Circadian rhythm of the preovulatory surge of luteinizing hormone and its relationships to rhythms of body temperature and locomotor activity in turkey hens

Simultaneous measurements of plasma LH, body temperature, and locomotor act ivity were made in laying turkey hens and are reported. Brood samples were remotely collected using a jugular cannula system, and body temperature and locomotor activity were remotely monitored using a radiotelemetry system i n freely moving laying turkeys. Under a photoschedule of 14L: 10D, the peri od for preovulatory surges of LH was 25.7 +/- 0.4 h while the periods for p eak body temperature and onset of sustained locomotor activity were 24.9 +/ - 0.4 and 25.7 +/- 0.5 h, respectively. During exposure to constant light, the periods for preovulatory surges of LH, peak body temperature, and onset of sustained locomotor activity increased to 27.9 +/- 0.9, 26.7 +/- 0.7, a nd 27.4 +/- 0.7 h, respectively. With the 14L:10D photoschedule, initiation of LH surges was restricted to the scotophase, but after 8 days of constan t tight, initiation of LH surges had dispersed throughout the 24-6 subjecti ve day and night. With constant light, the amplitude of the peak body tempe rature rhythm decreased, while the duration of the locomotor activity rhyth m became broadened and, in some birds, disorganized. Peak body temperature and onset of locomotor activity rhythms and LH surges did not coincide, eve n though peak body temperature, onset of locomotor activity, and LH surges had similar periods. It is concluded that 1) the photoschedule influences t he periods of the LH surge, peak body temperature, and onset of locomotor a ctivity; and 2) a specific or direct relationship between the rhythms of LH surge, body temperature, and locomotor activity remains to be determined i n laying turkey hens.