Photostimulated Prolactin Release in the Turkey Hen: Effect of Ovariectomy and Environmental Temperature K. Gahali,* M. E. El Halawani,† ,1 and I. Rozenboim‡ * Animal Production Department, Faculty of Agriculture, Minia University, Minya, Egypt; † Department of Animal Science, University of Minnesota, St. Paul, Minnesota 55455; and ‡ Department of Animal Science, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel Accepted July 25, 2001 Ambient temperature modulates prolactin (PRL) secretion in birds. It is not known whether this modulation directly affects the PRL controlling mechanism(s) or whether it in- directly influences them through the onset of sexual matu- rity and/or the onset of incubation behavior. These experi- ments were designed to investigate the effect of elevated (32°) and reduced (10°) ambient temperatures on PRL se- cretion. Somatically mature, ovariectomized female turkeys were used to avoid the confounding effects of reproductive stage, nesting, and egg stimuli on PRL secretion. Hens were ovariectomized 5 weeks before, on the day of, or 10 days after the inception of photostimulation. Temperature treat- ments included chronic exposure (5 weeks) to 32 or 10° and acute exposure (i.e., temperature was reversed from 32 to 10° or from 10 to 32° on or after the day of photostimula- tion). Chronic exposure to either 32 or 10° had no effect on the rise in serum PRL that followed photostimulation in both sham-operated controls and ovariectomized hens. Acute exposure to 10 or 32° altered the photoperiodically stimulated rise in plasma PRL. Birds switched from 10 to 32° showed a significantly greater PRL increase than birds shifted from 32 to 10°. Ovariectomy enhanced the PRL re- sponse to the gonadal stimulating photoperiod. The effect was most pronounced in hens photostimulated prior to ovariectomy. These findings suggest that ambient tempera- ture and/or ovariectomy have a modulating effect on the PRLresponse to long days. © 2001 Academic Press Key Words: turkey; prolactin; ovary; ovarian steroids; photostimulation; high and low ambient temperatures; ovariectomy. INTRODUCTION In gallinaceous birds, the onset of gonadal recrudes- cence in response to increasing day length is associ- ated with increases in circulating prolactin (PRL) lev- els and PRL gene expression (El Halawani and Rozenboim, 1993). This PRL response appears to be a direct function of the changing day length. Thereafter, the PRL level is related to the stage of the reproductive cycle, with further increases occurring around the on- set of sexual maturity (Etches and Cheng, 1982; El Halawani et al., 1983). This PRL rise can be prevented by ovariectomy (OVX) (El Halawani et al., 1983) and modulated by the presence of a nest or eggs (El Hala- wani et al., 1984). The dramatic increase in PRL asso- ciated with incubation behavior is well documented for several avian species (i.e., chicken, Sharp et al., 1979; turkey, Burke and Dennison, 1980). The steady state levels of PRL mRNA and PRL transcription have also been shown to reach their peak levels during the incubation phase of the reproductive cycle (Wong et al., 1991; Tong et al., 1997). Disruption of nesting ac- tivity leads to a decrease in circulating PRL levels and PRL gene expression (El Halawani et al., 1980; Proud- man and Opel, 1981; Tong et al., 1997). 1 To whom correspondence should be addressed at 495 AnSci/ VetMed, 1988 Fitch Avenue, St. Paul, MN 55108. Fax: (612) 625-2743. E-mail: elhal001@tc.umn.edu. General and Comparative Endocrinology 124, 166 –172 (2001) doi:10.1006/gcen.2001.7700, available online at http://www.idealibrary.com on 0016-6480/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved. 166