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This study aimed to assess the effect of ketone body status early postpartum on time empty in 74 multiparous dairy cows under field conditions. Animals were equally distributed across eight farms and were controlled by the same herd-fertility-monitoring programme. Cows were visited twice antepartum and six times postpartum at weekly intervals between 0530 and 0830 a.m. On these occasions, body condition scores and milk yields were measured, blood and milk samples were taken, cows were gynaecologically examined, and parameters of reproduction were recorded. Cows with a time empty of less or more than 80 days were classified as early and late conceiving cows (EC and LC, respectively). A time empty of 80 days results in calving-to-calving intervals of 1 year and classification based on this threshold value resulted in groups of equal size and equal distribution of EC and LC within farms. Ketone bodies measured were beta-hydroxybutyrate in blood and acetoacetate and acetone in blood and milk. Blood and milk ketone body concentrations, as well as the ratios of acetoacetate and acetone to beta-hydroxybutyrate, over the first 6 weeks postpartum were higher in LC than in EC, whereas plasma glucose and non-esterified fatty acids and milk fat, protein and urea concentrations did not exhibit clear differences between groups. Ketone body concentrations were as good predictors of time empty as ketone body ratios and might have practical impact in herd-fertility-monitoring programmes.

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