Blindness in Smoky Joe roosters results in advanced sexual maturation

Transcription

1 Blindness in Smoky Joe roosters results in advanced sexual maturation Jennifer Perttula and Grégoy Y. Bédécarrats 1 Department of Animal and Poultry Science, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W. Received 7 May 2012, accepted 28 August Perttula, J. and Be de carrats, G. Y Blindness in Smoky Joe roosters results in advanced sexual maturation. Can. J. Anim. Sci. 92: In chickens, an increase in photoperiod activates the hypothalamo-pituitary gonadal axis resulting in sexual maturation. Although it is well established that light can directly stimulate the hypothalamus, the relative contribution of the eye in the control of reproduction is still controversial. Using a genetically blind line of chickens (Smoky Joe), we investigated the relative importance of the retina of the eye in sexual maturation in roosters. Furthermore, to evaluate the effect of photostimulation, three generations of blind and sighted Smoky Joe roosters were utilize. Generation 1 (G1) was photostimulated at 17 wk of age, while generation 2 (G2) was left un-photostimulated and generation 3 (G3) was photostimulated at 12 wk of age. Blind roosters in G1 and G2 matured between 17 and 19 wk of age (testicular weight, comb length) independently of photostimulation whereas maturation of sighted animals was significantly delayed in G2. However, this advanced sexual maturation was no longer evident when birds were stimulated at 12 wk of age. Blind roosters in G2 showed advanced spermatogenesis when compared with sighted animals. No significant difference in plasma testosterone levels was observed for any of the three generations. In conclusion, although still photosensitive, blind rooster sexually matured spontaneously earlier than their sighted counterpart. Key words: Avian, chickens, roosters, reproduction, blindness, maturation Perttula, J. et Be de carrats, G. Y La cécité chez les coqs Smoky Joe a pour effet d avancer la maturation sexuelle. Can. J. Anim. Sci. 92: Chez le poulet, une augmentation de la photope riode est ne cessaire pour stimuler l axe hypothalamo-hypophyso-gonadique responsable de la maturite sexuelle. Meˆme s il a e te prouvé que la lumie` re peut stimuler directement l hypothalamus, le roˆle joue par les yeux lors de la maturation sexuelle reste a` de montrer. Nous avons utilise une ligne e de poulets ge ne tiquement aveugles (Smoky Joe) pour de terminer l importance de la re tine lors du de veloppent sexuel chez le coq. De plus, pour e valuer l impact de la photostimulation, nous avons utilise trois géne rations de Smoky Joe, aveugles ou voyants. La premie` re ge ne ration (G1) a été photostimule e à l aˆge de 17 semaines, la deuxie` me ge ne ration (G2) n a pas été photo-stimule e alors que la troisie` me géne ration (G3) a e te stimule e à 12 semaines. Les coqs aveugles de G1 et G2 ont tous atteints la maturite sexuelle entre 17 et 19 semaines (poids des testicules, longueur de la creˆte) inde pendamment de la photostimulation alors que la maturation des animaux voyants de G2 était retardée. Par contre, cette diffe rence n e tait plus e vidente chez les oiseaux stimule s a` 12 semaines. La spermatogene` se chez les coqs aveugles de G2 e tait aussi avancée par rapport aux coqs voyants. Aucune diffe rence n a été observée sur les concentrations plasmatiques de testoste rone pour chaque ge ne ration. En conclusion, meˆme s ils sont photo-sensibles, les coqs aveugles ont une maturation sexuelle spontane e plus rapide que les coqs voyants. Mots clés: Espèce aviaire, poulet, coqs, reproduction, ce cite, maturation Most domestic avian species use light as an indicator to initiate and/or terminate reproduction. Increasing the photoperiod stimulates the secretion of gonadotropin releasing hormone (GnRH), which in turn induces the synthesis and release of gonadotropins [luteinizing hormone (LH) and follicle stimulating hormone (FSH)] by the pituitary gland (for review: Dawson et al. 2001; Sharp 2005). Increasing levels of LH and FSH then stimulate the development and maturation of the gonads. This activation of the reproductive axis appears to be mediated mostly via extra-retinal photoreceptors located within the hypothalamus, and the eye may have little if any role. As a matter of fact, studies have previously shown that ducks (Benoit 1964), house sparrows (Menaker and Keatts 1968; McMillan et al. 