In experiment 1, 16 lactating pregnant cows were divided in two groups and exposed to electromagnetic fields. Each group was exposed according to one of two treatment sequences of three periods of 28 days each: Sequence 1 was "electromagnetic field OFF-ON-OFF" and sequence 2 was "electromagnetic field ON-OFF-ON". During the last day of each period, blood samples were collected every 4 h for 24 h to determine thyroxine plasma concentrations.
In experiment 2, 16 non-lactating, non-pregnant, multiparous cows were divided in two groups and each group was also exposed according to one of the two treatment sequences described above, except that each period amounted to the number of days corresponding to one estrous cycle (estrous cycles were synchronized). During treatment, blood samples were collected every other day.
The light cycle was 8 h light/16 h dark (short-day condition). During the ON periods, the cows were irradiated for 16 h: 8 h of the light period plus the first 8 h of during the dark period.
|Chamber||15 m long x 10 m wide x 3 m high chamber containing 8 wooden box stalls, each holding one cow.|
|Setup||Exposure was performed with rectangular coils 10 m long x 4 m high for MF and two plates 9 m long x 6.5 m wide suspended 6.5 from ceiling for EF.|
|Additional info||16 lactating, pregnant and 16 non-lactating, non-pregnant Holstein cows were divided into two replicate groups of eight cows each. Each replicate was exposed to EMF in one of the two sequence of three periods. The first replicate had 28 non-exposed followed by 28 days exposed and then 28 days non-exposed (Off/On/Off) where as the second replicate was 28 days exposed, 28 days non-exposed and 28 days exposed (On/Off/On).|
The data indicated that a worst case scenario exposure of dairy cattle to 10 kV/m, 30 µT electromagnetic field influenced, in a moderate fashion, the blood levels of thyroxine.
In experiment 1, exposed cows did not have any change in thyroxine plasma concentrations due to treatment, but the effect of "sampling hour" was significant (both control and treated cows had higher thyroxine concentrations at 04:00 A.M. which declined when the light was turned on at 08:00 A.M.).
In experiment 2, the effect of "period" and the "treatment by days interaction" (two different calculated measurement parameters) were statistically significant. The data indicated that exposure to electromagnetic fields produced a 3.8% increase in thyroxine plasma concentration.