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Identification of the blue light intensity administered to one eye required to suppress bovine plasma melatonin and investigation into effects on milk production in grazing dairy cows
Murphy, Barbara A. Herlihy, Mary M. Nolan, Margaret B. O'Brien, Christiane Furlong, John G. Butler, Stephen T.
Murphy, Barbara A.
Herlihy, Mary M.
Nolan, Margaret B.
O'Brien, Christiane
Furlong, John G.
Butler, Stephen T.
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2021-08
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Murphy BA, Herlihy MM, Nolan MB, O'Brien C, Furlong JG, Butler ST. Identification of the blue light intensity administered to one eye required to suppress bovine plasma melatonin and investigation into effects on milk production in grazing dairy cows. Journal of Dairy Science 2021;104(11):12127-12138; doi https://doi.org/10.3168/jds.2021-20526.
Abstract
Long-day photoperiod is known to positively affect
milk production in confinement dairy systems, and it
has been hypothesized that pineal melatonin (MT)
secretion plays a substantial role in this process. Specialized
mammalian photoreceptors that regulate MT
secretion are optimally stimulated by short wavelength
blue light. We investigated the blue light intensity
administered to one eye required to suppress MT secretion
in nonlactating dairy cows, and subsequently
examined effects on milk production in grazing dairy
cows. Following a 14-d light-dark 8:16 h environmental
conditioning period, 5 nonlactating Holstein-Friesian
cows were exposed to treatments of <1, 70, 125, 175,
and 225 lx for 8 additional hours using a 5 × 5 Latin
square design. Light was administered via headpieces
fitted with light-emitting diodes emitting blue light
(465 nm) to the right eye. All cows were then exposed
to a light-dark 16:8 h cycle for one night via the indoor
lighting system (>200 lx white light). Plasma samples
collected at regular intervals were assayed for MT. A
dose-dependent effect of light treatment on mean circulating
MT concentrations (and 95% CI) was observed
[9.4 (7.2, 12.3), 5.0 (3.8, 6.6), 4.4 (3.3, 5.7), 3.3 (2.5,
4.3) and 1.7 (1.3, 2.3) ng/mL for treatments of 0, 70,
125, 175, and 225 lx, respectively. Only the 225 lx treatment
acutely suppressed plasma melatonin concentration
to levels similar to the light-dark 16:8 h treatment
[1.9 (1.4, 2.5) ng/mL]. Forty spring-calving cows were
blocked on parity, calving date and Economic Breeding
Index for milk production and assigned to the control
treatment or blue light to a single eye (LT) treatment
from calving through 32 wk of lactation. The cows
assigned to LT treatment were fitted with headpieces
providing 225 lx of blue light to the right eye from
1700 until 0000 h. Mean milk production (and 95% CI)
during 32 wk of lactation was not affected by treatment
[20.3 (19.3, 21.3) vs. 20.9 (19.8, 22.0) kg/d, control and
LT, respectively]. Within multiparous cows, a treatment
by week interaction was detected, whereby LT
treatment increased milk production during the first 12
wk of lactation [25.8 (24.3, 27.3) vs. 28.0 (26.5, 29.5)
kg/d; +8.5%], but had no effect thereafter. Treatment
did not affect plasma insulin-like growth factor 1. We
identified the blue light intensity to one eye required to
acutely suppress MT concentrations. Transient favorable
effects on milk production were observed in multiparous
cows. It remains unclear how single-eye blue
light treatment affects galactopoiesis in grazing dairy
cows, and further research is needed to explore whether
this modality of light delivery represents a useful means
to aid productivity in pasture-based dairy systems.
Key words: melatonin, photoperiod, blue light, milk
production, insulin-like growth factor