| Summary: | The main objective of the present study was to evaluate the beta-hydroxybutyrate (BHB) and fat to protein content (F:P) ratio patterns in the milk of Holstein cows with postpartum diseases throughout the first five months of lactation. This prospective study was performed at Vestjyske Dyrlaeger ApS (Nørre Nebel, Denmark). The milk fat, protein, and BHB were evaluated in the Danish Eurofins laboratory according to the monthly averaged days in milk (DIM1 to 5). According to clinical records, five groups were formed: A (control group; cows without diseases; <i>n</i> = 32), B (cows with left displaced abomasum -LDA- and concomitant diseases; <i>n</i> = 25); C (cows with other diseases up to DIM3; <i>n</i> = 13); D (cows with foot disorders up to DIM3; <i>n</i> = 26); and E (cows with disease manifestations in DIM4 and DIM5; <i>n</i> = 26). All the sick cows were treated after diagnosis, and laparoscopy was performed on cows with LDA. In group B, a higher concentration of BHB (0.18 ± 0.02 mmol/L; <i>p</i> < 0.001) was observed than in the control group (0.07 ± 0.02 mmol/L; <i>p</i> < 0.001) in DIM1, presenting an odds ratio (OR) = 8.9. In all groups, BHB decreased to 0.03–0.05 mmol/L (<i>p</i> < 0.05) since DIM3. The F:P ratio was higher in group B (1.77 ± 0.07) than in group A (1.32 ± 0.06; <i>p</i> < 0.05) in DIM1. A similar profile is observed in DIM2. It was observed that animals in group B were four to six times more likely to have a F:P ratio ≥1.29 during DIM1 (OR = 4.0; 95% CI:1.3–14.4; <i>p</i> = 0.01) and DIM2 (OR = 5.9; 95% CI %:1.9–21.9; <i>p</i> < 0.01), than cows in group A. There were also moderate and high correlations between the F:P ratio and the BHB for DIM1 (r = 0.57; r<sup>2</sup> = 0.33; RSD = 0.09; <i>p</i> < 0.001) and DIM2 (r = 0.78; r<sup>2</sup> = 0.60; RSD = 0.07; <i>p</i> < 0.001), respectively. We concluded that animals affected by LDA in the postpartum period have a higher concentration of BHB in milk in DIM1 and all treated animals quickly recover BHB levels up to DIM3. The F:P ratio is a viable and economic indicator, mainly in DIM1 and DIM2, to estimate BHB concentration and energy balance in cows with LDA and other postpartum diseases.
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