Transient hypothyroidism reinitiates egg laying in turkey breeder hens: termination of photorefractoriness by propylthiouracil

Department of Poultry Science, North Carolina State University, Raleigh 27695-7608, USA.

A study was conducted to determine the effects of transient hypothyroidism induced by propylthiouracil (PTU) on termination of photorefractoriness and reinitiation of lay in turkey breeder hens. The PTU was given for 6- or 8-wk periods via the feed and at various doses to yearling hens that had been continuously exposed to long photoperiods [16 h light (L):8 h dark (D)] for at least 25 wk. There was a dose-dependent cessation of lay as well as deletion of thyroxine (T4) and triiodothyronine (T3) during the treatment period. Hens receiving 0.1% PTU or more had little or no circulating thyroid hormones after 2 wk of treatment. Furthermore, resumption of a normal rate and duration of egg laying occurred following withdrawal of the PTU, without any changes in photoperiod. However, this effect only occurred in those hens that had received PTU doses of 0.1% or more and only when the treatment had been given for greater than 6 wk. The resumption of normal levels of egg laying occurred in the absence of a typical preceding molt. Body weights, livability, and fertility and hatchability of eggs from these hens were similar to those of controls. Clearly, turkey hens can be effectively recycled by pharmacological manipulation of the thyroid gland and the results are supportive of thyroid hormone(s) involvement in maintaining photorefractoriness in turkey hens.

This article has been cited by other articles:

				T. D. Siopes and J. A. Proudman Exposure duration to long day lengths associated with the expression of photorefractoriness in turkey breeder hens Poult. Sci., January 1, 2009; 88(1): 191 - 198. [Abstract] [Full Text] [PDF]

				T. D. Siopes Lighting for Summer Egg Production by Turkeys: Day Length and Light Intensity Poult. Sci., November 1, 2007; 86(11): 2413 - 2419. [Abstract] [Full Text] [PDF]

				J. A. Proudman and T. D. Siopes Potential Role of Thyroid Hormones and Prolactin in the Programming of Photorefractoriness in Turkey Hens Poult. Sci., August 1, 2006; 85(8): 1457 - 1461. [Abstract] [Full Text] [PDF]