Plasma cortisol was greatly elevated with the onset of transportation in the current study when compared with −24 h (Figure 4A), a 321% increase at 4.5 h (42.54 ± 2.10 ng/mL compared with 13.22 ± 1.30 ng/mL at −24 h). Cortisol concentrations reached nadir at 14.25 h at 6.99 ± 1.34 ng/mL before returning to basal concentrations at 24 and 48 h post transportation. The steroid hormone DHEA was decreased by 30% at 4.5 h (1.17 ± 0.124 ng/mL vs. 1.52 ± 0.15 ng/mL at −24 h; Figure 4B), when cortisol reached its peak. The cortisol: DHEA ratio followed the curve of plasma cortisol very closely, elevated by 528% at 4.5 h (74.62 ± 16.06 compared with 14.12 ± 2.39 at −24 h; Figure 4C).
Plasma concentrations of the steroids testosterone and progesterone were also measured. Plasma testosterone was depressed with transportation stress, reaching its lowest point at 4.5 h (4.05 ± 0.20 ng/mL), 74% less than −24 h (15.41 ± 1.88 ng/mL; Figure 4D). In contrast, plasma progesterone, although present at low concentrations in bulls, was elevated at 4.5 h (0.43 ± 0.047 ng/mL), increased by 215% its −24-h concentration (0.19 ± 0.02 ng/mL; Figure 4E). Profiles of all steroidal changes are shown in Figure 4, and P-values are shown in Table 1.