1975), Japanese quail (Oishi and Lauber 1973; Follett et al. 1975), white-crowned and golden-crowned sparrows (Gwinner et al. 1971) and chickens (Ookawa 1970; Harrison 1972) do not require their eyes to exhibit seasonal gonadal development. However, in addition to the stimulatory pathway, an inhibitory component involving gonadotropin inhibitory hormone (GnIH) has also been characterized (for review: Tsutsui et al. 2009) and its production was recently shown to be under the control of melatonin produced by the retina of the eye and the pineal gland (Ubuka et al. 2005; Chowdhury 1 Corresponding author ( gbedecar@uoguelph.ca). Abbreviations: FSH, follicle stimulating hormone; GnIH, gonadotropin inhibitory hormone; LH, luteinizing hormone Can. J. Anim. Sci. (2012) 92: doi: /cjas

2 484 CANADIAN JOURNAL OF ANIMAL SCIENCE et al. 2010). Unfortunately, investigating the response of reproductive organs to photoperiods often requires the use of invasive techniques such as ocular enucleation, suture of the eye lids or use of polypeepers (vision restriction devices) and, although these techniques have allowed for a greater understanding of how light is perceived by avian species, the relative contribution of retinal and extra-retinal photoreceptors remains unclear. Thus, to further investigate the impact of the retina on sexual maturation in roosters, we used a genetically blind strain of the white Leghorn chicken called Smoky Joe. The blindness phenotype, resulting from retinal degeneration, is carried by an uncharacterized autosomal recessive mutation (Salter et al. 1997). MATERIAL AND METHODS Animals To generate both blind and sighted individuals and to avoid inbreeding, three generations of Smoky Joe chickens were established by artificial insemination following a strict breeding plan based on pedigree. As the genetic mutation has still not been identified in this strain, breeding was performed based on phenotypic observations. The ontogeny and range of phenotypic anomalies have previously been described (Salter et al. 1997). From the parent stock, blind individuals were considered homozygous, while sighted individuals (females) were considered heterozygous if their progeny was mixed blind and sighted, and potentially homozygous sighted if their progeny was 100% sighted even when bred with blind males. Blind and sighted cockerels were raised together in mixed group floor pens until placed in individual battery cages for the experiments. Although some chicks were obviously blind at hatch (bulgy or sunken eyes), all affected individuals (homozygous) developed full blindness by 6 wk of age and status was verified by lack of pupillary light reflex. Birds were initially maintained under 24 h light for the first 2 wk of life, then the photoperiod was switched to 8 h. For generation 1 (G1), cockerels (n60; 30 blind and 30 sighted) were transferred to individual cages at 16 wk of age and photostimulated at 17 wk of age by an abrupt change to a 14-h photoperiod. Birds from generation 2 (G2) (n 50; 25 blind and 25 sighted) were also transferred to individual cages at 16 wk of age, but were then maintained under an 8-h photoperiod throughout (non-photostimulated). As initial results suggested blind birds may not be photosensitive, birds from a third generation (G3) (n60; 30 blind and 30 sighted) were transferred to individual cages and photostimulated at 12 wk of age with an abrupt change to a 14 h photoperiod. For all generations, light intensity was adjusted to 10 lx at birds level and was provided by incandescent bulbs. At placement, both blind and sighted birds were randomly assigned to individual cages and maintained in the same room. Animals were fed ad libitum a standard grower and breeder diets that met or exceeded NRC standards (1994). All procedures were reviewed and authorized by the University of Guelph Animal Care Committee. Testes Collection, Measurement of Body Weight and Comb Length Blind and sighted roosters from each generation were sacrificed at specific time points to monitor sexual maturation. Tissues were collected at 14, 17, 18, 19, 21, and 23 wk of age for birds from G1, at 14, 17, 19, 21, and 23 wk of age for birds from G2, and at 12, 13, 14, 16, 17 and 19 wk of age for birds from G3. For each time point, five blind and five sighted males were sacrificed. The abdominal cavity was cut open and the testes were removed and weighed to monitor testicular development. In addition, before