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Factors associated with morbidity in dairy heifer calves on U.S. dairy operations
The objective of this study was to evaluate morbidity in U.S. dairy heifer calves based on different health, feeding, and management practices, as well as environmental factors. This study was conducted as part of the calf component of the National Animal Health Monitoring System’s Dairy 2014 study, which included 104 dairy operations in 13 states. The calf component was an 18-mo longitudinal study focused on dairy heifer calves from birth to weaning; data were collected on 2,545 calves. The morbidity rate for all calves enrolled in the study was 34%, with 7% of calves experiencing more than one disease event. It is likely that some sick calves were neither identified nor recorded and morbidity is underreported. The majority of clinical signs reported were digestive (56%) and respiratory (34%). Almost all sick calves (90%) received treatment, with 81% of treated calves receiving antimicrobials. Of calves treated with antimicrobials, the most commonly used classes were fluoroquinolones (28% of calves) and sulfonamides (25% of calves). The mortality rate for the study was 5.2%. The primary causes of death were reported as unknown (35% of calves), digestive (31%), and respiratory (16%). Backward elimination model selection in Proc Genmod of SAS® was used after univariate screening (P <0.2) to determine which environmental factors and management practices significantly impacted morbidity. The final model included serum IgG (P = 0.024), gender of the primary caretaker (P = 0.031), and number of calves housed together (P = 0.049). Calves with an increased serum IgG were less likely to have a reported a disease event. Calves that had a female or male as the primary caretaker were 1.2 times more likely to have a reported disease event compared with calves that had a male and female as the primary caretaker. As group size increased, the risk of reported disease also increased. Practices that weren’t significant in the final model included the use of vaccines, the addition of antibiotics, coccidiostats, or direct fed microbials to milk, and pasteurization of milk. These results highlight the continued importance of ensuring a high level of passive transfer of immunoglobulins in calves via colostrum, the importance of vigilant caretakers, and the possible morbidity risks of group housing.
Keywords: dairy heifers; morbidity; mortality