Growth during the first week of life and physiological body weight oscillation between feedings using high-frequency weighing in individually housed calves fed unrestricted amounts of milk twice daily

This study investigated early postnatal weight dynamics in 19 Brown Swiss calves (11 male, 8 female) during their first week of life. It was hypothesized that high-frequency weight monitoring during the first week of life in neonatal calves could reveal patterns of postprandial weight loss and early growth dynamics, which may be used to estimate metabolic activity. Calves were housed individually in hutches on calibrated scales that recorded BW every 10 s, enabling high-resolution monitoring of growth and postprandial weight changes. All calves were fed their dam's milk twice daily in unrestricted volumes for 14 feedings. Urine was quantitatively collected and weighed to estimate the proportion of weight loss attributable to metabolization and evapotranspiration. Data were analyzed using generalized linear mixed models with sex, feeding number, hours postprandial, and their interaction as fixed effects, and calf ID as a random intercept. A first-order autoregressive correlation structure accounted for autocorrelation in repeated measurements. Based on significant differences in weight-loss dynamics, feedings were grouped into early (1–3) and later (4–14) feedings. Sawtooth-like growth curves were observed for weight development during the first week of life due to daily fluctuations in BW with maxima occurring after feeding and minima before the next feeding. The calves showed an ADG of 1.31 ± 0.28 kg during the first week of life. Postprandial weight loss ranged from 3.5% to 7.4% of BW over 10 to 14 h and was significantly influenced by the feeding event and the duration of the postprandial period. The rate of weight loss was lowest during the first 3 feedings (0.346% BW/h), increasing and stabilizing at 0.607% BW/h at later feedings. Fourth-degree polynomial models best described the hourly postprandial weight loss patterns for feedings 1 to 3 and 4 to 14 (R 2 = 0.994 and 0.999, respectively). The highest weight loss occurred in the first hour postprandial and weight loss continuously decreased thereafter. Metabolization and evapotranspiration losses, calculated by the separation of the collected urine amounts from total weight loss observed on the scales, accounted for 79% of total weight loss at the first feeding and 33% to 49% in subsequent feedings. Strong positive correlations were found between postprandial weight loss to urine excretion (r = 0.729), and milk intake (r = 0.811). The findings highlight the dynamic nature of BW and the value of high-resolution, continuous monitoring (1 measurement every 10 s) in early calf development.