Biological effects of electric and magnetic fields on productivity of dairy cows.

Sixteen multiparous Holstein cows (weighing 600 +/- 50 kg, in 184.8 +/- 52 d of lactation, and at 101.9 +/- 43 d of gestation) were confined to wooden metabolic cages and exposed to a vertical electric field of 10 kV/ m and to a uniform horizontal magnetic field of 30 microT (microtesla). The trial was conducted as a switch-back statistical design. Cows were divided into two replicates of 8 cows each. One replicate was exposed for three periods of 28 d each. During the first period, the electric and magnetic fields were off; during the second period, they were on; and, during the final period, they were off. The second replicate was exposed for three periods also, but the activity of the fields was reversed (first period, on; second period, off; and third period, on). Blood samples were obtained twice weekly for the determination of cortisol and progesterone and once weekly for the determination of pH and blood gases. Milk samples were collected once weekly to determine milk components (fat, protein, SNF, and SCC). Milk yield and feed consumption were measured daily. Most of the variables studied (bicarbonate, pH, O2 and CO2 partial pressures, cortisol concentration in blood, uncorrected milk yield, and milk components other than milk fat) showed no variation that could be attributed to exposure to electric and magnetic fields. Associations were found between the electric and magnetic fields and increased DMI, 4% FCM yield, milk fat content, and plasma progesterone.