Associating milk β-hydroxybutyrate dynamics in early lactation with milk production of dairy cows

Hyperketonemia is a common problem in transition cows. However, the association between hyperketonemia and milk yield is ambiguous. In this study, we investigated the association between automatically measured milk β-hydroxybutyrate (mBHB) dynamics in early lactation and milk yield. The data was collected from 32 herds equipped with automatic milking systems. We used Generalized Additive Mixed Models to model the association between mBHB concentration and concurrent milk yield (i.e., milk yield recorded on the same day as mBHB measurement) during DIM 1-60. An increase in mBHB concentration was associated with a decrease in concurrent milk yield, but this relationship was nonlinear. Concurrent milk yield did not decline when the mBHB concentration was approximately below 0.08 mmol/L, declined gradually at elevated mBHB concentration ranging from 0.08 to 0.6 mmol/L, and then declined more steeply as mBHB concentration increased to approximately 0.6-1.0 mmol/L before plateauing. The concurrent milk yield loss ranged from 0.1 to 0.3 kg per day at an mBHB concentration of 0.1 mmol/L, and from 1.4 to 2 kg per day at an mBHB concentration of 0.2 mmol/L. Higher mBHB concentrations were more strongly associated with concurrent milk yield loss at early DIM, particularly on DIM 1 and 7. In the second analysis, we used k-medoids to cluster cows based on their degree of hyperketonemia and onset. Four hyperketonemia clusters were identified: 'non-hyperketonemia', 'early-onset moderate hyperketonemia', 'late-onset moderate hyperketonemia' and 'persistently marked hyperketonemia'. Cows in the hyperketonemia clusters had a higher 305-d milk yield than those in the non-hyperketonemia cluster. These results suggest that high mBHB concentrations are associated with concurrent milk yield loss during early lactation, particularly at early onset (DIM 1-7). However, high mBHB concentrations are positively associated with 305-d milk yield. The association between hyperketonemia and milk yield depends on both the onset and the severity. The findings highlight the importance of early sampling in the first week, as hyperketonemia during this period has the strongest influence on concurrent and potentially long-term milk yield.