Abstract
The secretory pattern of luteinizing hormone (LH) was determined in turkey hens during a forced molt induced by water (1 d) and feed (5 d) restriction and switching the photoschedule from 14 h light (L):10 h dark (D) (long-day) to 6L:18D (short-day), the 1st d of feed and water restriction. Serial blood samples were collected from six hens (every 10 min for 6 h, then every 4 min for 2 h) at four different times during the trial. The first serial bleeding was done at the end of egg laying and 1 d before forced molting was initiated; the second 7 d after the start of forced molting and short-day lighting; the third after 49 d of short-day lighting, and the fourth after 56 d of short-day lighting and 2 d after returning the hens to long-day lighting. Egg production stopped by 5 d after initiation of forced molting. Egg production reinitiated by 34 d (range 22 to 34 d) after returning to long-day lighting. Overall and baseline concentrations of LH were low at the end of egg laying and 7 d after the start of forced molting. Number and amplitude of pulses of LH were also low at these times. Overall and baseline concentrations of LH remained low after 49 d of short-day lighting, with no change in number of LH pulses per 8 h. However, the amplitude of LH pulses was increased at this time in comparison to just after initiation of forced molting. At 2 d after switching to long-day lighting, increases in overall, baseline, and number of pulses of LH were detected. Peak amplitude did not change 2 d after switching to the long-day photoperiod. It was concluded that in turkey hens at the end of a relatively long laying period, baseline LH is low and does not decrease during a forced molt and subsequent reconditioning period. Relatively large increases in circulating LH are induced by exposing the reconditioned hens to the long-day photoperiod of 14L:10D, and this increase was associated with an increase in overall and baseline LH concentrations and LH pulse frequency.
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