Evaluation of continuous interstitial glucose monitoring in healthy calves

In newborn calves, glucose is the primary energy source, gradually replaced by volatile fatty acids produced by the developing rumen microbiota. Although blood glucose monitoring is essential, there is currently no consensus on optimal measurement methods in calves. Current techniques rely on frequent blood sampling, which is invasive, stressful, and could itself influence glucose levels. Continuous monitoring of interstitial glucose using sensors offers a non-invasive alternative that enables tracking of glycemic fluctuations over several days. This study evaluated the feasibility of using such sensors in 6 male dairy calves aged 15 to 38 d. Five sensors were placed at different anatomical sites: the base of the ear, neck, thorax, rump, and inner thigh. Jugular blood glucose levels, measured 8 times a day using the hexokinase method, were compared with sensor data using Passing-Bablok regression for repeated measures. Sensors placed on the rump and thorax demonstrated the longest functional lifetimes, along with a constant negative bias (intercept) and a positive proportional bias (slope) compared with the reference standard. Accordingly, the sensors underestimate glucose at low concentrations, while tending to overestimate it as blood glucose levels increase. Despite suboptimal analytical accuracy, these sensors showed sufficient accuracy to support the investigation of milk-feeding practices and metabolic transition in calves.