sacrifice, other measurements that relate to maturation, such as body weight and comb length, were also taken. Histology As the largest and most significant anatomical differences were observed between blind and sighted animals left non-photostimulated, histology was performed on testes collected from G2 birds at 14, 17 and 19 wk of age. Tissues were fixed in formalin, dehydrated through baths of progressively more concentrated ethanol, treated with xylene, and then embedded into paraffin. The tissue blocks were sectioned at 4 to 5 mm, and slices were placed on microscope slides. Sections were then deparaffinized and stained with hematoxylin and eosin (H&E stain). Slides were scanned by a digital scanner and analyzed by the Image Scope Analytical computer software (Aperio Technologies, Vista, CA). Seminiferous tubules and lumen epithelium depth and diameter were measured, and stages of spermatogenesis were determined. Image Scope allowed multiple measurements to be taken on one slide and, a random selection of 100 seminiferous tubules were analyzed from each individual (five blind and five sighted) for each time point. Horizontal and vertical diameter of the seminiferous tubule and lumen were taken and the average measurement was used for calculation. The presence of Sertoli cells, spermatogonia, primary spermatocytes, spermatids and spermatozoa in the seminiferous tubule was recorded. Similarly, the presence of Leydig cells in the interstitial tissue between seminiferous tubules was determined. Blood Collection and Hormone Assay Around expected sexual maturation, blood samples were collected from birds to be sacrificed (five blind five sighted). Blood was drawn from the brachial vein and plasma samples were stored at 208C until assayed. Levels of testosterone were measured in plasma using a commercial ELISA (Neogen, Lansing, MI) and preparation of reagents and extraction was performed according to the manufacturer s procedure with some modifications. Samples (100 ml plasma) were first extracted with

3 PERTTULA AND BE DE CARRATS * ADVANCED SEXUAL MATURATION IN BLIND ROOSTERS ml of ethyl ether in a glass tube, and, after solvent was evaporated in the organic phase, residues were dissolved in 100 ml of assay buffer. Samples were further diluted (5-, 10- or 15-fold) depending on the age of the bird so that levels would fit within the assay range of the standard curve (from 0 to 0.2 ng ml 1 ). The assay was then performed according to the manufacturer s instructions and testosterone levels were obtained by plotting the standard curve using non-linear regression equation from GraphPad Prism 4 software (GraphPad Software, La Jolla, CA). Statistical Analysis All statistical analyses were performed using GraphPad Prism 4 analysis software (GraphPad Software, La Jolla, CA). The effects and possible interactions of age and sight (blind versus sighted) were analyzed for each parameter by a two-way analysis of variance (ANOVA) (results are presented in Table 1). Whenever significant differences were detected, pairwise comparisons were performed using Bonferroni post-hoc test. Table 1. Results of the two-way ANOVA z RESULTS Changes in Body Weight and Comb Length Changes in body weight are presented in Fig. 1. No significant increase in body weight was observed between 14 and 23 wk of age for G1 birds (Fig. 1A). Similarly, no significant difference in body weight was observed between blind and sighted animals at each time point examined for this generation (Fig. 1A). However, when left un-stimulated (G2), body weight was significantly impacted by the age (P B0.0001, Table 1) as sighted roosters significantly gained weight between 14 and 19 wk of age (P B0.01), while blind males increased their body weight significantly at 21 wk of age (P B0.001) (Fig. 1B). Although sight did not have a significant effect on its own (P 0.27), a significant interaction (P 0.02) between age and sight on body weight gain was observed for this generation (Table 1), and sighted animals were significantly heavier than their blind counterpart at 19 wk of age (P B0.01). When cockerels were photostimulated at 12 wk of age (G3), both age (PB0.0001) and sight (P0.002) had an effect on body weight changes (Table 1) as all birds (blind and sighted) progressively gained weight until they reached 16 wk of age and sighted animals were significantly heavier than blinds at 14 (PB0.05) and 16 (PB0.05) wk of age (Fig. 