Effects of Electric and Magnetic Fields on Nocturnal Melatonin Concentrations in Dairy Cows

¹ Department of Animal Science, McGill University, 21,111 Lakeshore, Sainte Anne de Bellevue, QC, Canada H9X 3V9
² Institut de Recherche d'Hydro-Québec, Varennes, QC, Canada J3X 1S1

Sixteen multiparous, pregnant, lactating Holstein cows (weighing 600 ± 50 kg, at 184.8 ± 52 d of lactation, and at 101.9 ± 43 d of gestation) were confined to wooden metabolism cages and exposed to a vertical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 µT. The trial was conducted using a switchback statistical design. Cows were divided into two sequence groups of 8 cows each. One sequence group was exposed for three periods of 28 d each. The electric and magnetic fields were off during the first period, on during the second period, and off during the final period. The second sequence group was exposed for three periods also, but the activity of the fields was reversed (on during the first period, off during the second period, and on during the third period). On d 25 of each exposure period, blood 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 electric and magnetic fields.

Key Words: melatonin • electric field • magnetic field • cows

Submitted on April 22, 1996
Accepted on August 22, 1997