DESCRIPTIVE EPIDEMIOLOGY OF MORBIDITY AND MORTALITY IN MINNESOTA DAIRY HEIFER CALVES

A prospective study was carried out on 845 heifer calves born during 1 991 on 30 Holstein dairy Farms in southeast Minnesota. The objectives of the study were to describe the epidemiology of morbidity and mortal ity in dairy calves from birth to 16 weeks of age (with an emphasis on respiratory disease), to examine individual calf and herd management practices as risk factors for calf morbidity and mortality, and to val idate producer diagnosis of mortality. Incidence rates for all morbidi ty, enteritis, and pneumonia were 0.20, 0.15, and 0.10 cases per 100 c alf-days at risk for the period of the study. Risk of enteritis was hi ghest in the first 3 weeks of life, with pneumonia risk highest at 10 weeks of age. Case fatality rates averaged 11.8%, 17.9%, and 9.4% for all diagnoses, enteritis, and pneumonia, respectively. Average daily r ates of gain from birth to 16 weeks of age differed between farms that had inadequate calf housing (0.8 kg day(-1)) versus those with adequa te calf housing (1.0 kg day(-1)). Approximately half of the calves in the cohort (418) had blood samples taken monthly from birth until 16 w eeks of age. Of the calves sampled, only 19 calves showed a four-fold rise in serum titers to respiratory viruses. Sixteen calves seroconver ted to BVDV, two calves to IBRV, and one calf to PI3 virus. Of 98 calv es less than 10 days of age tested for adequacy of passive transfer, 3 5 (35.7%) had serum immunoglobulin levels of less than 800 mg dl(-1). There were no significant differences in mortality or morbidity betwee n calves that had adequate passive transfer and those that did not. Th e incidence of mortality was 0.08 deaths per 100 calf-days at risk; 64 calves died during the 16 months of the study. The risk of death was highest at 2 weeks of age. Enteritis was the most common cause of deat h (28 deaths, 44% of all deaths) followed by pneumonia (19 deaths, 30% of all deaths). Comparing producer diagnosis of mortality with necrop sy results yielded sensitivities of 58.3% and 56% and specificities of 93% and 100% for producer diagnoses of enteritis and pneumonia, respe ctively. The kappa statistic comparing producer diagnosis with necrops y result was 0.47. The most common pathogens isolated from calves that died of enteritis were rotavirus (five calves), and Escherichia coli (four calves), Pathogens isolated from pneumonic lungs included Pasteu rella multocida (three calves), Haemophilus somnus (three calves), and Pasteurella haemolytica (one calf).