Open Access

André L. A. Neves, Moritz A. Pfeiffer, Rajan Dhakal, Svenja Woudstra, Volker Krömker, Ricardo Augusto Mendonça Vieira

• We evaluated the effects of rapeseed oil (RSO, rich in oleic, linoleic, and linolenic acids) and a commercial fat source (BOVI-LM, rich in palmitic and stearic acids) on the growth performance and blood biochemical parameters of dairy calves during the pre- and post-weaning phases. Eighteen crossbred bull calves were randomly allocated in a randomized complete block design to three dietary treatments (Control, RSO, and BOVI-LM) during the milk-replacer phase (Phase 1, days 0–28). Due to technical issues, BOVI-LM supplementation was discontinued in Phase 2 (starter-feed phase, days 35–77), leaving only Control (n = 12) and RSO (n = 6). Energy supply was calculated to support target average daily gains of 0.6 (Phase 1) and 1.0 kg (Phase 2). Body weight, clinical health, and blood samples for biochemical analysis were monitored throughout the trial. No treatment effect on body weight or blood biochemical parameters was detected (main effect of treatment: p ≥ 0.18 for all analytes). In contrast, phase and time effects were significant for most biochemical parameters (p < 0.05), reflecting the metabolic transition from a milk-based to a solid-feed diet. Aspartate aminotransferase activity increased over time (p < 0.001), whereas glucose concentrations decreased post-weaning (time × phase: p = 0.020). The treatment × phase interaction was non-significant for all variables (p ≥ 0.13), supporting the absence of detectable carry-over effects and justifying the pooling of former BOVI-LM calves into the Control group in Phase 2.