Abstract
Ketosis is a metabolic disorder that mainly occurs during the negative energy balance in early-lactation dairy cows. It is characterized by elevated concentrations of ketone bodies in blood (hyperketonemia), urine, and milk. The thesis of Saskia van der Drift covers investigations on etiologic factors, monitoring, treatment and genetics of dairy
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cow ketosis. Firstly, the role of the mobilization of muscle protein around parturition in the etiology of ketosis was studied. For that purpose, a method was developed to analyze the plasma concentration of 3-methylhistidine, a marker for muscle protein breakdown, by HPLC-mass spectrometry. Higher plasma 3-methylhistidine concentrations were associated with lower serum concentrations of the ketone body β-hydroxybutyrate (BHBA) in periparturient dairy cows (n = 34). This indicates that greater protein mobilization may reduce the risk to develop ketosis, probably because of a greater supply of glucogenic amino acids during negative energy balance. A large field study showed that the prevalence of ketosis (hyperketonemia) was 11.2% in early-lactation cows (n = 1678) in the Netherlands. On individual farms, the prevalence ranged from 0% to 80%. Farms participating in the study were visited on a regular test day. During these farm visits, all cows between 5 and 60 days in milk were sampled to perform the reference test for hyperketonemia (blood BHBA analysis). Data from this study were used to construct a statistical model for the routine detection of hyperketonemia at test days based on ketone body concentrations in milk (BHBA and acetone, analyzed by Fourier transform infrared spectrometry) and other available information, such as milk composition and parity. The developed model predicts the probability of hyperketonemia for each cow at the test day and subsequently estimates the prevalence of the disorder at the dairy farm. This enables routine monitoring of ketosis at test days and can contribute to the decision making on the feeding and management practices. It is common use to treat ketotic cows only when they show clinical signs, such as decreased feed intake and milk production loss. In practice, several treatment combinations are used, but evidence for the efficacy of the combined treatments was often lacking. Therefore, a clinical trial was performed with 31 cows with clinical ketosis to investigate the additive effect of a single glucocorticoid injection to oral propylene glycol treatment. Cows with clinical ketosis had a better recovery with a combined therapy of glucocorticoids and propylene glycol compared with treatment with propylene glycol only. Glucocorticoid injection resulted in higher blood glucose concentrations in ketotic cows without stimulation of muscle or fat mobilization in these animals. Finally, data from the before mentioned field study were combined with pedigree information to estimate the genetic variation and heritability of plasma BHBA, milk BHBA, and milk acetone concentrations in early-lactation cows. Heritability estimates for plasma and milk ketone body concentrations showed that variation exists in the susceptibility of cows to develop hyperketonemia and that selective breeding may contribute to a lower incidence of the disorder at the longer term
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