Authored by: Maren Fedrowitz
Published on: Sep 05, 2014
Department of Pharmacology, Toxicology, and Pharmacy
University of Veterinary Medicine
Effects of electromagnetic fields (EMF) on cows have been frequently discussed in public media as well as in specialist journals and meetings with agricultural, veterinary or dairy backgrounds. Indeed, in view of the available literature, it does seem that cows show EMF susceptibilities and respond to environmental exposures of a broad range of frequencies and properties:
- Cows are sensitive to the Earth´s magnetic field. Bovine magnetoreception can be influenced by external EMF, e.g. powerlines.
- Several physiological alterations in dairy cows exposed to extremely low frequency (ELF) EMF were reported without major indications for adverse health effects. Notably, the observed effects seem to be dependent on the magnetic field component or on combined electric and magnetic fields rather than on electric field exposure alone.
- Cows are sensitive to earth currents (stray voltage) associated with transients in particular harmonics. Milk production, health, and behavior seem to be negatively affected.
- Bovine responses to radiofrequency (RF) exposure include avoidance behavior, reduced ruminating time, and alterations in oxidative stress. These findings indicate possible adverse health effects. However, most of the studies have critical points (one-herd-case report, logistic problems in study design, lack of appropriate exposure assessment) that confirmation of the observed RF effects is clearly needed, though studies in such big animals are time-, place-, and money-consuming, and exposure assessment and dosimetry are challenging issues.
Overall, cattle seem to be affected by environmental EMF exposure. Cows are nowadays subject to closely calculated economic constraints and have to calve as often as feasible to ensure production of milk and beef. During this process, the animal´s physiological balance is frequently at its limit. This explains why cows may be extremely sensitive to additional stress factors, e.g. EMF. Bovine EMF sensitivity raises on the one hand interesting questions about mechanisms to explain how cows sense the Earth´s magnetic field and are influenced by man-made EMF, including possible health hazards, which might be translated to humans and help to improve human risk assessment. On the other hand, concerns would be raised about the economic consequences if milk production, fertility, and growth performance were affected. At the current level of knowledge, it has not been clarified whether the consequences of EMF exposure are “influences on physiology” without pathophysiological effects, whether EMF exposure is associated with any deficits in bovine performance and economic disadvantages, or whether EMF exposure seriously affects the animals´ health.
Cows align to geomagnetic field lines and are influenced by ELF EMF
There is a discussion about the ability of cattle to sense the Earth´s magnetic field, about mammalian magnetoreception and the underlying mechanisms. This has been initiated by Begall et al. (PNAS, 2008), who used satellite images provided by Google Earth to evaluate the direction of grazing and resting ruminants, e.g. cows and deer, and included a huge number of animals and herds around the globe in their study. The authors found that cattle align their body in a north-south direction, propose that the animals orient along the field lines of the Earth´s magnetic field, and thereby describe for the first time the existence of a magnetic sense in cattle. In a consecutive paper, the group describe how ELF EMF might disrupt the magnetic alignment of ruminants (Burda et al. PNAS, 2009).
In contrast, an investigation by Hert et al. (J Comp Physiol A, 2011) did not confirm alignment of cattle along geomagnetic field lines. However, Begall et al. (J Comp Physiol A, 2011) replied that Hert et al. used images of low quality as well as a different statistical approach for their evaluation and did not consider influence from external EMF, e.g. high-voltage powerlines. These findings and discussions about possible magnetoreception in cattle stirred much attention, were picked by the media and discussed in Nature by Daniel Cressey (Nature News, 2008 & 2011, Nature News Blog, 2009).
The team around Burda and Begall continues to look at magnetoreception in other animals, already adding foxes, dogs, and other species to their list (Cerveny et al. Biol Lett, 2011; Hart et al. Frontiers Zoology, 2013), and showed some of their results at this year´s BioEM meeting in South Africa. In 2013, Slaby et al. (J Comp Physiol A, 2013) confirmed alignment along a North-South axis in cattle and suggested that the alignment depends on herd density because it disappeared in herds with higher cow densities.
