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Introduction
Early identification of disease in calves is important to ensure good welfare, and because their health status can affect subsequent growth and productivity. 1 Clinical scoring systems in calves have been proposed as an approach to systematic screening for early disease to improve calf health and survival. 2 3 The most prevalent and economically important calf diseases are diarrhoea 4 and respiratory disease 5 which form major components of calf scoring approaches. Detecting disease like calf pneumonia and grading its severity is challenging. 6-8 One study found that stock people detected just 56 per cent of clinical pneumonia cases. 9 Furthermore, agreement between veterinarians for identifying clinical illness in calves has also been reported as poor. 6 Successful treatment of diseased calves, regardless of aetiology, is likely to be determined by the speed of disease detection and treatment, although evidence is sparse on this subject. While the rationale for regular calf scoring is clear, there are few studies evaluating its performance and relationship with calf health parameters.
Disease in preweaned calves has a negative influence on performance later in life. 10 Production of replacement dairy heifers can account for 20 per cent of farm expenses 11 with losses due to disease and death representing a major source of inefficiency. 12 The aim of this study was to investigate whether detection and treatment of disease through the use of a modified Wisconsin calf disease scoring system decreased the impact of disease on future performance as assessed through mortality rates, age at conception and 305-day milk yield. It is hypothesised that preweaned calves with poor clinical scores will perform less well, and have higher mortality rates than their 'healthier' counterparts.
Materials and methods
Study period and farm management
A longitudinal cohort study was conducted on a 360-cow dairy farm in Dorset, UK, from August 2011 through December 2015. The average 305-day yield was 9434 litres, with cows housed in deep sand cubicles and fed a total mixed ration during the winter. In summer, cows were on pasture grazing grass and had a buffer feed. Cows were milked twice daily. All youngstock were homebred during the study period. Newborn calves were separated from their dam as soon as possible after birth with a maximum interval of 12hours...