Inhibition of nighttime melatonin secretion in cattle: threshold light intensity for dairy heifers

Abstract

Five pre-pubertal Holstein heifers were exposed for 16 h to a light intensity of 400 lx and thereafter to intensities of 0, 50, 100, 200, or 400 lx for an additional 8 h (5 x 5 Latin square design). Exposure to all intensities inhibited (P < 0.05) melatonin secretion for the initial few hours (of the 8-h exposure period); melatonin concentration subsequently increased, particularly with the lower light intensities. Only the highest light intensity (400 lx) suppressed (P < 0.05) plasma melatonin concentrations for the entire 8-h exposure period. Key words: Threshold, supplemental, light, intensity, inhibition, melatonin, heifer

Plasma melatonin and insulin‐like growth factor‐1 responses to dim light at night in dairy heifers

“…Previously, it was shown that exposure of cattle to light intensities >400 lx abolished the nocturnal rise in plasma melatonin [9, 21] and one 8‐hr exposure to light of 50 lx suppressed dairy heifer NML by 70% for the first 2–3 hr of the night [6]. We have now shown that light intensities of 10 or 5 lx do not suppress NML levels in heifers.…”

“…Previous lighting history (preconditioning) influenced sensitivity to light during the night in squirrels [25] in that squirrels raised and maintained under artificial light (700–1100 lx) during the day had 100% suppression in NML with 1360 lx, but captured wild squirrels adapted to natural day light (122,400 lx) required >1360 lx for 100% suppression of NML. Because daytime light intensity in the present study was 50% that of our previous study [6], it was expected that sensitivity to light would be greater in the present study but the opposite was the case. The use of incandescent fixtures for night‐light treatments in the present study may have attenuated the suppressive effect of 50 lx on NML because incandescent bulbs have low blue and green colour spectrum compared with fluorescent bulbs [26].…”

“…As found previously, the suppressive effect of 50 lx on NML did not persist to the fourth hour of the night period in the present study. Light intensities of 100 [6], 200 [6] and ≥ 400 lx [6, 21] maintained at least some suppressive effects on NML for the entire night treatment period in dairy heifers. Light threshold studies with other species (2–5) have involved only a short window of exposure (≤1 hr) during the night and thus sustainability of the NML suppression was not examined.…”

“…The lowest intensity of light (threshold intensity) to cause a significant suppression in night pineal or plasma melatonin level (NML) varies among species: 1.0 lx in the Syrian hamster [2] and sheep [3]; 2.3 lx in the goat [4], and between 500 and 1500 lx in humans [5]. A light intensity of 50 lx suppressed NML by 70% in dairy heifers and higher light intensities had greater suppressive effects [6]. However, the light intensity threshold that affects melatonin secretion in cattle is not known [7].…”

Effects of evening feeding and extended photoperiod on growth, feed efficiency, live animal carcass traits and plasma prolactin of beef heifers housed outdoors during two Manitoba winters

“…Survey results by Reksen et al (1999) indicated that extended photoperiod using low intensity (mean = 36 lux, range = 4 to 160 lux) light increased milk production of dairy cows. As well, light of 50 lux intensity was adequate to inhibit night-time release of melatonin in dairy heifers (Lawson and Kennedy 2001). Plasma PRL is often used as an indicator of the physiological impact of EP (Petitclerc et al 1983, Stanisiewski et al 1984.…”