The Effect of Intensity and Duration of Light on Photorefractoriness and Subsequent Egg production of Chukar Partridge

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Abstract
Three photoperiodic experiments on egg production of chukar partridge (Alectoris graeca chukar) were conducted under controlled environmental conditions. In test 1 the photorefractoriness of blind, thyroidectomized and intact chukars to long days (LD16:8) was examined from hatch until 123 weeks of age. Thereafter, the effects of long days of low intensity light (4 lux) on terminating the refractory period were observed. In the second test, the minimum level of light intensity to induce egg laying in chukars was determined at 64 and 103 weeks of age. In addition, the effect of step-wise increases in light intensity on egg production and photorefractoriness was compared to steady levels of light intensity. In the third test, 2 consecutive egg laying cycles were induced in blinded and intact chukars. Again the threshold level of light intensity to induce egg laying was determined. In addition, the effects of larger changes in intensity (10x) in terminating photorefractoriness were determined. The results indicate the following: 1) neither blinding nor thyroidectomy alters photorefractoriness; 2) either exposure to short daylengths or to low light intensity is necessary to break photorefractoriness before chukars can be photostimulated into egg production by long days; 3) the minimum light intensity for egg production is 2 lux; 4) chukars possess extraretinal photoreceptor(s) which respond to changes in both day length and intensity; 5) small changes in light intensity (2-5x) have little effect in terminating photorefractoriness; 6) 10x changes in intensity suppress photorefractoriness and allows an increase in both the duration of lay and the number of eggs.