were allowed to farrow, subsequently bred again, and killed before term for examination of fetuses. The increase in the number of malformations in the fetuses was significant. Offspring from the second group allowed to farrow were killed after 10 months of exposure. No significant adverse effects were detected in those animals. These studies were complicated by a disease outbreak during the course of the second breeding of the first generation of sows. The presence of the disease and the associated exposure to electric fields make interpretation of the increase in the number of malformations detected in those animals very difficult.

Cattle

Algers and Hultgren (1987) exposed pregnant cattle to 50-Hz electric fields at 4 kV/m and magnetic fields at 2.0 µT (20 mG) by keeping the animals beneath 400-kV power lines. The animals were exposed continuously for 4 months. No changes were detected in fertility, estrous cycle, progesterone levels, intensity of estrous, viability of offspring, or incidence of malformations.

Nonmammalian Studies of Time-Varying Magnetic Fields

Chicken

Numerous studies have been done in which chicken eggs were exposed to magnetic fields. For a comprehensive review of these studies, the reader is referred to Chernoff et al. (1992). Because of the plethora of conflicting results reported in the literature and the lack of replication of studies by different laboratories, a multilaboratory definitive study was conducted; nearly identical protocols in six laboratories in six locations were involved (Berman et al. 1990).

Berman et al. (1990) exposed eggs to 100-Hz pulsed magnetic fields at 1-µT amplitude, 0.5-msec duration, and 2-msec rise and fall time. Exposure occurred for the first 48 hr of incubation. Embryos were then examined for fertility, developmental stage, and morphology. Two of six laboratories detected a decrease in the percentage of normal embryos as a function of the number of fertile eggs and live embryos. That effect was significant when the results of all laboratories were pooled. Interestingly, the results of this study reflect the range of previous studies in that the strongest effect was apparently the laboratory site. Unfortunately, because the strongest effect is more related to the laboratory site than to the fields used, the significance of the results of this study is difficult to determine, and the results do not give confidence that the study shows a true biologic effect of magnetic-field exposure.

As a follow-up to the study of Berman et al. (1990), Martin (1992) exposed eggs to 60-Hz peak-to-peak fields at 3 µT for the first 48 hr of incubation. In three subsets, the embryos were evaluated immediately after incubation; in one,



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