The mechanism underlying how cattle might sense the Earth´s magnetic field and how it can be disturbed by external influences, e.g. powerlines, remains currently unknown. Recently, Eder et al. (PNAS, 2013) identified magnetic cells, which contain intracellular structures of iron-rich crystals coupled to the cell membrane, and determined their dipole moments. The authors conclude that these cells are able to work as magnetoreceptors and to detect even small changes in the external magnetic field. Although performed in fish epithelial cells, these investigations could probably also provide explanations for the interaction mechanisms of EMF and magnetoreception in cattle.
Cows and ELF electric and magnetic fields
In the 1980s, field studies investigating estrous cycle, fertility, and growth performance in cattle near transmission lines revealed no effects for any of the examined parameters (Algers & Hennichs. Prev Vet Med, 1985; Algers & Hultgren. Prev Vet Med, 1987; Angell et al. Bioelectromagnetics, 1990). Broucek et al. published two studies about effects of ELF exposure for several weeks and did not observe any effects associated with adverse health effects concerning growth behavior in calves or bovine reproduction. However, they reported a decreased milk yield and shorter calving intervals (Broucek et al. Tierärztl. Umschau, 2001 & 2002). In hematological and immunological investigations, Stelletta et al. (Biomed Environ Sci, 2007) found higher counts of T lymphocytes after exposure of cows to field strengths of about 2.0-3.3 µT from 380 kV transmission lines, but group sizes were quite small (n=5).
From 1996 to 2007, Burchard, Nguyen, and colleagues published experimental studies on effects of ELF electric and magnetic fields in dairy cows in 13 papers (probably more). A series of eight publications appeared in Bioelectromagnetics. In 2005, the authors described the development of an exposure chamber for cows (Nguyen et al. Bioelectromagnetics, 2005). In most of their studies, the animals were exposed to 60 Hz, 10 kV/m, 30 µT for several 28-day-periods (except in some studies with a shorter exposure, e.g. 16-day-periods). Body weight, feed intake, milk production and composition as well as many other parameters were examined, mostly in plasma samples, sometimes in cerebrospinal fluid of pregnant or non-pregnant cows or heifers.
Alterations in milk production and milk fat, which were correlated with week of exposure, were noticed, and the data suggested an adaption response of the animals (Burchard et al. J Dairy Sci, 1996; Rodriguez et al. J Dairy Sci, 2002; Burchard et al. Bioelectromagnetics, 2003). Almost no ELF EMF effects on progesterone were observed (Burchard et al. Bioelectromagnetics, 1998 & 2004; Burchard et al. J Dairy Sci, 1996; Rodriguez et al. Anim Reprod Sci, 2003). However, several studies revealed a prolonged estrous cycle in exposed animals (Burchard et al. Bioelectromagnetics, 1998; Rodriguez et al. Anim Reprod Sci, 2003).
Melatonin showed a tendency for a decrease in light period, but no effects during night (Burchard et al. J Dairy Sci, 1998). Prolactin and thyroxine were altered in some experiments (Rodriguez et al. Bioelectromagnetics, 2004; Burchard et al. Bioelectromagnetics, 2006 & 2007). Trace minerals in cerebrospinal fluid were affected in a more pronounced way than in plasma or compared to macroelement concentrations (Burchard et al. Bioelectromagnetics, 1999). Quinolinic acid was increased in exposed animals indicating weakening in blood brain barrier (Burchard et al. Neurochem Res, 1998).
Interestingly, there were no effects at all when only electric fields were applied. Thus, magnetic fields, alone or in combination with electric fields, are needed for ELF effects in bovines (Burchard et al. Bioelectromagnetics, 2004). After MF exposure, slight effects on body weight, prolactin, and insulin-growth-factor-1 were observed but without any indications for major animal health hazard (Burchard et al. Bioelectromagnetics, 2007).
Overall, several - though not all - studies in cows revealed alterations in physiological parameters after exposure to ELF MF or EMF, but it is currently not possible to link the observed effects to bovine health hazard or economic consequences.
