Premium
Sensitivity of Goats to a Light Pulse During the Night as Assessed by Suppression of Melatonin Concentrations in the Plasma
Author(s) -
Deveson Sharon L.,
Arendt Jospehine,
Forsyth Isabel A.
Publication year - 1990
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1990.tb00677.x
Subject(s) - melatonin , darkness , photoperiodism , zoology , light intensity , radioimmunoassay , endocrinology , intensity (physics) , medicine , chemistry , biology , optics , physics
This study investigates the ability of a 1 h light pulse of different intensities at night to suppress plasma melatonin in goats. Six female Saanen dairy goats, about 2 yr old, were housed in a light‐tight shed. The goats were habituated for 1 wk to an 8L: 16D photoperiod (40.70 ± 4.16 μW/cm 2 ; 137 ± 14 lux), lights on 0800 h. A 1 h light pulse, of different intensity on each occasion, was given from 1900 to 2000 h. Light intensity was measured by using a lux meter (mean of 36 measurements at goat's eye level). Five different light intensities were given during December in the order 4.22 ± 0.62 μW/cm 2 (14.2 ± 2.1 lux), 0.68 ± 0.09 μW/cm 2 (2.3 ± 0.3 lux), 0.26 ± 0.004 μW/cm 2 (O.87 ± 0.14 lux), darkness, 40.70 ± 4.16 μW/cm 2 (137 ± 14 lux), with 1–3 d between treatments. The goats were bled hourly from 1500 to 1900 h and every 15 min from 1900 to 2100 h, and a last bleed occurred at 2200 h. Dark‐phase samples were taken in dim red light (<0.03 μW/cm 2 ; 0.1 lux). Plasma was assayed for melatonin by radioimmunoassay. Suppression of melatonin concentrations increased as light intensity increased as follows: Darkness, 0%; 0.26 ± 0.004 μW/cm 2 ; 0%; 0.68 ± 0.09 μW/cm 2 ; 43.1%; 4.22 ± 0.62 μW/cm 2 , 71.1%; 40.70 ± 4.16 μW/cm 2 , 81.2%. Suppression was significant ( P <0.05) at light intensities >0.68 μW/cm 2 , 2.3 lux. A hyperbolic relationship existed between percent suppression and light intensities.