“Chrono-functional milk”: The difference between melatonin concentrations in night-milk versus day-milk under different night illumination conditions

Abstract

Pineal melatonin (MLT) is produced at highest levels during the night, under dark conditions. We evaluated differences in MLT-concentration by comparing daytime versus night time milk samples, from two dairy farms with different night illumination conditions: (1) natural dark (Dark-Night); (2) short wavelength Artificial Light at Night (ALAN, Night-Illuminated). Samples were collected from 14 Israeli Holstein cows from each commercial dairy farm at 04:30 h ("Night-milk") 12:30 h ("Day-milk") and analyzed for MLT-concentration. In order to study the effects of night illumination conditions on cows circadian rhythms, Heart Rate (HR) daily rhythms were recorded. MLT-concentrations of Night-milk samples from the dark-night group were significantly (p < 0.001) higher than those of Night-illuminated conditions (30.70 ± 1.79 and 17.81 ± 0.33 pg/ml, respectively). Interestingly, night illumination conditions also affected melatonin concentrations at daytime where under Dark-Night conditions values are significantly (p < 0.001) higher than Night-Illuminated conditions, (5.36 ± 0.33 and 3.30 ± 0.18 pg/ml, respectively). There were no significant differences between the two treatments in the milk yield and milk composition except somatic cell count (SCC), which was significantly lower (p = 0.02) in the Dark-Night group compared with the Night-Illuminated group. Cows in both groups presented a significant (p < 0.01) HR daily rhythm, therefore we assume that in the night illuminated cows feeding and milking time are the "time keeper", while in the Dark-night cows, HR rhythms were entrained by the light/dark cycle. The higher MLT-concentration in Dark-night cows with the lower SCC values calls upon farmers to avoid exposure of cows to ALAN. Therefore, under Dark-night conditions milk quality will improve by lowering SCC values where separation between night and day of such milk can produce chrono-functional milk, naturally rich with MLT.

Melatonin concentration in cow’s milk and sources of its variation

“…They reported a mean production of 25 L milk/ day in the winter season (June) and found that the melatonin concentrations were 39.43 and 4.03 pg/mL in the milk sampled after milking at 2 am and 3 pm, respectively. Asher et al (2015), who studied cows that produced 34.34 ± 1.34 L milk/day, reported an average melatonin concentration of 30.70 ± 1.79 pg/mL in the milk when cows were kept for 13 h under 5.08 ± 0.04 lux of light with a wavelength of 648 ± 5.12 nm. Valtonen et al (2001) recorded melatonin levels of 56.4 pg/mL milk when the cows were kept for 17 h in the dark.…”

“…A short light wavelength decreases melatonin synthesis (Cajochen et al 2005;Asher et al 2015). The wavelength determines the perceived visual colour, which ranges from approximately 390 nm (purple colour) to 780 nm (red colour) in humans (Sjaastad et al 2010).…”

“…The number of hours of darkness and the photoperiod also dramatically affect synthesis (Dahl 2010). In addition, melatonin biosynthesis is sensitive to light wavelength because synthesis is suppressed by short light wavelengths (Cajochen et al 2005;Asher et al 2015).…”

“…Melatonin is produced under dark conditions and only has a half-life of about 30 min (Singh et al 2011). Therefore, milking time can affect the concentration of melatonin in milk (Milagres et al 2014;Asher et al 2015). In some countries, milk from night milking is rich in melatonin and has been commercialized as a sleep aid for people, such as Lullaby Milk in Ireland, Sleepiz and iNdream3 in New Zealand, Ingman Dairy's Night Time Milk in Finland, and Dreamerz in the United States (Boland 2010).…”

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

“…Although many studies were done on the topic of melatonin in rodents and ungulates, as species belonging to these groups are often used as model animals in chronobiological research, only 11 studies were identified as relevant to this review (Tables 2 and 5A,B). These records included seven rodent studies and four ungulate studies, which were performed on four rodent species (mice [105], rats [106][107][108], Siberian hamster (Phodopus sungorus) [109,110], and fat sand rat (Psammomys obesus) [111] and four ungulate species (cow [112], goat [113], sheep [114], and horse [115]). These records included nocturnal and diurnal species (the four ungulate and one rodent species, the fat sand rat).…”