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Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens a
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A.L. Geng , S.F. Xu , Y. Zhang , J. Zhang , Q. Chu & H.G. Liu a
Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, P. R. China Accepted author version posted online: 10 Jan 2014.Published online: 22 Apr 2014.
To cite this article: A.L. Geng, S.F. Xu, Y. Zhang, J. Zhang, Q. Chu & H.G. Liu (2014) Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens, British Poultry Science, 55:2, 264-269, DOI: 10.1080/00071668.2013.878782 To link to this article: http://dx.doi.org/10.1080/00071668.2013.878782
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British Poultry Science, 2014 Vol. 55, No. 2, 264–269, http://dx.doi.org/10.1080/00071668.2013.878782
Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens A.L. GENG, S.F. XU, Y. ZHANG, J. ZHANG, Q. CHU,
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H.G. LIU
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Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, P. R. China
Abstract 1. The effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens were investigated. A total of 648, 18-week-old native laying hens (Beijing You Chicken, BYC) were randomly allocated to 6 groups with 3 replicates. The birds were exposed to 1 of 6 different photoperiods, including 16L:8D (06:00 to 22:00 h) for group 1; 12L:2D:4L:6D for group 2; 8L:4D:4L:8D for group 3; 16L:8D (03:00 to 19:00 h) for group 4; 14L:10D for group 5; and 18L:6D for group 6. 2. The broodiness rate and egg-laying rate for weeks 20–26, 27–33, 34–40, 41–47, 48–54 and 55–61 were calculated, and serum prolactin (PRL), luteinising hormone (LH), 17-beta-oestradiol (E2), melatonin (Mel) and progesterone (P4) concentrations were measured at the end of each stage. 3. Significant effects were observed on the rate of broodiness by the photoperiod and stage, but the interaction of photoperiod and stage was not significant. The rate of broodiness for group 3 (5.9%) was significantly higher than other groups, with group 2 being the lowest (2.8%). Broodiness rate was the highest for weeks 41–47 (9.9%). Significant effects were observed on average egg-laying rate by photoperiod and stage: the rate of egg-laying of groups 2 and 5 were significantly higher than groups 1, 4 and 6. 4. There were no significant effects of photoperiod on PRL, LH and Mel concentrations at 26, 33, 40 and 54 weeks of age (P > 0.05), but at 47 weeks of age, PRL and LH concentrations of group 1 were significantly lower than those in other groups. 5. The study suggests that the photoperiod of group 2 (12L:2D:4L:6D) is optimal for the birds’ performance to give the lowest broodiness rate and the highest egg-laying rate during the whole laying period, and 41–47 weeks may be a key stage for the photomodulation of broodiness.
INTRODUCTION Light, as one of the most important environmental factors, plays an important role in seasonal modulation of egg-laying and reproduction in birds in temperate regions (Phillips, 1992; Olanrewaju et al., 2006). Light modulates the reproductive activities through a series of signal transduction and endocrine pathways (Etches, 1996). Light also modulates the release of gonadotropin-releasing hormone and secretion of vasoactive intestinal peptide, both of which can control the seasonal changes of animals’ reproduction by promoting the secretion of prolactin
(PRL), luteinising hormone (LH) and other neuropeptides (Jacquet, 1997). Broodiness is observed in most avian species; it involves a hen sitting on her eggs for the purpose of hatching embryos, consisting of persistent nesting, turning and retrieval of eggs, characteristic clucking and defence of the nest (Romanov et al., 2002; Jiang et al., 2010). Broodiness is related to PRL concentration in some birds (Lea et al., 1981; Siopes and Burke, 1984; Sharp, 1989, 1997; March et al., 1994; Edens, 2011). The effects of photoperiod on birds are mainly reflected in its promotion of PRL secretion (Sharp, 1989) and PRL concentration (Johnston, 2004).
Correspondence to: A.L. Geng, Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, P. R. China. E-mail: [email protected] Accepted for publication 15 October 2013.
© 2014 British Poultry Science Ltd
PHOTOPERIOD ON BROODINESS AND EGG-LAYING
Beijing You Chicken (BYC) is a long-day breeding bird native to Beijing, China, which was listed as one of the most important national breeds in 2005 by the Ministry of Agriculture of the People’s Republic of China. It can lay on short days, but at a low egg-laying rate. Liu (2008) reported that BYC had broody behaviour and the broodiness was related to its low egg output. The purpose of this study was to investigate whether there was a relationship between broodiness and egg-laying of BYC and some endocrine responses under artificial photoperiods in order to provide information for the improvement of native birds’ reproduction through photomodulation.
