Rates and risk factors for contagious disease and mortality in young dairy heifers.

Abstract

Abstract Dairy heifers, particularly when <3 months, are at high risk for mortality and morbidity. Accurate data are lacking because of poor recording on farm, difficulties over disease diagnosis and potential bias of farm selection. Mortality during rearing varied from 6 to 14% between studies. The range from 0 to 30% on individual farms suggested that deaths are preventable with good husbandry. Contagious disease was the major cause of mortality at <6 months, with trauma, accidents and infertility more important in older animals. Bovine respiratory disease (BRD) and diarrhoea were the most common diseases. Both are endemic, low-mortality and high-morbidity conditions. The prevalence of diarrhoea was 19-35%, with higher incidences during disease outbreaks. Cryptosporidium parvum and rotavirus were the dominant pathogens. The causative pathogens for BRD were harder to identify, with large differences between levels of farmer- and veterinarian-diagnosed disease and higher incidences in North America (around 16%) than Europe (around 3%). Analysis of the risk factors for disease and mortality highlighted that closed herds, good hygiene and availability of roughage were consistently associated with improved outcomes. Some common practices were challenged by the results of large, prospective studies. Calf diarrhoea was only weakly associated with good passive transfer of immunity via colostrum, suggesting other control strategies are required. Morbidity with small group housing demonstrated no disadvantages compared with contiguous single pens, so this system should be encouraged to improve welfare. Routine use of antibiotics in calf diarrhoea was associated with negative outcomes, so is actively discouraged.