Cows and stray voltage fields
With respect to influences of stray voltage, a meta-analysis by Erdreich et al. (J Dairy Sci, 2009) concludes that bovine behavioral responses to currents are threshold-dependent and unlikely to appear below 3 mA. Evaluations addressing milk production were difficult because studies were too different to be merged together. The authors summarize that they did not observe any indications that production was affected by exposure to up to 3 mA for up to 3 or 4 weeks.
A recent field study by Hillman et al. (Sci Total Environ, 2013) confirmed that dairy cows were sensitive to earth currents. In contrast to Erdreich et al. (J Dairy Sci, 2009), the findings of Hillman et al. (Sci Total Environ, 2013) indicate that not only the cows´ behavior, but also health and milk production were negatively affected by harmonic distortions.
Cows and RF exposure
Descriptions of bovine responses to RF exposure, e.g. on pastures near mobile phone base stations or radio broadcast transmitters, are often anecdotal stories from concerned animal owners. There are only a few sources which try to clarify possible RF effects in cattle in a scientific way. One reason for this might be that exposure assessment or dosimetry in such big animals is very sophisticated and difficult to achieve in view of available time and funding.
Stärk et al. (J Pineal Res, 1997) performed a field study with five cows per group and did not notice any chronic alterations in salivary melatonin in cows exposed to a short-wave broadcast signal. At the same time, a case report about reduced milk yield, health problems (e.g. avoidance behavior, poor general condition, conjunctivitis), and behavioral abnormalities in dairy cows exposed to TV and radio transmitting antennas attracted much attention (Löscher & Käs. Prakt Tierarzt, 1998). The abnormalities occurred when another transmitter was installed in addition to several already existing RF sources. The RF fields, as well as the animals´ housing, feeding conditions and health status, were well characterized. Many other reasons, e.g. infections, for the observed abnormalities could be excluded. Thus, the observed problems might indeed have been induced by RF.
Triggered by this case report, a field study including 38 herds, which were divided into 4 exposure groups and observed for 2 years, was performed. Investigations on the animals´ performance and behavior, milk production, fertility, bovine diseases as well as immunological, serological, parasitological, and genotoxic statuses were conducted (Bavarian Study, 2001). Unfortunately, serious logistical problems in the study design, mainly an inhomogeneous distribution of housing conditions and health status, prevent any clarification as to whether the apparent differences, e.g. an increase in birth defects, were associated with RF exposure or rather with the existence of the well-known disease bovine viral diarrhea (BVD). Findings concerning behavioral data were published and show significant differences in lying behavior, daily behavior on pasture and ruminating behavior in response to RF EMF exposure (Wenzel et al. Prakt Tierarzt, 2002). As ruminants are very sensitive to disturbances of their daily routine and digestion, the observed alterations can be considered as an expression of chronic stress and an indication for a biological effect of RF EMF (Wenzel et al. Prakt Tierarzt, 2002), which might lead to a reduction in performance or might influence the animal´s health (Löscher. Prakt Tierarzt, 2003). Altogether, the data from the Bavarian study (2001) are unfortunately only useful as a negative example for inappropriate study design. The study aimed to investigate effects of RF EMF but possible influences by BVD did not allow any clear statement. Therefore, the probability of health hazards in cattle caused by RF EMF can neither be confirmed nor excluded (Bavarian study, 2001).
Recent studies in Switzerland deal with determinations of oxidative stress in bovine samples due to exposure from mobile phone base stations. Hässig et al. (Schweiz Arch Tierheilkd, 2009) investigated the prevalence of cataracts in veal calves and found an association between the location of calves with cataracts in the first trimester of gestation and RF exposure from mobile communication antennas. Moreover, there was a correlation of increased oxidative stress in the eyes with cataracts and the distance to the nearest base station. However, one big disadvantage of the study is that exposure assessment was done in an unsatisfactory and uncertain way and might differ from real exposure of the individual cow, fetus, or calf on the farm.
