Factors Associated with Preweaning Morbidity, Lung Consolidation, and Mortality in Preweaned Holstein Calves in Ontario, Canada

The objective of this retrospective cohort study was to explore factors associated with neonatal calf diarrhea (NCD), bovine respiratory disease (BRD), lung consolidation (LC), and mortality on Ontario dairy farms. Health records from 2,349 Holstein calves from birth until 56 d of age across 9 dairy farms were analyzed using multivariable mixed-effects logistic regression models, which accounted for farm-level clustering through a random effect. The models evaluated associations between the outcomes of interest and season of birth, birth bodyweight, calving ease, first colostrum feeding volume, colostrum quality (measured as Brix percentage), number of colostrum feedings, time of birth, and transfer of passive immunity (TPI), using the categories of poor (<5.1 g/dL), fair (5.1-5.7 g/dL), good (5.8-6.1 g/dL), and excellent (≥6.2 g/dL). Season of birth was the only variable associated with NCD (23% incidence), with calves born in the summer having higher odds of NCD (OR = 1.54; 95% CI: 1.08-2.20) than those born in the winter. For BRD (48% incidence), calves born in the fall had higher odds of BRD (OR = 1.51; 95% CI: 1.12-2.04) compared with winter-born calves, while calves born in the summer had lower odds (OR = 0.67; 95% CI: 0.51-0.88). Additionally, calves with excellent TPI had lower odds of BRD compared with those with poor TPI (OR = 0.71; 95% CI: 0.52-0.98). The odds of LC (51% incidence) were lower in calves with good (OR = 0.56; 95% CI: 0.38-0.82) or excellent (OR = 0.41; 95% CI: 0.28-0.61) TPI compared with poor TPI. Summer-born calves also had lower odds of LC than winter-born calves (OR = 0.72; 95% CI: 0.51-1.00). Lastly, each 1 kg increase in birth weight was associated with reduced odds of LC (OR = 0.96; 95% CI: 0.94-0.98). For mortality (3% incidence), calves born in the fall had lower odds (OR = 0.23; 95% CI: 0.05-0.97) of death compared with those born in the winter. Similarly, calves with good (OR = 0.13; 95% CI: 0.07-0.78) or excellent (OR = 0.34; 95% CI: 0.12-1.00) TPI status had reduced odds of mortality compared with those with poor TPI. In contrast, the odds of mortality were higher for calves with a health event compared with those with no health events (OR = 20.18; 95% CI: 4.24-96.13) and for calves with LC compared with those without LC (OR = 2.65; 95% CI: 1.02-6.88). These results identify some modifiable factors associated with preweaning calf health and survival and highlight the importance of improving colostrum management and early disease detection, as well as the influence of season.