Effects of exogenous melatonin and photoperiod on sexual maturation in pullets

Abstract

Hy-Line Gray commercial pullets were maintained under 8-h photoperiods, 16-h photoperiods and 16-h photoperiods supplemented with a diet containing 20 or 200 mg/kg melatonin (MEL) to investigate the role of MEL in sexual development. A total of 256 Hy-Line Gray commercial pullets were placed, four birds to a cage, in four similar light-proof rooms (8-h photoperiod) at 6 weeks of age. At 70 day, three rooms containing a total of 192 birds were transferred to a 16-h photoperiod, whereas 64 birds were maintained under the 8-h photoperiod. Diets containing MEL at 20 and 200 mg/kg were fed to birds in two of the rooms under 16-h photoperiods. Birds maintained under an 8-h photoperiod matured 11.25 day later than those maintained under a 16-h photoperiod (p < 0.05). The group of birds receiving 20 mg/kg MEL matured 1.19 day later than those maintained under the 16-h photoperiod and 10.06 day earlier than those maintained under the 8-h photoperiod. The group of birds receiving 200 mg/kg MEL matured 3.13 day later than those maintained under a 16-h photoperiod and 8.12 day earlier than those maintained under an 8-h photoperiod. The average body weight of birds maintained under the 8-h photoperiod was greater than that of birds maintained under the 16-h photoperiod (p < 0.05) and was similar between the different MEL groups. The abdominal fat weight was lower in 16L:8D group compared with 8L:16D group (p < 0.05). The concentrations of follicle-stimulating hormone, luteinizing hormone, oestrogen and insulin did not differ significantly among the groups. The melatonin concentration in 200 mg/kg melatonin group was higher than that observed in the other groups; however, this concentration did not differ significantly (p > 0.05). These data suggest that the birds did not perceive the final 8-h photoperiod as being part of the night when they were given the MEL diets; continuously high plasma MEL was not observed in birds that responded as if they were in constant darkness. However, the later maturity of the groups administered MEL diets compared with the groups maintained under a constant 16-h photoperiod clearly indicated that MEL has some influence on the sexual maturity of pullets.

Effects of Duodenal 5-Hydroxytryptophan Perfusion on Melatonin Synthesis in GI Tract of Sheep

“…For example, it improves the meat quality and quantity of cashmere goats [ 13 , 14 ], reduces somatic cell count and mastitis in dairy cattle to improve the quality of the milk [ 15 , 16 ]. Currently, in husbandry industrial, the methods used to regulation of MT levels in animals are primarily to alter the light/dark cycle of the environments [ 17 , 18 ], or by implantation [ 19 , 20 ], injection [ 21 ], and oral administration [ 22 ] of MT. As to the exogenous melatonin administration, several factors should be considered including its bioavailability, acting duration, economic benefit, and delivery methods [ 22 ].…”

Melatonin Administration Methods for Research in Mammals and Birds

“…Most, but not all, researchers dissolve melatonin crystalline powder in ethanol and dilute the solution in drinking water (Guyomarc’h et al, 2001; Heigl and Gwinner, 1995; Kumari et al, 2015) or mix it with food and let the ethanol evaporate (Chen et al, 2016; Lewis et al, 2006). Researchers who dissolve melatonin crystalline powder in ethanol should note that ethanol consumption rapidly and robustly suppresses plasma melatonin (Ekman et al, 1993) and salivary melatonin (Rupp et al, 2007) in a dose-dependent manner.…”

“…The dosage of orally administered melatonin corresponds to detectable increases in plasma melatonin, which suggests that dosage has a linear relationship with absorption through the digestive tract. However, in the animal studies reviewed here, only Chen et al (2016) administered more than one dose and measured circulating levels. Researchers should test if different doses of an orally administered hormone correlate with circulating levels of the hormone.…”

BMAL1 but not CLOCK is associated with monochromatic green light-induced circadian rhythm of melatonin in chick pinealocytes

“…In birds, pinealectomy abolished the circadian patterns of locomotor activity and body temperature (4, 5), which was attributed to the absence of the rhythmic secretion of melatonin, as cyclic melatonin administration restored the circadian rhythmicity of the pinealectomised birds (6, 7, 8). The change in the duration of melatonin production serves as a biological signal for the organisation of light-dependent functions, such as reproduction and behaviour (9, 10, 11). Light seems to play a definitive role in the rhythmic secretion of melatonin (12, 13).…”