Department of Animal Science,
niversity of Minnesota, St. Paul, MN
U.S.A.
Our studies of the last three years have led to the novel findings suggesting that turkeys' egg laying activity is regulated by two light pathways, an inhibitory pathway and stimulatory pathway. Egg production is dependent upon the relative activation of the two pathways. The inhibitory pathway is activated by stimulating retinal photoreceptors by the green band of the spectrum, and the stimulatory pathway is activated by the direct action of the red band on photoreceptors in the brain. It is hypothesized that photostimulation of breeders with separate light sources, one stimulatory (red) and another inhibitory (green) will enable one to optimize the red/green band ratio as well as the stimulatory wavelength and its energy level to maximize egg production.
We investigated the effect of light spectra in the near- (630 nm) middle-(680 nm) and far-red (720 nm) of the spectrum on the reproductive performance utilizing LED Lamps. The average egg production during the 28-week experimental period were 56.77%, 60.71%, 56.63, and 48.39 for hens photostimulated with incandescent lamps (control), 630 nm, 680 nm, and 720 nm LED lamps, respectively. Hens which were photostimulated with the 630 nm LED lamps with an energy level of 273µw/cm2 had the best egg production.
Introduction
The photosexual responses and subsequent alterations in reproductive activities in birds have been shown to be mediated by retinal and extra-retinal (brain) photoreceptors. Birds subjected to a gonad stimulating photoperiods, long wave radiation (630-750 nm) penetrates the tissue and directly acts on hypothalamic extra-retinal photoreceptors to stimulate reproductive function (Benoit and Assenmacher, 1966, Menaker and Underwood, 1972). In contrast to the stimulatory effect of long wave radiation on reproductive activity, activation of retinal photoreceptors by visible radiation appears to be inhibitory to reproduction (Homma et al., 1972, Siopes and Wilson, 1980a, 1980b). The response to visible radiation is surmised to be mediated by the green-yellow bands of the light spectrum (545-575 nm), where the avian retina is maximally sensitive (Prescott and Wathes, 1999; Lewis and Morris 2000).
Taken together, the aforementioned findings lead to the following hypothesis: photostimulation with radiation in the red band of the spectrum (630- 750 nm) under minimum light intensity (brightness; minimum radiation in the green-yellow bands of the spectrum) will provide the greatest photostimulation effect and enhances egg production.
Experimental Procedures and Results
To test this hypothesis, hens were photostimulated by filtered light (Lee filters, Gopher Stage Lighting, MN, USA) from 60 watt incandescent lamps. The red light (red filter) had peak emission in the 650-725 nm range (565µw/cm2, 4.45 lx) and the green light (green filter) had peak emission between 500 to 575 nm (248 µw/cm2, 23.1 lx). The control group was photostimulated by white light (full spectrum provided by the 60 watt incandescent lamp, (13.4 W/cm2, 33.7 lx).
Control white and red light photostimulated groups showed a significant increase in plasma luteinizing hormone (LH) and (prolactin) PRL levels. The mean values of plasma PRL and LH in the green light group remained significantly below those of control white or red light hens. During the egg laying period, egg production of the control group which was photostimulated with the full light spectrum from the incandescent lamps declined at a faster rate than that of hens' photostimulated with the red band of the spectrum. The green light group exhibited different egg laying pattern than that of the control and the red light groups; their egg production remained consistently low throughout the experimental period. The total number of eggs per hen during the 27 week experimental period was 95.2, 84.0, and 28.2 eggs for red, control and green groups, respectively.
The data indicated that the predominance of energy from the red band improved egg production, whereas prevalence of the green band inhibited egg laying. Furthermore, these findings suggest that turkeys' egg laying activity is regulated by two light pathways, an inhibitory pathway and a stimulatory pathway. The inhibitory pathway is activated via the retina by the green band of the light spectrum and the stimulatory pathway is activated by the direct action of the red band on the photoreceptors in the brain. .
