Photodermatol Photoimmunol Photomed 2000; 16: 178–182 Copyright C Munksgaard 2000 Printed in Denmark ¡ All rights reserved Munksgaard ¡ Copenhagen ISSN 0905-4383 Effects of a 2-week treatment with pulsed monochromatic light in healthy pigs: a clinical and morphological study M. Jensen-Waern 1 , S. Ekman 2 1 Unit for Comparative Physiology and Medicine, Departments of Large Animal Clinical Sciences and 2 Pathology, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden Background: Pulsed monochromatic light (PML) is now used clinically for pain relief and wound healing in both human and veterinary practice. The purpose of this study was to evaluated the clinical and path- ological effects of PML irradiation in an animal model, using healthy specific pathogen-free pigs. Methods: After 2 weeks of habituation, one group of animals (nΩ9) underwent treatment with pulsating monochromatic infrared and red light while the con- trol group (nΩ9) was left untreated. PML was given five times a week during a 2-week period, and at each treatment the total radiant exposure was 6.3 J/cm 2 . At the completion of the study, all pigs were subjected to complete necropsy. Results: None of the animals showed any clinical L ow-energy photon therapy (LEPT), including infrared and red pulsed monochromatic light (PML), has gained wide application and is now used for a number of indications, such as pain relief and wound healing, in both human and veterinary practice (1). Several scientific re- ports on the medical effects of LEPT and its possible in- duction of changes in the cell metabolism have been pub- lished (2–4). However, evaluations concerning toxic effects or side-effects have been sparse. The present study was therefore undertaken to deter- mine whether any clinical side-effects were evident after LEPT performed in a similar manner as that used in the treatment of pressure ulcers in humans. The study in- cluded a pathological examination which met the require- ments of international guidelines for medicinal products (5). The pig was chosen as an animal model because of its well-accepted physiological similarities to humans, and a 2-week treatment program with a moderate irradiation dose of PML with different pulsations and wavelengths (Biolight TM International AB) was applied. 178 signs of disease during the study period. The meas- ured hematological and clinico-chemical variables all showed values within the reference range and the daily weight gain was high in both the treatment and control groups (825 and 923 g/day, respectively). The path- ological examination revealed no morphological dif- ferences between treated and non-treated animals. Conclusion: In healthy pigs, no adverse effects of low- energy photon therapy on the clinical state of health or on the morphology of different tissues were ob- served. Key words: low-energy photon therapy; side-effects; pig; pathology. Material and methods Animals The experimental design was approved by the Ethics Committee for Animal Experiments, Uppsala, Sweden (C308/97). The study was performed on specific-pathogen free (SPF) pigs (Serogrisen A , Ransta, Sweden; 6). Two litters of 12-week-old hybrid (crossed Swedish Landrace and Swedish Yorkshire) pigs were randomly divided, num- bered, and two new groups were formed. At arrival, the mean weight of the pigs in the control group (C; nΩ9, three castrates and six sows) was 29.6 kg and that in the treatment group (T; nΩ10, five castrates and five sows) was 31.7 kg. The weight was measured weekly on an elec- tronic scale (Stathmos 5011, Jönköping, Sweden) and the daily weight gain was calculated for each week. The ani- mals were group-housed in pens with solid walls, a con- crete floor and straw beds, and fed ad libitum (Singel Flex A , Lantmannen, Sweden). During a 2-week period the pigs were habituated to their new environment and to the