This study consisted of a series of experiments designed to test the hypothesis that exposure to extremely low frequency (ELF) electric and magnetic fields (EMF), similar to those generated by power transmission lines, can modify the response to photoperiod in dairy cows. Thirty two Holstein cows, 16 pregnant and lactating and 16 non-pregnant and non-lactating, maintained under short photoperiod (8 h light, 16 h dark), were exposed to an electric field of 10 kV/m and a magnetic field of 30 muTesla for 16 h/d, using cross-over experimental designs with three-period sequences. These exposure conditions resembled those prevalent under a 735 kV line carrying an extreme current load. Feed consumption, milk yield and composition, body weight, circulating concentrations of melatonin, prolactin, IGF-1 and growth hormone were assessed, as well as estrous cycle traits. A positive association was found between EMF exposure and feed consumption, uncorrected milk yield at the end of the exposure period and blood concentration of IGF-1. EMF exposure was also associated with an increase in blood prolactin concentration and decreased melatonin levels during the photophase in lactating pregnant cows. Non-lactating cows exposed to EMF showed longer estrous cycles. It was concluded that exposure to ELF EMF similar to those found under power transmission lines under extreme conditions of load elicits a biological response in dairy cows. Some aspects of this response are consistent with the hypothesis of a modification of the response to photoperiod.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.84426 |
| Date | January 2003 |
| Creators | Rodriguez, Maria A. (Maria Angeles), 1958- |
| Contributors | Downey, B. R. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Animal Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001984719, proquestno: AAINQ88570, Theses scanned by UMI/ProQuest. |
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