1C). However, no significant interaction between the two factors was detected (P 0.89). No difference in comb length was observed between blind and sighted birds for any of the three generations. However, although no significant interaction between age and sight was detected, the age had consistently a significant (P B0.001) effect (Table 1 and Fig. 2). For G1 and G2 birds, combs from blind cockerels significantly increased in length between 14 and 17 wk of age (P B0.001), while comb growth for sighted birds was more gradual and delayed, reaching significance at 18, 19 wk of age for G1 (PB0.001) and G2 (PB0.01), respectively (Fig. 2A, 2B). When birds were photostimulated at 12 wk of age (G3), combs from sighted and blind birds significantly grew from 12 to 16 wk of age Sight effect Age effect Interaction Effect of sight (blind versus sighted) and age on changes in body weight G1 F3.54; df1; P0.07 F1.93; df5; P0.11 F0.83; df5; P0.54 G2 F1.24; df1; P0.27 F11.69; df4; PB F3.35; df4; P0.02 G3 F11.50; df1; P0.002 F47.34; df5; PB F0.32; df5; P0.89 Effect of sight (blind versus sighted) and age on changes in comb length G1 F1.29; df1; P0.14 F29.85; df5; PB F2.26; df5; P0.06 G2 F0.06; df1; P0.80 F27.57; df4; PB F1.54; df4; P0.21 G3 F3.03; df1; P0.09 F51.33; df5; PB F1.61; df5; P0.18 Effect of sight (blind versus sighted) and age on changes in relative testes weight G1 F1.02; df1; P0.32 F48.90; df5; PB F0.43; df5; P0.82 G2 F0.97; df1; P0.33 F154.60; df4; PB F10.32; df4; PB G3 F0.76; df1; P0.39 F47.14; df5; PB F0.47; df5; P0.78 Effect of sight (blind versus sighted) and age on changes in testosterone levels G1 F0.77; df1; P0.38 F7.55; df5; PB F0.27; df5; P0.93 G2 F0.66; df1; P0.42 F50.85; df4; PB F0.88; df4; P0.48 G3 F0.36; df1; P0.55 F6.96; df5; PB F0.31; df5; P0.91 Effect of sight (blind versus sighted) and age on changes in seminiferous tubule diameter G2 F477; df1; PB F56090; df2; PB F366; df2; PB Effect of sight (blind versus sighted) and age on changes in seminiferous tubule lumen G2 F5.9; df1; P0.023 F48.92; df2; PB F7.048; df2; P0.004 z G, generation; F, ratio of mean square value to the residual mean square; df, degrees of freedom. Cells in bold characters correspond to significant effects or interactions.

4 486 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 1. Changes in body weight. (A) Generation 1 (G1) photostimulated at 17 wk of age. (B) Generation 2 (G2) left un-photostimulated. (C) Generation 3 (G3) photostimulated at 12 wk of age. Results are expressed as mean9sem body weight (kg). Significant differences between blind and sighted birds are displayed by an asterisk (*) (PB0.05). Bars with different superscript letters ( a, b ) indicate significant differences between blind animals over time, while bars with different superscript numbers ( 1, 2 ) indicate significant differences between sighted animals overtime. (Fig. 2C). However, further significant growth was observed for blind animals between 17 and 19 wk of age (P B0.05). Testicular Growth All testicular weights were expressed as a percent of body weight to account for any variation in body size between birds. As for comb length, the age had a significant effect for all three generations, and while sight status did not independently impact testicular growth a significant interaction between the two factors Fig. 2. Changes in comb length. (A) Generation 1 (G1) photostimulated at 17 wk of age. (B) Generation 2 (G2) left un-photostimulated. (C) Generation 3 (G3) photostimulated at 12 wk of age. Results are expressed as mean9sem comb length (mm). Significant differences between blind and sighted birds are displayed by an asterisk (*) (PB0.05). Bars with different superscript letters ( a, b ) indicate significant differences between blind animals over time, while bars with different superscript numbers ( 1, 2 ) indicate significant differences between sighted animals overtime. was observed for G2 (PB0.0001) only (Table 1). For G1 birds, the relative weight of testes from blind birds increased significantly between 14 and 17 and between 18 and 21 wk of age (PB0.05). In sighted males, the first significant increase in testicular weight was observed at 19 wk of age (P B0.001) (2 wk post-photostimulation), and continued increasing until 21 wk (P B0.05; Fig. 3A). Thus, as for comb growth, blind roosters showed evidence of premature testicular growth, before photostimulation. When left non-photostimulated (G2), the difference in testicular weight was even more pronounced (Fig. 3B) and testes from blind roosters

