Abstract:

To elucidate the molecular mechanism of monochromatic light on estrus in rabbits from the perspectives of behavior, vision and endocrine, the behavioral observation experiment was performed in an artificial light control room. A 6 m×6 m square slotted wooden floor platform was surrounded by open-door rabbit cages in a round shape. Six rabbit cages were placed on each side. Conventional nipples were placed in the cage. Drinking fountains and troughs, with LED strips installed 60cm above each side of the rabbit cage, projecting LED red (660 nm), green (540 nm), blue (480 nm), and white (400~760 nm) light down, the light intensity was 100 lx, and the duration was 12 h. The LED strip position was adjusted randomly once a week to ensure that the LED light color became the only variable. The camera recorded the selective stay behavior of female rabbits. In the light color test, 300 reserve female rabbits reared in a single cage under different LED light colors were randomly divided into 5 groups at random, with 3 repetitions in each group and 20 repetitions in each. LED red light (660 nm), LED green light (540 nm), LED blue light (480 nm) and LED white light (400-760 nm) were projected downward 60 cm above the rabbit cage. The control group was incandescent (400-1 050 nm). Female rabbits received supplementary light from Friday to Sunday evening from 18:00 to 06:00 the next day in the formal experiment, the duration was 12 h, with 7 d pre-experiment and 90 d positive trial period. The light intensity was 100 lx. Different LED light colors can affect the choice of the female rabbit’s activity space. The red LED environment was more easily accepted and stayed by the female rabbit. The frequency of stay was 13.1% and 11.6% higher than that of the LED green light and LED blue light, respectively. The concentrations of β-EP and 5-HT in the serum of reserve young female rabbits in LED red light and incandescent lamp groups were significantly higher than those in LED green light group and LED blue light group (P<0.05). Cortisol concentration in LED red light environment was significantly higher than that in LED green light group (P<0.05). Compared with the incandescent control group and the LED white light group, the estrus rate of female rabbits in the LED red light group increased by 20.89% and 10.51%, respectively, with significant differences (P<0.05). The expression of Opn4 gene in the retina of female rabbits in LED red light group was significantly higher than that in incandescent light group and LED green light group (P<0.05). Different LED light colors had an effect on the serum MLT content of female rabbits in a specific period of time (23:00—00:30). Compared with the LED green light group, the female rabbit serum MLT content in the red light group environment was 10.32% lower with a significant difference (P<0.05). Compared with LED white light, LED red light significantly inhibited the expression of Aanat mRNA in pineal cones (P<0.05). The expression of Mel1a mRNA in pineal gland of female rabbits in LED red light group was significantly higher than that in LED green light group and blue light group (P<0.05). During the periodical breeding and production of short-day sunshine in large-scale rabbit farms, three consecutive times per week, between 18:00—06:00, the use of 100 lx LED red light to supplement light can improve female estrus synchronization. LED red light can affect rabbit behavior and estrus synchronization through Opn4-MLT pathway.

Key words: LED light color, retina, pineal cone, estrus synchronization, molecular regulation