Veal calves management in Québec, Canada: Part II. Association between passive immunity transfer at arrival and...

The average daily gain (ADG) of veal calves is an important outcome to monitor for veal producers to maximize profitability. Transfer of passive immunity (TPI) is of paramount importance in dairy and beef calves. There is little information available that examine the relationship between TPI and ADG of veal calves in Québec. The objective of this study was to investigate the effect of arrival risk factors associated with lower ADG in milk and grain-fed veal calves in Québec. Between October 2017 and December 2018, a prospective cohort study was conducted on 59 batches of milk- and grain-fed veal calves in different geographic locations in Québec, Canada (n = 1729 calves). After arrival, thirty calves per batch were randomly sampled for estimating TPI using the Brix refractometer (serum threshold < 8.4 % for inadequate TPI). Throughout the production cycle, all health records of each batch of calves were extracted and used to quantify individual- and group-level risk factors. After the elaboration of a causal diagram using directed acyclic graphs, ADG was modelled through linear mixed models (LMMs) as function of categorical variables (individual inadequate TPI, arrival season, purchasing sites, and weights at purchase) and a continuous contextual variable (proportion of inadequate TPI in the batch). Also, the impact of morbidity (treated vs non treated) on ADG was investigated through linear regression model. Because performance and health data are typically underreported in commercial settings, data missingness was identified as a potential concern. Therefore, multiple imputation models were used. A total of 1084 calves had Brix % < 8.4 % giving a prevalence of 62.7 % of inadequate TPI. Individual calves with inadequate TPI gained 0.02 kg/d less than those with adequate TPI. Batch-level inadequate TPI prevalence was not associated with ADG difference in the sampled calves. Calves arriving to the facility during summer gained 80 g/d less than those arriving during fall. Calves treated at least once with antibiotic had lowered ADG by 7.2 kg throughout the production cycle compared to untreated calves. In conclusion, this study suggests that individual-level inadequate TPI assessed upon arrival in the facility, arrival season, and antibiotic treatments during the production cycle are associated with lowered ADG in veal calves.