalΔ(8to1)BFT, TotalΔ(8to1)BHB). Cows with BHB ≥ 1.0 mmol/L were considered to be affected by hyperketonemia (HK; n = 56), while the remaining animals were considered as controls (CTR; n = 73). Statistical analysis included mixed models, spearman correlation matrix, logistic regression, and linear regression analysis. BCS and BFT showed a strong correlation and were greater in the first weeks after calving in HK. The same group had greater BCS and BFT losses over the trial. However, weekly changes were identified only for BFT. Linear and logistic regression analysis for the disease event identified that BFT loss of 1 mm was associated with an increase in BHB (+0.36 mmol/L) and an increased risk of developing hyperketonemia over the week when the loss was between the second and first weeks (+2.5 times), third and second (+51%), and fourth and third (+58%) weeks. In conclusion, BFT can be used to identify the risk of developing hyperketonemia during early lactation.