title: Plasma melatonin and insulin-like growth factor-1 responses to dim light at night in dairy heifers.
abstract: The effect of dim (5, 10 and 50 1x) light at night on night plasma melatonin level (NML) and night plasma insulin-like growth factor-1 (IGF-1) level was determined in 12 prepubertal Holstein heifers (245 +/- 16 days age) using a 4 x 4 Latin Square design with 14-day treatment and 14-day recovery periods. Blood samples were collected at 23:00 hr (prior to the 8 hr night treatment which commenced at mid-night) on days 0, 3 and 13, and throughout the night at 01:00, 02:00, 03:00, 04:00, 06:00 and 08:00 hr on days 1, 4 and 14 of treatment. Plasma was analysed by radioimmunoassay for melatonin (all samples) and IGF-1 (samples for day 14, 04:00 hr only). Treatment (P = 0.03) and treatment x time (P = 0.02) were significant for NML. Exposure to 50 lx suppressed NML by 50% during the initial 2 hr of the night, but not thereafter. Exposure to 5 and 10 lx had no effect on NML. The NML response to 50 lx was found on all treatment days studied (treatment x time x day; P = 0.99). There was no treatment effect on plasma IGF-1 level (P = 0.89), but plasma IGF-1 level was higher (P = 0.001) during period 4. Plasma IGF-1 level and NML tended (P = 0.10) to be negatively correlated. Light intensities of 10 lx or less appear safe for use at night in dairy barns where darkness is recommended.
authors.affiliation: Department of Animal Science, University of Manitoba, Winnipeg, MB, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Muthuramalingam
authors.forename: A D
authors.initials: AD
authors.lastname: Kennedy
authors.forename: R J
authors.initials: RJ
authors.lastname: Berry
mesh_terms: D000818:Animals; D002417:Cattle; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008027:Light; D008550:Melatonin / Q000097:blood*; D010870:Pineal Gland / Q000528:radiation effects
chemical_list: D007334:Insulin-Like Growth Factor I; D008550:Melatonin