5 PERTTULA AND BE DE CARRATS * ADVANCED SEXUAL MATURATION IN BLIND ROOSTERS 487 were significantly larger than those from sighted animals at 19 wk (PB0.001). However, similarly to what was observed when stimulated at 17 wk (G1), testes from blind males significantly increased in size between 14 and 17 wk of age (PB0.05). Conversely, testes from sighted roosters did not show significant testicular growth before 19 wk of age (PB0.05), but did continue to grow until 23 wk to become significantly heavier than those of blind animals (P B0.001) (Fig. 3B). Interestingly, although a direct statistical comparison cannot be performed between generations, at 19 wk of age the average relative testicular weight of sighted males from G2 (0.17%) was half that of G1 (0.39%), while it was not the case for blind animals (0.41% for G2 vs. 0.33% for G1). This confirms the observation that testes in blind birds increase between 14 and 19 wk of age independently of photostimulation. When photostimulated at 12 wk of age (G3), testes from sighted and blind cockerels developed in a similar manner, with both group displaying a significant increase starting between 14 and 16 wk of age (Fig. 3C). A representative picture of testes collected from blind and sighted roosters for each generation is shown on the right hand side of Fig. 3. Plasma Testosterone No significant effect of sight on testosterone levels was observed for any of the generations (Table 1). However, as for comb length and testicular weight, the age of animals had a significant effect (P B0.0001, Table 1). When comparing circulating testosterone over time for G1, levels did increase for both blind and sighted roosters between 17 and 18 wk of age; however, significant differences with initial levels were observed only by 19 wk of age for sighted (PB0.01) and 21 wk of age for blinds (P B0.05) (Fig. 4A). When left unphotostimulated (G2), plasma testosterone levels significantly increased from initial levels for both blind and sighted animals at 21 wk of age (Fig. 4B). Interestingly, testosterone levels for both blind and sighted birds remained low (below 0.5 ng ml 1 ) until 21 wk for G2, while they increased to over 1.2 ng ml 1 1 wk after photo-stimulation (18 wk of age) in G1 birds. Conversely, although levels of testosterone tended to increase earlier in sighted (between 12 and 14 wk of age) than blind animals (between 14 and 16 wk of age) for G3 (Fig. 4C), no significant differences were observed before 16 wk of age for both groups (4 wk postphotostimulation). Histology of Testes from Roosters Left un- Photostimulated (G2) Representative histology slides are presented in Fig. 5. Age and sight had both a significant effect on seminiferous tubules diameter and tubular lumen (Table 1). Furthermore, the interactions between these two factors were also highly significant (Table 1). At 14 wk of age, the average tubule diameter was not different between blind and sighted roosters ( mm, mm; P 0.85, respectively) and although tubular lumen was wider in blind birds ( mm versus mm) the difference was not significant. Nonetheless, the amount of tubules that had started to develop a lumen was higher in blind (65%) than sighted (25%) birds. At 17 wk of age, significant (PB0.01) difference in the diameter of tubules was observed between blind and sighted animals ( mm blind, mm sighted). However, although still not significant, the lumen of the tubules tended to be larger in testes from blind than from sighted roosters ( mm, mm; P 0.19, respectively). At this stage, spermatogenic epithelium from both blind and sighted birds contained Sertoli cells, spermatogonia and primary spermatocytes. At 19 wk of age, tubules in testes from blind roosters were significantly larger than those from sighted animals ( blind, mm sighted, P B 0.001). The lumen was also significantly wider in blind than in sighted roosters ( blind, , mm, P B0.001). At that age, spermatogonia, spermatocytes, and spermatids were present in the tubules from both blind and sighted roosters, indicating initiation of spermatogenesis for both. However, 90% of the tubules in testes from blind roosters had spermatozoa in the lumen while only 4% of the tubules for sighted birds had all stages of spermatogenesis. DISCUSSION When photostimulated at 17 wk of age no significant difference in body weight was observed between