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Objectives: The first 2 weeks after calving have been described as the main risk period for hyperketonemia (HYK). However, it was recently shown that dairy cows continued to be at risk for HYK until at least 42 DIM. The objectives of our study were to describe the epidemiology of HYK within the first six weeks of lactation and to evaluate the effects of HYK on milk production, reproductive performance and early lactation culling risk.
Materials and Methods: A total of 662 dairy cows from 6 commercial dairy farms in Germany were enrolled between 1 and 4 DIM. Cows were tested twice weekly using an electronic handheld meter for β-hydroxybutyric acid (BHBA) and glucose for an examination period of 42 days resulting in 12 test results per cow. Hyperketonemia (HYK) was defined as a BHBA concentration ≥ 1.2mmol/l. The onset of HYK was described as early onset (first HYK event within the first 2 weeks) and late onset (first HYK event in week 3 to 6 postpartum). Prevalence and incidence of HYK were calculated for the 12 examination days. The number of HYK events and time to a negative test event in HYK positive cows were described. The effects of onset of HYK within the first six weeks of lactation on milk production (1st test day milk yield and 100 DIM milk yield), reproductive performance (time to first service and first service conception risk), and on early lactation culling risk were analyzed separately using a GENLINMIXED procedure.
Results: Cumulative incidence of HYK was 47% and 69% for primiparous and multiparous cows, respectively. Multiparous cows had a higher incidence and prevalence of HYK within the first six weeks of lactation than primiparous cows. The peak incidence was found in the first week of lactation and decreased steadily within the first six weeks of lactation. Prevalence stayed on the same level within the first six weeks of lactation. About 20% of all cows had one event of HYK within the first six weeks of lactation. Less than 5% of all cows had 6 or more HYK events. About 70% of HYK positive cows had a negative test result from one test to another 3 to 4 days later after the initial diagnosis of HYK. Cows with early onset of ketosis had a higher 1st test day milk yield (+2.3 kg/d, P = 0.002) and 100 DIM milk production (+287 kg; P < 0.001) compared to nonketotic cows. There was no effect of late onset of ketosis on 1st test day milk yield and 100 DIM milk production. There was no effect of HYK on time to 1st service, irrespective of onset of ketosis and no effect of HYK on first service conception risk, irrespective of onset of ketosis. Cows with late onset of HYK had a decreased culling risk (HR = 0.365; P = 0.045) compared to non-ketotic cows. The culling risk of cows with early onset of ketosis was comparable to non-ketotic cows (HR = 1.447; P = 0.212).
Conclusions: The risk period for HYK lasted at least until lactation week 6. However, a high number of HYK positive cows had a negative test result after the initial diagnosis of HYK. Cows with early onset of HYK had higher milk production compared to non-ketotic cows. HYK was not associated with negative effects on reproduction and early lactation culling risk. HYK in early lactation seems to be part of a physiological adaptational response to negative nutrient balance in transition dairy cows.