On the relationship between lactational performance and health: Is it yield or metabolic imbalance that cause production diseases in dairy cattle? A position paper

The objective of this review was to explore the relationship between lactational performance and health. We focused on lactational incidence rates (LIR) of the production diseases that are of economic importance to the dairy industry. Based on a review of 11 epidemiological and 14 genetic studies we found little evidence that high yielding cows have increased risk of dystocia, retained placenta, metritis and left-displaced abomasum. Results for periparturient paresis were inconsistent. Whilst we found no phenotypical relationship between milk yield and the risk of ketosis and lameness, selection for higher milk yields will probably increase LIR for these diseases. Mastitis was the only disease where there was a clear relationship between milk yield and risk of infection. Continued selection for higher milk yields will worsen this situation. However, our overall conclusion is that reviewing existing literature, even with a structured literature selection, is inadequate to the task of elucidating the relationship between lactational performance and risk of production diseases. There are substantial problems with confounding effects and unaccounted for biological correlations. In the second part of the review we argue towards a common basis for addressing production diseases. We propose abnormal body mobilisation and immune competence as common currencies for metabolic and immune status and argue for the development of indicators of metabolic imbalance and the early development of diseases. Furthermore, we suggest the use of indicators of ‘imbalance’ to guide feeding according to the needs of individual cows with their specific genotype and management history. We believe that this approach has the potential to provide new diagnostic and decision support tools to improve animal health and reproduction, whilst simultaneously maintaining optimal production and efficiency. Further research is needed to identify and validate new indicators and individual feeding strategies.