Transportation decreases the pulse frequency of growth hormone in the blood of prepubertal male calves.

Both the mean concentration and the pulse pattern of growth hormone (GH) in the blood are important for the metabolism and body growth of calves. Transportation is reported to decrease blood GH concentrations in prepubertal male calves. However, the effect of transportation on GH pulsatility remains unknown. Because transportation is important in moving these calves from calf-production farms to markets or fattening farms, we tested whether transportation decreases their GH pulse frequency. Five calves were subjected to transportation by trucking (transport group), while five were left in their shed (non-transport group). Both groups were subsequently subjected to frequent blood sampling at 15-min intervals for 5 h. In the transport group, the cortisol concentrations increased in the first hour (P < 0.05) but significantly decreased thereafter (P < 0.05) to lower than those of the non-transport group. During the 5-hour study period, the transport group displayed a similar mean GH concentration relative to the non-transport group, but displayed a delayed first GH pulse, and a lower number of GH pulses than the non-transport group (P < 0.05). Hence, transportation is suggested to decrease GH pulse frequency under abnormal cortisol states, presumably suppressing metabolism and body growth in prepubertal male calves.