The effect of maternally derived immunoglobulin G on the risk of respiratory disease in heifers during the first 3 months of life.

The objectives were to investigate the association between postcolostral serum IgG and the development of calf pneumonia, to elaborate the risk factors for pneumonia, and to compare the risk factors for clinician- and caregiver-diagnosed respiratory disease. In a prospective observational cohort study, 410 heifer calves were clinically examined weekly by a veterinarian during their first 3 months of life. With an initial questionnaire and during these weekly visits, management data were collected. A nested matched case-control design was used to compare risk factors between 105 calves with respiratory disease and their 59 control calves from the same initial population. The IgG levels were determined from blood samples taken within 2 weeks after colostrum intake. The appropriate cutoff point for the postcolostral IgG level to indicate failure of passive antibody transfer when predicting pneumonia appeared to be between 800 and 1300 mg/dl (values < or = the cutoff point indicated failure). Calves with low IgG levels had 2-times higher odds of pneumonia than calves with higher IgG concentrations. Housing mostly in the presence of adult cattle was a risk factor for pneumonia, whereas housing mostly alone in a hutch was protective. Feeding of mastitic colostrum was a risk factor for clinician-diagnosed pneumonia in the analysis of the cohort study but not in the matched case-control design. There was a three-times higher risk of pneumonia if calves were given their dam's colostrum for the first feeding and the dam had clinical mastitis at the time of first milking. Caregiver- and clinician-diagnosed pneumonia had slightly different risk factors which implies that caution should be used when comparing studies based on different definitions of pneumonia. The practical implications of this study are that more attention should be paid to proper housing conditions of the calves in order to reduce incidence of pneumonia.