Benchmarking hydration, navel health, and transfer of passive immunity in surplus dairy calves.

Surplus dairy calves, or calves that are not used to replace the milking herd, are often sold within the first week of life and can sometimes receive suboptimal early-life care. The aim of this study was to assess the effect of delivering benchmarking reports to source dairy farms on the health of subsequent surplus calf cohorts. Briefly, 10 farms were first blocked by herd size category, and within each block, farms were alternately assigned to intervention and control in descending order of the previously measured proportion of calves with adequate passive transfer immunity (i.e., ≥5.8 g/dL total serum protein). After the initial randomization, 3 additional farms were enrolled by convenience to increase the statistical power, and one farm was assigned to the intervention group. Overall, 13 dairy farms were recruited and assigned to intervention (n = 6) and control (n = 7) groups. The intervention group received health benchmarking reports of surplus calves delivered to calf dealers halfway through the study period, whereas the control group received no reports. Between May 2021 and June 2022, a total of 282 and 371 calves enrolled from intervention and control farms, respectively, were assessed for hydration, navel health, and transfer of passive immunity (TPI). In brief, hydration was evaluated using the skin tent test and a 4-point scale, and navel health was assessed based on the width of umbilical cords using a 4-point scale. The TPI was assessed based on the concentration of total serum protein. In November 2021, benchmarking reports containing health metrics of calves from 13 farms during the first 6 mo of the study were delivered to 6 intervention farms. Differences in health metrics of subsequent surplus calf cohorts between intervention and control farms were investigated using generalized linear mixed models specified to recognize "farm" as the experimental unit. Prevalence of dehydration was decreased in calves from intervention farms compared with control farms after receiving the benchmarking reports (odds ratio = 0.19, 95% CI = [0.04, 0.90] %). There was no evidence of any differences in navel inflammation or failure in TPI associated with benchmarking reports. Results suggest delivering benchmarking reports to dairy producers may improve hydration in surplus calves. Nevertheless, additional methods should be investigated to improve calf health within the surplus calf production chain.