The width of the red band is between 630-750 nm. Previous studies with plants showed that the specific wavelength within the red band was highly critical for flowering of plants. We hypothesized that this might be the case for egg laying activity. The availability of LED diodes with specific wavelengths allowed us to design systems with different wavelengths that were tested experimentally and might be applied commercially for photo stimulating breeder turkeys.
To investigate the wavelength requirements within the red band of the spectrum for maximum egg production, lamps or panels were built with spectra in the near- (630 nm), middle- (680 nm), and far- red (720 nm) utilizing LED diodes. The three experimental light treatments were compared to control white light from incandescent lamps. The breeder flock completed a 28-week egg production period. Egg production of control hens that were photostimulated with incandescent lamps peaked at 5.58±0.21 (mean ±S.E.) eggs/hen/wk by the fourth week of photostimulation. There was an advance in peak egg production by one week when hens were photostimulated with 630 nm or 680 nm wavelengths from LED lamps. Peak egg production was somewhat higher for the 630 nm (5.91±0.15 eggs/hen/wk) and 680 nm (5.64±0.05 eggs/hen/wk) groups than that of the incandescent photostimulated control turkeys. Peak egg production of hens' photostimulated with 720 nm wavelength from LED lamps (5.47±0.14 eggs/hen/wk) was delayed one week when compared to that of hens' photostimulated with incandescent lamps. Thereafter, egg production declined with the advancement of the laying season.
However, the decline in egg production appeared to stabilize by Week 7. At this time, birds' photostimulated with 630 nm wavelength had better egg production persistency when compared to that of the incandescent control group or the 720nm group.
The average egg production during the 28-week laying period were 3.99±0.15, 4.25±0.15, 3.96±0.16 and 3.39±0.19 eggs/hen/wk for hens photostimulated with incandescent lamps, 630 nm, 680 nm, and 720 nm LED lamps, respectively. It is of interest to note that hens photostimulated with the 630 nm LED lamps laid significantly more eggs (7.28 eggs per hen) than their corresponding control incandescent hens. Also, the present results clearly show that further increase in the wavelength of the red band beyond the 630 nm has a significant negative correlation (-0.97; P<0.05) on egg production.
It is clear that breeder hens photostimulated with light spectrum at the 630 nm wavelength had better egg production as compared with those photostimulated with 680 and 720 nm wavelengths or full light spectrum from incandescent lamps. However, it is not known whether the amount of energy emitted by LED diodes is exceeding or below the level that is ideal for optimum egg production. It is possible that excess energy penetrating the brain may have detrimental effect on egg production and less energy may not be sufficient to maximize egg production. Accordingly we tested the effect 630 nm wavelength at three energy levels including 187, 273 and 460µw/cm2 on egg production.
Egg production of control hens that were photostimulated with incandescent lamps peaked at 5.45±0.12 (mean ± S.E.) eggs/hen/wk, by the fourth week of photostimulation. The highest peak production (5.86 eggs/hen/wk) was observed at the highest energy level (460 µw/cm2), on the third week of production. However, the overall average egg production during the 27 week period was greatest (4.01±0.13 eggs/hen/wk) at the 273 µw/cm2 energy level; followed by the 460 µw/cm2 (3.92±0.12 eggs/hen/wk), 187µw/cm2 (3.77±0.22 eggs/hen/wk) and hens photostimulated with incandescent lamps (3.49±0.12 eggs/hen/wk).
References
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- Siopes TD, Wilson WO. Participation of the eyes in the photosexual response of Japanese quail (Coturnix coturnix japonica). Biol Reprod 1980b; 23:352-357.
- Prescott NB, Wathes CM. Reflective properties of domestic fowl (Gallus g. domesticus), the fabric of their housing and the characteristics of the light environment in environmentally controlled poultry houses. Br Poult Sci 1999; 40:185-193.
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From Proceedings of the "Midwest Poultry Federation Convention", St. Paul, Minnesota, U.S.A.
