Evaluation of the endocrine response of cattle during the relocation process

To evaluate the endocrine responses associated with the relocation process, 22 Holstein heifers (326.4±46.8 kg BW) were randomly assigned to control (CON) or relocation (RELOC) treatment groups. On d 0, heifers were weighed and fitted with indwelling rectal temperature (RT) monitoring devices and jugular catheters. On d 1, baseline blood samples were collected from all heifers for 2 h prior to the transportation event, then weighed. Controls were returned to tie stalls and RELOC were loaded into a modified stock trailer (12 individual stanchions) for a 4 h transportation event. Simultaneous blood samples were obtained at 30-min intervals from both groups throughout the 4 h transport event (TE-I). After transport, RELOC were unloaded at an unfamiliar location, weighed, and placed in tie stalls for a 2 h post-transportation period. All heifers were then placed into two separate holding paddocks with access to water and hay for 4 h. After 4 h, hay and water was withdrawn for 20 h. On d 2 RELOC heifers were exposed to a second transport event (TE-II); the timeline and procedures of TE-II were identical to those of TE-I (except for the starting point for RELOC heifers). All serum samples were analyzed for concentrations of cortisol, growth hormone (GH), and insulin-like growth factor-I (IGF-I). A 6% reduction in BW for the RELOC as compared to 2.5% reduction in BW for CON (P<0.001) was observed during TE-I. Overall BW loss was 2% greater (P<0.02) for RELOC heifers compared to CON heifers. During TE-I, RELOC heifers had greater RT (P<0.05) compared to CON heifers. There was treatment×time interaction observed for cortisol (P<0.003); RELOC had greater cortisol concentrations at multiple time points throughout TE-I and -II. No differences (P>0.05) in area under the curve (AUC) for cortisol were observed during TE-I. However, AUC for total cortisol during TE-II was greater (P<0.01) in the RELOC group compared to CON. There were no differences in AUC for GH between treatment groups for TE-I or -II, but a transient decline (P<0.05) within each group was observed from d 1 to d 2. There were no differences (P>0.05) in IGF-I concentrations or in AUC between the treatment groups during TE-I and -II or from d 1 to d 2. Results provide evidence that the actual processes surrounding the transportation of cattle, can elicit a stress response, as defined by increased concentrations of cortisol, RT, and BW losses.