blind and sighted males. Similar results have previously been reported in birds blinded by enucleation (Ookawa 1970) and in Japanese quail (Sayler and Wolfson 1968), assuming birds have free access to feed. When roosters were kept non-photostimulated a significant age effect on body weight and an interaction between age and sight were observed. However, the difference between blind and sighted animals only occurred at 19 wk of age for this generation. When birds were photostimulated at 12 wk of age, sighted animals were heavier than blind ones the following weeks indicating that differences in body weight gain between blind and sighted birds could be observed when photostimulated before they reach an adult size (around 17 wk of age). A link between body weight, feed consumption and the rate of sexual maturation has previously been reported, and greatly depends on the sex and type of animal studied (broiler breeder vs. layer type chicken). For example, for female broiler breeders, photostimulation of hens before they reach a mature size decreases the number of eggs produced and increasing feed consumption during maturation increases production (Renema et al. 1999). Comb length is commonly used as a marker of sexual maturation and in our study only the age had a significant effect. However, comb length of blind males consistently increased between 14 and 17 wk of age for

6 488 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 3. Changes in testicular weight. (A) Generation 1 (G1) photostimulated at 17 wk of age. (B) Generation 2 (G2) left unphotostimulated. (C) Generation 3 (G3) photostimulated at 12 wk of age. Results are expressed as mean9sem testicular weight as percent of body weight. Significant differences between blind and sighted birds are displayed by an asterisk (*) (PB0.05). Bars with different superscript letters ( a, b ) indicate significant differences between blind animals over time, while bars with different superscript numbers ( 1, 2 ) indicate significant differences between sighted animals overtime. Pictures on the right correspond to representative photographs of testes from blind and sighted birds for each corresponding generation. G1 and G2 generations, while the growth was more gradual in sighted birds. This is not surprising, as comb growth has been shown to be under the control of androgens (Zeller 1971) and thus related to gonadal development. Although in our study we did observe a significant difference in relative testicular weight between blind and sighted roosters from G2 at 19 wk of age, the lack of significant difference in comb length may reflect the lack of differences in circulating testosterone levels. Although it has been well established that during photostimulation light penetrates the skull to directly activate hypothalamic (extra-retinal) photoreceptors (Morbakey et al. 2010), to date the contribution of the eye toward sexual maturation remains controversial. For example, in sparrows Menaker et al. (1968) found

7 PERTTULA AND BE DE CARRATS * ADVANCED SEXUAL MATURATION IN BLIND ROOSTERS 489 Fig. 4. Changes in plasma testosterone levels. (A) Generation 1 (G1) photostimulated at 17 wk of age. (B) Generation 2 (G2) left un-photostimulated. (C) Generation 3 (G3) photostimulated at 12 wk of age. Results are expressed as mean9 SEM of testosterone levels (ng ml 1 ). Significant differences between blind and sighted birds are displayed by an asterisk (*) (PB0.05). Bars with different superscript letters ( a, b ) indicate significant differences between blind animals over time, while bars with different superscript numbers ( 1, 2 ) indicate significant differences between sighted animals overtime. that testicular development is normal with or without the eye. On the other hand, the rate of sexual maturation was accelerated in blinded male quail (Siopes and Wilson 1974). In our experiment, the size of testes from blind roosters increased significantly between 14 and 17 wk of age (before photostimulation). This early spontaneous maturation was further evident when birds were left non-photostimulated as blind roosters also matured at around 17 wk of age with significantly heavier testes than sighted birds at 19 wk of age. However, since photostimulation at 12 wk of age did trigger sexual maturation in both our blind and sighted birds, we can conclude that blind animals are still photosensitive despite the early spontaneous maturation observed in