Circadian Rhythm of the Preovulatory Surge of Luteinizing Hormone and Its Relationships to Rhythms of Body Temperature and Locomotor Activity in Turkey Hens1

Abstract

Simultaneous measurements of plasma LH, body temperature, and locomotor activity were made in laying turkey hens and are reported. Blood samples were remotely collected using a jugular cannula system, and body temperature and locomotor activity were remotely monitored using a radiotelemetry system in freely moving laying turkeys. Under a photoschedule of 14L:10D, the period for preovulatory surges of LH was 25.7 +/- 0.4 h while the periods for peak 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, and 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 constant light, initiation of LH surges had dispersed throughout the 24-h subjective day and night. With constant light, the amplitude of the peak body temperature rhythm decreased, while the duration of the locomotor activity rhythm became broadened and, in some birds, disorganized. Peak body temperature and onset of locomotor activity rhythms and LH surges did not coincide, even though peak body temperature, onset of locomotor activity, and LH surges had similar periods. It is concluded that 1) the photoschedule influences the periods of the LH surge, peak body temperature, and onset of locomotor activity; and 2) a specific or direct relationship between the rhythms of LH surge, body temperature, and locomotor activity remains to be determined in laying turkey hens.

Interval Between Preovulatory Surges of Luteinizing Hormone Increases Late in the Reproductive Period in Turkey Hens1

“…Continuous lighting was used in the current study to allow free running of the circadian rhythm of LH and P 4 preovulatory surges [18]. In chicken hens, ovulation and oviposition times start to free run within a day or two of when hens are treated with continuous light, and become distributed over the 24-h solar day within 7-10 days [19,27,35].…”

“…In chickens, the period of the circadian rhythm of oviposition time has been reported to be line dependent [27]. In turkeys, the circadian rhythm of LH surges has been reported to free run under continuous lighting [18], with the interval between surges being line dependent [1].…”

“…Then 16 laying hens were selected randomly, housed in individual cages as described for the Early hens, and switched to continuous light (24L:0D). The hens were given continuous light for 2 wk to allow the circadian rhythm of LH surges to free run [18,27] before and during collection of serial blood samples. Egg production was recorded daily before cannulation and then 3 times a day during the 10 days of serial bleeding.…”

“…Direct evidence for LH surge secretion controlling ovulation in birds is given by in vivo studies in which injection of exogenous LH in acutely hypophysectomized laying chicken hens induced single or multiple ovulations of hierarchical follicles [16,17]. Examination of several hundred LH and P 4 preovulatory surges [1,11,18] has shown that they are, without exception, coincident in laying turkey hens.…”

Socially induced ovulation synchrony and its effect on seabird population dynamics

“…Mammals and birds experience a surge of luteinizing hormone (LH) before each ovulation in a periodic fashion [31]. In women, LH surges approximately every 28 days; in domestic fowl, LH surges every 24 h during the laying season [14].…”