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Effect of Electric and Magnetic Fields (60 Hz) on Production, and Levels of Growth Hormone and Insulin-Like Growth Factor 1, in Lactating, Pregnant Cows Subjected to Short Days

M. Rodriguez^*, D. Petitclerc, D.H. Nguyen, E. Block and J.F. Burchard^*

^* Department of Animal Science, McGill University, 21,111 Lakeshore Rd. Ste. Anne de Bellevue, QC, Canada H9X 3V9
Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Lennoxville, QC, Canada J1M 1Z3
Institut de Recherche d’Hydro-Québec (IREQ), Varennes, QC, Canada J3X 1S1
Church and Dwight Co. Inc.. 469 Harrison St. Princeton, NJ 08543-5297, USA

Electric and magnetic fields (EMF) are generated by the transmission of electricity through high tension lines traversing rural areas. Previous studies showed increased dry matter intake (DMI) and fat corrected milk in dairy cows exposed to EMF. Because EMF exposure has been shown to suppress pineal release of melatonin in some species, it was hypothesized that EMF effects resemble those of exposure to long days. Previous studies have shown that DMI and milk production increase in dairy cattle in response to long day photoperiods, and this has been observed in association with increased circulating insulin-like growth factor 1 (IGF-1), but not growth hormone (GH). The hypothesis that EMF act by modifying the response to photoperiod was tested by subjecting dairy cows to controlled EMF exposure while keeping them under short-day conditions. Sixteen lactating, pregnant Holstein cows were exposed to a vertical electric field of 10 kV/m and a horizontal magnetic field of 30 µT in a crossover design with treatment switchback. Two groups of eight cows each were exposed to EMF for 16 h/d in either of two sequences. Each sequence consisted of three consecutive 28-d periods. All animals were maintained under short day conditions (8 h light, 16 h dark) during the trial. DMI and plasma IGF-1 were increased (P < 0.01) during EMF exposure (17.03 vs.16.04 kg/d, SE = 0.4; 137 ± 6 ng/ml vs 126 ± 6, respectively). The mean GH concentration was not affected, but a treatment x hour interaction was detected, with GH lower for the EMF exposed animals during the first 16 h of the sampling period, and higher for the last 8 h. Overall, the yield of milk or its components was not affected by EMF exposure, but milk yield was significantly higher for the exposed animals during wk 4 of treatment.

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

Abbreviation key: EMF = electric and magnetic fields, MLT = melatonin, PRL = prolactin, GH = growth hormone

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