animals left unstimulated (G2). In addition to testis size, major differences were observed at the tissue level, and blind roosters demonstrated earlier spermatogenic development than sighted. Gonza lez- Mora n et al. (2008) previously showed that histological features and sex hormone receptors change during the different life stages of chickens. Although Sertoli cells are primarily controlled by FSH and Leydig cells by LH, FSH can increase the response to LH by increasing the number of LH receptors expressed on cells. When stimulated by LH, Leydig cells will then produce testosterone, which is required by the Sertoli cells for spermatogenesis. At 14 wk of age, both blind and sighted birds displayed tubules with simple layers of spermatogonia and Sertoli cells surrounded by a basal lamina, and a high proportion of Leydig cells in the interstitial tissue. However, at a later stage, 90% of the tubules in testes from blind roosters had spermatozoa in the lumen, while for sighted birds only 4% of the tubules had complete spermatogenesis. It is interesting to note that the earlier development observed in blind roosters occurred with no sign of higher testosterone thus LH increase. This could suggest an influence by FSH, which supports the function of Sertoli cells, which in turn supports many aspects of sperm cell maturation. One alternative explanation for the observed differences between blind and sighted roosters may be that instead of blind animals displaying advanced sexual maturation, sighted animals display a delayed activation of the reproductive axis. Recently, the existence of an inhibitory pathway involving GnIH has been reported in several species (for review: Tsutsui et al. 2010) and in birds, melatonin produced by the retina of the eye and the pineal gland does stimulate the hypothalamic production of GnIH during dark phases (Ubuka et al. 2005; Chowdhury et al. 2010). Thus, the lack of a functional retina in Smoky Joe rooster may result in altered melatonin levels, thus partly lifting or minimizing the inhibitory input. Furthermore, as the presence of both GnIH and its receptor has also been reported throughout the testis structures in several bird species (Bentley et al. 2008), it is also possible that the difference observed on testicular growth and spermatogenesis occurs locally within the gonads. However, although melatonin levels

8 490 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 5. Representative histology slides of testes from roosters left un-photostimulated (G2). (A) Testis from a blind bird at 14 wk of age. (B) Testis from a sighted bird at 14 wk of age. (C) Testis from a blind bird at 17 wk of age. (D) Testis from a sighted bird at 17 wk of Age. (E) Testis from a blind bird at 19 wk of age. (F) Testis from a sighted bird at 19 wk of age. All images correspond to a 40magnification. in the retina and serum of another genetically blind line of chicken (rc/rc, characterized by the degeneration of photoreceptors in the retina) were shown to be significantly lower than those of unaffected control birds (Pang et al. 1989), the impact of blindness on melatonin and the GnIH system in our birds remains to be confirmed and this hypothesis needs to be verified. In conclusion, we report here that the lack of a functional retina in blind Smoky Joe roosters results in earlier sexual maturation compared with their sighted counterparts and this maturation appears to happen spontaneously at around 18 wk of age when not photostimulated. ACKNOWLEDGMENTS This work was supported in part by the Poultry Industry Council, the Natural Sciences and Engineering Research Council of Canada and the Ontario Ministry of Agriculture, Food and Rural Affairs. Benoit, J The role of the eyes and the hypothalamus in the photo-stimulation of the gonads of the duck. Ann. NY Acad. Sci. 117: Bentley, G. E., Ubuka, T., McGuire, N. L., Chowdhury, V. S., Morita, Y., Yano, T., Hasunuma, I., Binns, M. and Wingfield, J. C Gonadotropin inhibitory hormone and its receptor in the avian reproductive system. Gen. Comp. Endocrinol. 156: Chowdhury, V. S., Yamamoto, K., Ubuka, T., Bentley, G. E., Hattori, A. and Tsutsui, K Melatonin stimulates the release of gonadotropin-inhibitory hormone by the avian hypothalamus. Endocrinology 151: Dawson, A., King, V. M., Bentley, G. E. and Ball, G. F Photoperiodic control of seasonality in birds. J. Biol. Rhythms 16:

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