SECRETION OF LUTEINIZING-HORMONE DURING A FORCED MOLT IN TURKEY HENS

The secretory pattern of luteinizing hormone (LH) was determined in tu rkey hens during a forced molt induced by water (1 d) and feed (5 d) r estriction and switching the photoschedule from 14 h Light (L):10 h da rk (D) (long-day) to 6L:18D (short-day), the Ist d of feed and water r estriction. Serial blood samples were collected from six hens (every 1 0 min for 6 h, then every 4 min for 2 h) at four different times durin g the trial. The first serial bleeding was done at the end of egg layi ng and 1 d before forced molting was initiated; the second 7 d after t he 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 lighti ng and 2 d after returning the hens to long-day lighting. Egg producti on stopped by 5 d after initiation of forced molting. Egg production r einitiated by 34 d (range 22 to 34 d) after returning to long-day ligh ting. 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 ampl itude of pulses of LH were also low at these times. Overall and baseli ne 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 i nitiation of forced molting. At 2 d after switching to long-day lighti ng, increases in overall, baseline, and number of pulses of LH were de tected. 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 decreas e during a forced molt and subsequent reconditioning period. Relativel y large increases in circulating LH are induced by exposing the recond itioned hens to the long-day photoperiod. of 14L:10D, aid this increas e was associated with an increase in overall and baseline LH concentra tions and LH pulse frequency.