To study the influence of electromagnetic fields in the short-wave range (3-30 MHz) radio transmitter signals on salivary melatonin concentration in dairy cattle.
Two dairy herds at two farms were compared, one located at a distance of 500 m (exposed), the other at a distance of 4,000 m (unexposed) from the transmitter.
Exposure duration: continuous for 2 days, then 3 days transmitter off, continuous for another 5 days
|Exposure duration||continuous for 2 days, then 3 days transmitter off, continuous for another 5 days|
|Distance between exposed object and exposure source||500 m|
|Sham exposure||A sham exposure was conducted.|
|magnetic field strength||1.59 mA/m||-||-||-||-|
The mean values of the two initial nights did not show a statistically significant difference between exposed and unexposed animals. A chronic melatonin reduction effect seemed unlikely.
However, on the first night of re-exposure after the transmitter had been off for three days, the difference in salivary melatonin concentration between the two herds was statistically significant, indicating a two- to seven-fold increase of melatonin concentration.
Thus, a delayed acute effect of electromagnetic field on melatonin concentration cannot completely be excluded. However, findings should be interpreted with caution and further trials are required.