Prevalence of increased milk BHB and its association with SCC and milk components

The aim of this study was to investigate the prevalence of subclinical ketosis in dairy cows based on elevated levels of milk β-hydroxybutyrate (BHB), somatic cell count (SCC), and oth¬er milk components. The analyzed data were obtained through routine analyses Dairy Herd Improvement (DHI) milk samples, by Fourier-transform infrared (FTIR) spectroscopy. The initial dataset included a total of 23,492 Holstein cow milk samples collected between January 2022 and January 2025 on six farms located in the Province of Vojvodina, Serbia. After outlier removal, final data set included 22,915 milk samples. Based on the concentration of β-hydroxy¬butyrate (BHB), 75 % of the samples were in the first negative group (BHB<0.10 mmol/L), with an average concentration of 0.03 mmol/L. The second, suspicious-negative group (BHB 0.11- 0.15 mmol/L) comprised 15 % of the samples, with an average of 0.13 mmol/L. In addition, 6 % of the samples fell into the third, suspicious-positive group (BHB 0.16-0.20 mmol/L), with an average of 0.18 mmol/L, while the fourth, positive group (BHB>0.20 mmol/L) comprised 4 % of the samples, with an average concentration of 0.34 mmol/L. Through the analysis of the milk components, it was determined that in the first period, at 5-42 days in milk (DIM), significantly affected all observed parameters. The lactose content is decreasing, while fat, protein, total solids, milk fat/protein (F/P) ratio, SCC and urea are increasing. The results highlight the potential of using milk samples from Dairy Herd Improvement (DHI) programs to monitor elevated levels of milk BHB and SCC at the herd level. This approach may serve as a useful tool for estimating the prevalence of subclinical ketosis in dairy cows. Additionally, different BHB thresholds might be needed for different periods of lactation.