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The overall aim of this thesis was to improve the on-farm diagnosis of subclinical ketosis pre- and postpartum and to gain further knowledge about the effects and classification of subclinical ketosis within the first six weeks of lactation. To evaluate the metabolic situation of dairy herds and to detect affected cows, the measurement of non-esterified fatty acids (NEFA) and ß-hydroxybutyrate (BHBA) was shown to be a useful diagnostic tool. Circulating concentrations of NEFA and BHBA measure aspects of the success in adaptation to a state of negative energy balance.
Prepartum measurement of NEFA on-farm would be a useful alternative to laboratory analysis, however, hand-held devices for the measurement of NEFA are not available yet. Therefore, the aim of the first study was to evaluate if different parameters of fat metabolism could serve as surrogates for NEFA. Specifically, it was determined if it is feasible to predict the concentration of NEFA by the measurement of BHBA, cholesterol, triglycerides (TAG) and HDL as surrogates. A total of 254 cows were included in the trial. One blood sample was taken from each cow between d 10 and d 1 prepartum. Second and third samples were collected on d 2 and d 10 postpartum, respectively. The coefficients of correlation between parameters were calculated and a receiver-operator characteristic curve analysis was conducted. The prediction of NEFA concentrations using only one of the parameters was insufficient. However, a NEFA concentration ≥ 0.5 mEq/L could be predicted with a high sensitivity (i.e., Se = 0.88) and specificity (i.e., Sp = 0.93) from d 3 to d 1 prepartum and a NEFA concentration ≥ 0.7 mEq/L could be reliably predicted on d 2 postpartum (i.e., AUC = 0.89, Se = 0.89, Sp = 0.76) when using a combination of BHBA, cholesterol and TAG as surrogates. Overall, the results suggest that a combination of different parameters of lipid metabolism could be used as surrogates for NEFA. However, hand-held devices for cholesterol and TAG would have to be evaluated for the usage in cows before this method could be used in practice.
Postpartum the measurement of blood BHBA is a common tool for on-farm diagnosis of subclinical ketosis. Some authors speculated that there are two different types of ketosis differing in their onset and pathophysiology. According to that theory type I ketosis, the spontaneous type, occurs 3 to 6 weeks postpartum, whereas type II ketosis, known as “fat cow syndrome” occurs in week 1 to 2 postpartum. Several studies evaluated the effects of hyperketonemia within the first 2 weeks after parturition. However, there is no evidence if hyperketonemia occurring in week 3 to 6 of lactation has the same impact on health and production as the early type. Therefore, the aim of the second study was to evaluate the effects of hyperketonemia on milk production (1st test day milk yield and 100 DIM milk yield), reproductive performance (time to first service, first service conception risk, and time to pregnancy within 200 DIM) and early lactation culling risk within the first six weeks of lactation. A total of 655 Holstein 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 BHBA for an examination period of 42 days resulting in 12 test results per cow. Hyperketonemia was defined as a BHBA concentration ≥ 1.2 mmol/l. The onset of hyperketonemia was described as early onset (first hyperketonemia event within the first 2 weeks postpartum) and late onset (first hyperketonemia event in week 3 to 6 postpartum). Prevalence and incidence of hyperketonemia were assessed based on the 12 examinations. Cumulative incidence of hyperketonemia was 48% and 72% for primiparous and multiparous cows, respectively. Mean prevalence was 17.5%. Early onset ketotic cows had a higher 1st test day milk yield (+ 3.0 kg/d, P < 0.001) and 100 DIM milk production (+ 301.6 kg; P < 0.001) compared to non-ketotic cows. There was no effect of late onset of ketosis on milk production. There were no effects of hyperketonemia on reproductive performance and culling risk, irrespective of onset of ketosis.
In order to further investigate the hypothesis of type I and II ketosis a third study was conducted to evaluate the associations between hyperketonemia and hypoglycemia in early lactation. According to the theory of type I and II ketosis, early onset ketosis (week 1 to 2 postpartum) is the hyperglycaemic-hyperinsulinaemic form whereas late onset ketosis (week 3 to 6 postpartum) is the hypoglycaemic-hypoinsulinaemic form. A total of 655 dairy cows from 6 commercial dairy farms in Germany were enrolled between 1 and 4 days in milk (DIM). Cows were tested twice weekly for 6 weeks using an electronic handheld meter for glucose and BHBA, respectively. Hypoglycemia was defined as glucose concentration ≤ 2.2 mmol/L. Hyperketonemia was defined as a BHBA concentration ≥ 1.2 mmol/l. As described above, the onset of hyperketonemia was described as early onset (first HYK event within the first 2 weeks postpartum) and late onset (first HYK event in week 3 to 6 postpartum). The effect of ketosis status on blood glucose within 42 DIM was evaluated using a generalized linear mixed model. There was no effect of HYK on glucose concentration in primiparous cows (P > 0.1). Multiparous cows with early onset HYK had a lower glucose concentration (-0.21 mmol/L) compared to non-ketotic cows (P = 0.041). Unlike the theory of type I and II ketosis, hypoglycemia was not associated with late onset HYK but with early onset HYK. Overall, primiparous cows had a lower prevalence and incidence of hypoglycemia than multiparous cows. Hypoglycemia in multiparous cows was associated with higher 1st test day milk production and 100 DIM milk production. In conclusion, hypoglycemia mainly occurred in multiparous cows with early onset HYK whereas primiparous were at a lower risk for hypoglycemia, presumably due to their lower metabolic load.