Effects of age and feeding protocols on the metabolic and physiological condition of unweaned calves during and after long-distance transport.

backgroundLong-distance transport and associated extended fasting periods challenge the physiological state of young calves, leading to energy loss, dehydration, and potentially hunger and exhaustion. Older calves with greater body reserves may better withstand fasting, while providing larger volumes of milk replacer pre-transport could help sustain energy balance and hydration. The aim of this study was to investigate how calf age and pre-transport feeding protocols affect the physiological status of unweaned calves during and after long-distance road and ferry transport.

resultsWe followed a commercial shipment of 138 male dairy calves from an assembly centre (AC) in Ireland via road and roll-on-roll-off ferry to a lairage in France and then via road to a veal farm in the Netherlands (total transport duration 51 h). Study design was a 2 × 2 factorial with factors calf age (2–3 or 4–5 weeks) and pre-transport feeding protocol (2–4 L of milk replacer). We collected four blood samples (AC, lairage, arrival, Day 7 post-transport) and analysed them for 15 variables indicating energy balance, hydration status, muscle fatigue, and physiological stress responses. Twenty calves were fitted with continuous glucose monitors (CGMs) to measure interstitial glucose from 13 h before to 90 h after departure. Body weight was recorded at AC, lairage, arrival, Day 7 and 21 post-transport. The effects of age and feeding protocol on physiological responses were assessed using linear mixed models with repeated measures and random effects for calf and farm of origin. Younger calves weighed less than older calves overall (49.8 vs. 53.0 kg, P = 0.004) and at all sampling moments; they had higher plasma glucose concentrations than older calves overall (4.61 vs. 4.42 mmol/L, P = 0.038) and at all sampling moments except lairage, lower sodium concentrations at arrival (139.9 vs. 140.8 mmol/L, P = 0.034) and lower chloride concentrations at AC (97.4 vs. 99.0 mmol/L, P < 0.001) and lairage (96.6 vs. 97.5 mmol/L, P = 0.009). Calves fed 2 L pre-transport had lower CGM glucose readings for two hours after feeding at AC and higher urea concentrations at lairage (4.01 vs. 3.10 mmol/L, P < 0.001) than calves fed 4 L.

conclusionAlthough feeding 4 L compared to 2 L before transport had some positive effects on calf energy balance and hydration, our findings suggest that pre-transport feeding has only limited capacity to alleviate the negative impacts of transport and prolonged fasting on the physiological status of calves, especially during multi-day transport. Effects of age on calf resilience were few and inconclusive, and further research should include a larger age range.