EFFECTS OF ELECTRIC AND MAGNETIC-FIELDS ON NOCTURNAL MELATONIN CONCENTRATIONS IN DAIRY-COWS

Sixteen multiparous, pregnant, lactating Holstein cows (weighing 600 /- 50 kg, at 184.8 +/- 52 d of lactation, and at 101.9 +/- 43 d of ges tation) were confined to wooden metabolism cages and exposed to a vert ical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 mu T. The trial was conducted using a switchback statistical. d esign. Cows were divided into two sequence groups of 8 cows each. One sequence group was exposed for three periods of 28 d each. The electri c and magnetic fields were off during the first period, on during the second period, and off during the final period. The second sequence gr oup was exposed for three periods also, but the activity of the fields was reversed (on during the first period, off during the second perio d, and on during the third period). On d 25 of each exposure period, b lood samples were obtained every 0.5 h for 14 h starting at 1700 h to determine melatonin concentration. Nocturnal melatonin concentrations did not show any variation that could be attributed to exposure to ele ctric and magnetic fields.