In a second study, Hässig et al. (BMC Vet Res, 2014) examined activities of enzymes associated with oxidative stress in the blood of adult female cows (n=10) exposed to applied RF. Ambient conditions as well as the exposure set-up were well characterized and the experimental design included pre-exposure, exposure, and post-exposure periods. RF exposure was able to induce changes in enzyme activities. Interestingly, individual response patterns were observed, indicating the existence of sensitive and non-sensitive cows. For future studies, the authors recommend to investigate parameters at later time points or for a longer post-exposure period.
In summary, RF exposure seems to induce biological responses in cattle. The reported findings (avoidance behavior, reduced ruminating and lying times, alterations in oxidative stress enzymes) suggest the possibility of adverse health effects in cows exposed to RF. However, the observed effects need confirmation as data were from a one-herd-case report, suffer from logistic problems, or lack appropriate exposure assessment. Hopefully, the kind of investigations proposed by the last study of Hässig et al. (BMC Vet Res, 2014) will be continued.
Overall, cows seem to respond to environmental EMF exposure at a broad range of frequencies. This susceptibility might be due to the fact that nowadays bovines are at their physiological limits regarding milk and beef production. Addition of another – even weak - stressor is enough to alter the fragile physiological balance. Therefore, cattle could be considered as an appropriate model to study EMF effects as well as mechanisms, if they weren´t so big and cow dosimetry were not so complex.
Magneto-reception in cows and other mammals:
Begall S, Cerveny J, Neef J, Vojtech O, Burda H. Magnetic alignment in grazing and resting cattle and deer. PNAS, 2008, 105:13451-13455
Burda H, Begall S, Cerveny J, Neef J, Nemec P. Extremely low-frequency electromagnetic fields disrupt magnetic alignment of ruminants. PNAS, 2009, 106:5708-5713
Hert J, Jelinek L, Pekarek L, Pavlicek A. No alignment of cattle along geomagnetic field lines found. J Comp Physiol A, 2011, 197:677-682
Begall S, Burda H, Cerveny J, Gerter O, Neef-Weisse J, Nemec P. Further support for the alignment of cattle along field lines: reply to Hert et al. J Comp Physiol A, 2011, 197:1127-1133
Cressey D. Magnetic cows are visible from space. Nature News, 2008 http://www.nature.com/news/2008/080825/full/news.2008.1059.html
Cressey D. Return of the B-field bovines. Nature News Blog, 2009 http://blogs.nature.com/news/2009/03/return_of_the_bfield_bovines.html
Cressey D. The mystery of the magnetic cows. Nature News, 2011 http://www.nature.com/news/the-mystery-of-the-magnetic-cows-1.9350
Slaby P, Tomanova K, Vacha M. Cattle on pastures do align along the North-South axis, but the alignment depends on herd density. J Comp Physiol A, 2013, 199:695-701
Cerveny J, Begall S, Koubek P, Novakova P, Burda H. Directional preference max enhance hunting accuracy in foraging foxes. Biol Lett, 2011, 7:355-357
Hart V, Novakova P, Malkemper EP, Begall S, Hanzal V, Jezek M, Kusta T, Nemcova V, Adamkova J, Benediktkova K, Cerveny J, Burda H. Dogs are sensitive to small variations of the Earth´s magnetic field. Frontiers Zoology, 2013, 10:80
Eder SHK, Cadiou H, Muhamad A, McNaughton PA, Kirschvink JL, Winklhofer M. Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells. PNAS, 2012, 109:12022-12027
Effects of ELF electric and magnetic fields in (dairy) cows:
Algers B, Hultgren J. Effects of long-term exposure to a 400 kV, 50 Hz transmission line on estrous and fertility in cows. Prev Vet Med, 1987, 5:21-36
Algers B, Hennichs K. The effect of exposure to 400 kV transmission lines on the fertility of cows. Prev Vet Med, 1985, 3:351-361
Angell RF, Schott MR, Raleigh RJ, Bracken TD. Effects of a high-voltage direct-current transmission line on beef cattle production. Bioelectromagnetics, 1990, 11:273-282
