Impact of transport source (dairy farms vs. collection center) and post-arrival housing in combination with prophylactic antibiotic treatment on performance, lung health and microbiota of veal calves

Transport via a collection center and early life administration of antibiotics are two major challenges faced by calves in current veal husbandry management. The main aim of this proof of concept study was to investigate the effects of these two factors on fecal microbiota, lung immunity, and overall health of veal calves. The study had a 2 × 2 factorial design with the following factors: source of calves [transport via a collection center (CC) or direct transport from dairy farms (DF)], and early-life administration of antibiotics (AB or no AB). The hypothesis was that direct transport and AB use may positively affect the health of calves. A total of 89 bull calves and 5 heifers, aged two to 4 weeks, and with average 46.4 ± 5.1 kg body weight (BW) at arrival were included in the study. The study was performed in two consecutive batches, and calves were followed for a period of 8 weeks. At arrival, animals were housed in groups of three calves/pen divided over six rooms. Calves from the DF were housed in separate rooms, whereas CC calves were housed in multiple pens per room. The AB-treatments received an oral antibiotics/antiphlogistic treatment via the milk replacer on day 4 after arrival. On day 21 and 45, fecal samples and broncho-alveolar lavage fluid (BALF) were collected, whereas nasal swabs were collected on day 7 for microbiota analysis. Blood samples were collected on day 1, 7, 21, 35, 45, and 51 for the complete hematological profile and immune cells. Body weights were recorded upon arrival, and day 28 and 49, and clinical observations were conducted twice a week throughout the experiment. Post-mortem examinations were also performed. Calves sourced from CC and not receiving AB (CC_No AB) had the lowest percentage of alveolar macrophages, the highest incidence of clinical problems and the lowest BW at the end of the trial. Fecal Shannon index and Pielou's evenness was reduced in CC_AB calves compared to all other treatments. Calves sourced via CC showed a higher lung/heart ratio and more abnormalities in the lungs compared to DF calves. Overall, this study showed that transportation via a CC without subsequent treatment with AB represented the greatest challenge on clinical health, immunity, and fecal microbiota of veal calves.