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LUTEINIZING HORMONE CONCENTRATIONS IN THE PLASMA OF LAYING HENS EXPOSED TO A 27-HR CYCLE OF LIGHT AND DARKNESS

Summary.: The time of peak concentration of LH in the peripheral plasma of ten laying hens kept on a 14 hr light/13 hr dark cycle was determined by radioimmunoassay. A single peak of LH occurred in each hen 3 hr before oviposition or 4 hr before ovulation. These are similar intervals to those reported for laying hens kept on a 14 hr light/10 hr dark cycle. The mean time of the observed peak in plasma LH was 2 hr 9 min after the beginning of the dark period. This is about 3 hr earlier than corresponding LH peaks reported for hens under normal lighting.