Broucek J, Uhrincat M, Sandor A, Arave CW, Mihina S, Waiblinger S, Hanus A, Kisac P. Effect of low magnetic field on calves during prenatal development. Tierärztl Umschau, 2002, 57:241-248 (German)
Broucek J, Sandor A, Arave CW, Mihina S, Waiblinger S, Uhrincat M, Hanus A, Tancin V, Kisac P. Effect of low magnetic field on dairy cows. Tierärztl Umschau, 2001, 56:364-369 (German)
Stelletta C, De Nardo P, Santin F, Basso G, Michielotto B, Piccione G, Morgante M. Effects of exposure to extremely low frequency electro-magnetic fields on circadian rhythms and distribution of some leukocyte differentiation antigens in dairy cows. Biomed Environ Sci, 2007, 2:164-170
Burchard JF, Nguyen DH, Richard L, Block E. Biological effects of electric and magnetic fields on productivity of dairy cows. J Dairy Sci, 1996, 79:1549-1554
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Burchard JF, Nguyen DH, Richard L, Young SN, Heyes MP, Block E. Effects of electromagnetic fields on the levels of biogenic amine metabolites, quinolinic acid, and beta-endorphin in the cerebrospinal fluid of dairy cows. Neurochem Res, 1998, 23:1527-1531
Burchard JF, Nguyen DH, Block E. Progesterone concentrations during estrous cycle of dairy cows exposed to electric and magnetic fields. Bioelectromagnetics, 1998, 19:438-443
Burchard JF, Nguyen DH, Block E. Macro- and trace element concentrations in blood plasma and cerebrospinal fluid of dairy cows exposed to electric and magnetic fields. Bioelectromagnetics, 1999, 20:358-364
Rodriguez M, Petitclerc D, Nguyen DH, Block E, Burchard JF. 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. J Dairy Sci, 2002, 85:2843-2849
Burchard JF, Monardes H, Nguyen DH. Effects of 10 kV, 30 µT, 60 Hz electric and magnetic fields on milk production and feed intake in nonpregnant dairy cattle. Bioelectromagnetics, 2003, 24:557-563
Rodriguez M, Petitclerc D, Burchard JF, Nguyen DH, Block E, Downey BR. Responses of the estrous cycle in dairy cows exposed to electric and magnetic fields (60 Hz) during 8-h photoperiods. Anim Reprod Sci, 2003, 77:11-20
Rodriguez M, Petitclerc D, Burchard JF, Nguyen DH, Block E. Blood melatonin and prolactin concentrations in dairy cows exposed to 60 Hz electric and magnetic fields during 8 h photoperiods. Bioelectromagnetics, 2004, 25:508-515
Burchard JF, Nguyen DH, Monardes HG, Petitclerc D. Lack of effect of 10 kV/m 60 Hz electric field exposure on pregnant heifer hormones. Bioelectromagnetics, 2004, 25:308-312
Nguyen DH, Richard L, Burchard JF. Exposure chamber for determining the biological effects of electric and magnetic fields on dairy cows. Bioelectromagnetics, 2005, 26:138-144
Burchard JF, Nguyen DH, Rodriguez M. Plasma concentrations of thyroxine in dairy cows exposed to 60 Hz electric and magnetic fields. Bioelectromagnetics, 2006, 27-553-559
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Effects of stray voltage in cows
Erdreich LS, Alexander DD, Wagner ME, Reinemann D. Meta-analysis of stray voltage on dairy cattle. J Dairy Sci, 2009, 92:5951-5963
Hillman D, Stetzer D, Graham M, Goeke CL, Mathson KE, VanHorn HH, Wilcox CJ. Relationship of electric power quality to milk production of dairy herds – Field study with literature review. Sci Total Environ, 2013, 447:500-514
Effects of radiofrequency fields in cows:
Stärk KD, Krebs T, Altpeter E, Manz B, Griot C, Abelin T. Absence of chronic effect of exposure to short-wave radio broadcast signal on salivary melatonin concentrations in dairy cattle. J Pineal Res, 1997, 22:171-176
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Investigations on the impact of exposure to electromagnetics fields from mobile phone base stations on health, production, and behavior of cattle
Untersuchungen zum Einfluss elektromagnetischer Felder von Mobilfunkanlagen auf Gesundheit, Leistung und Verhalten von Rindern
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