# Ultrasound Back-Fat Thickness Association with Risk of Metabolic Disease of Dairy Cows in Early Lactation

## TL;DR

Ultrasound back-fat thickness can predict the risk of metabolic disease in dairy cows during early lactation.

## Contribution

Ultrasound back-fat thickness is shown to be a more reliable indicator of hyperketonemia risk than body condition score.

## Key findings

- Back-fat thickness loss of 1 mm is associated with increased risk of hyperketonemia.
- Weekly changes in back-fat thickness are easier to detect than changes in body condition score.
- Higher initial back-fat thickness correlates with higher risk of developing hyperketonemia.

## Abstract

Subclinical ketosis or hyperketonemia can significantly impact animals’ health. The body condition score is a subjective method associated with hyperketonemia. On the contrary, ultrasound measurements of back fat thickness are an objective method that could assess the risk of metabolic disease. A total of 129 multiparous dairy cows were followed weekly during the first 8 weeks after calving with both methods and checked for hyperketonemia. Two groups were established retrospectively: control or healthy animals (n = 73), and diseased animals (n = 56). Our results showed that the body-condition score and back-fat thickness were strongly related. Moreover, animals with greater body-condition score or back-fat thickness at the beginning of lactation had a higher risk of developing hyperketonemia as well as animals with greater losses over the postpartum period. Moreover, the risk of developing hyperketonemia was greater with 1 point of body-condition score loss compared to the loss of 1 mm of back-fact thickness. However, the results suggest that the decrease in back-fat thickness could be easily identified over weeks contrasting with body-condition score. In conclusion, the back-fat thickness could represent a useful method to assess the hyperketonemia risk during the postpartum period.

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 (TotalΔ8to1BCS, TotalΔ8to1BFT, TotalΔ8to1BHB). 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.