A randomized controlled trial evaluating the effect of providing a rest period during long-distance transportation of surplus dairy calves: Part I. Impact on health, growth, and activity.

The objective of this randomized controlled trial was to determine if providing a rest period (RP) to surplus calves transported for 16 h reduced the impact of long-distance transportation on health, growth, and activity after arrival to a calf-raising facility. Between September 2022 to January 2023, 6 to 24 d old surplus calves were randomly assigned to one of 2 treatment groups: 1) continuous transportation by road for 16 h (n = 86) or 2) 8 h of transport, 8 h RP, then a further 8 h of transport to a single commercial calf-raising facility in Ontario, Canada (n = 84). Calves that received the RP were fed 2 L of milk replacer at the time of unloading for the RP and again before reloading for the second leg of transportation. Calves were weighed before and after transportation and once weekly until they left the calf-raising facility at 11 weeks after arrival. Additionally, fecal consistency and respiratory health were assessed immediately before and after transportation, as well as twice daily following arrival. The odds of abnormal fecal and respiratory scores were assessed with mixed effects logistic regression models, whereas cox proportional hazards models were used to evaluate the hazard of treatment for diarrhea and respiratory disease. To evaluate weight loss during transportation, average daily gain, lying bouts, and steps, mixed linear regression models were used. Furthermore, mixed logistic regression models with repeated measures were built to assess associations with the odds of having a sunken flank and prolonged skin tent. There were no statistical differences in the odds of abnormal fecal or respiratory scores or the treatment for diarrhea between treatment groups; however, there was evidence that calves that received a rest period had a higher hazard of treatment for respiratory disease. Calves >10 d old had reduced odds of having an abnormal respiratory score and calves 13–24 d old had lower odds of arriving with a prolonged skin tent, lower odds of abnormal fecal score, and reduced hazard of treatment for diarrhea compared with calves 6–8 d old at transportation. During transportation, calves that received a rest period lost less weight than continuously transported calves. With respect to ADG over the 77-d study, an interaction between age at transport and treatment group was identified where calves aged 9 to 10 d old and received a rest period had higher ADG compared with calves that were 9 to 10 d old and did not receive a rest period. As for calf activity, calves receiving an RP spent more time lying on the day after transportation compared with calves that were continuously transported. The results of this trial show few differences in the health and growth of calves having a RP compared with those that underwent continuous transport. Furthermore, calves receiving a rest period may arrive more fatigued than calves who arrive to their destination in a shorter period of time overall. Transporting calves at older ages presents an opportunity to reduce the impact of long-distance transportation on subsequent health, growth, and activity.