PROGESTERONE CONCENTRATIONS DURING ESTROUS-CYCLE OF DAIRY-COWS EXPOSED TO ELECTRIC AND MAGNETIC-FIELDS

Sixteen multiparous nonpregnant lactating Holstein cows (each weighing 662 +/- 65 kg in 150.4 +/- 40 day of lactation) were confined to wood en metabolic cages with 12:12 h light:dark cycle during the experiment . The cows were divided into two sequences of eight cows each and expo sed to electric and magnetic fields (EMF) in an exposure chamber. This chamber produced a vertical electric field of 10 kV/m and a uniform h orizontal magnetic field of 30 mu T at 60 Hz. One sequence was exposed for three estrous cycles of 24 to 27 days. During the first estrous c ycle, the electric and magnetic fields were off; during the second est rous cycle, they were on; and during the third estrous cycle, they wer e off. The second sequence was also exposed for three 24 to 26 days es trous cycles, but the exposure to the fields was reversed (first estro us cycle, on; second estrous cycle, off; third estrous cycle, on). The length of each exposure period (21 to 27 days) varied according to th e estrous cycle length. No differences were detected in plasma progest erone concentrations and area under the progesterone curve during estr ous cycles between EMF nonexposed and exposed periods (2.28 +/- 0.17 a nd 2.25 +/- 0.17; and 24.5 +/- 1.9 vs. 26.4 +/- 1.9 ng/ml, respectivel y). However, estrous cycle length, determined by the presence of a fun ctional corpus luteum detected by concentrations of progesterone equal to or more than 1 ng/ml plasma, was shorter in nonexposed cows than w hen they were exposed to EMF (22.0 +/- 0.9 vs. 25.3 +/- 1.4 days). Bio electromagnetics 19:438-443, 1998. (C) 1998 Wiley-Liss, Inc.