MATERIALS AND METHODS
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Experimental design and birds The experiment was conducted at the BYC Breeding Farm, Daxing, Beijing. A total of 648, 18-week-old commercial BYC laying hens having the same genetic origin were randomly allocated to 6 groups. Each group had three replicates with 36 birds per replicate kept in a free-range like system, in which the birds were housed in separate floor pens, with access to an outdoor area. The indoor density was 7 birds per m2, and outdoor density was 2 birds per m2. Nest boxes, perches and litter were offered in each pen. The birds were housed in individually lit pens and exposed to 1 of 6 different photoperiods: 16L:8D (6:00–22:00) for group 1; 12L:2D:4L:6D (6:00–18:00, 20:00–24:00) for group 2; 8L:4D:4L:8D (6:00–14:00,18:00–22:00) for group 3; 16L:8D (3:00–19:00) for group 4; 14L:10D (6:00–20:00) for group 5; and 18L:6D (6:00–24:00) for group 6. The long photoperiod was natural illumination during the daytime plus supplementary light at night. The short photoperiod was achieved by confining the birds to their pens during the day. In order to keep the same ranging time for the birds, the groups adopted the following arrangement: lights at 6:00 in the morning everyday (except for group 4, at 3:00), birds fed 6:00–8:00, birds ranged freely 8:00–14:00 and returned to their pens at 14:00 when the second feeding time began. Special light-proof cloth and light controller were used in each pen. The birds were fed a commercial maize soyabean-based diet with 155 g CP/kg, 11.28 MJ/kg ME and 20g Ca/kg during weeks 18–20, and with 155 g CP/kg, 11.08 MJ/kg ME and 30 g Ca/kg during weeks 22–62. Incandescent lamps were used, and the bulbs were 2 m above the ground, with an average light intensity of 15 lx. Conventional temperature and humidity were given, and in severe weather conditions such as
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rain and thunder, the birds were confined inside the pen to reduce stress. The study was performed in accordance with the local ethical guidelines. Observations Video cameras were used that were combined with daily visits and observations. The broodiness rate and egg-laying rate for weeks 20–26, 27–33, 34–40, 41–47, 48–54 and 55–61 were recorded. Assessment for broodiness was by persistent nesting for more than three consecutive days, exhibiting nest defence and characteristic clucking (Jiang et al., 2010). Broodiness rate was defined as the number of hens with broodiness divided by the total number of hens during a particular stage of the laying period. Six birds not showing signs of broodiness in each replicate were chosen at the end of each stage and 3 ml blood was collected in the morning by venepuncture, centrifuged at 3000 × g on the day of collection and serum stored at –20°C until analysis. Serum PRL, LH, 17-beta-oestradiol (E2), melatonin (Mel) and progesterone (P4) concentrations were determined at the end of each stage, respectively, and the samples were all assayed in duplicate. Serum PRL concentration was quantified according to Huang et al. (2008) with a little modification. Assay sensitivity was 0.36 ng/ml in one tube of 400 µl reaction volume containing 50 µl of serum sample, and the intra-assay and inter-assay coefficients of variation on serum pools were below 15%. LH concentration was performed using RIA according to Krishnan et al. (1994). Assay sensitivity was 0.03 ng/ml in one tube of 400 µl reaction volume containing 100 µl of serum sample, and the intra-assay and inter-assay coefficients of variation on serum pools were below 15%. E2, P4 and Mel concentrations were measured using the medical diagnosis RIA kit purchased from Beijing Northern Biotechnology Institute (Beijing, China). The assay sensitivity was 0.2 pg/ml and intra-assay coefficient of variation was below 15% for E2; the assay sensitivity was 0.3 ng/ml and intra-assay coefficient of variation was below 15% for both P4 and Mel. Statistical analyses The data were analysed statistically using SPSS 15.0 software for Windows (SPSS Inc. Chicago, IL). The general linear model (GLM) was used to analyse the main effects and interaction between photoperiod and egg-laying stage. One-way analysis of variance (ANOVA) was used to analyse the effects of photoperiod on endocrine hormones. Duncan’s test was used for multiple comparisons. The percentage was arcsine transferred before analysis.
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The relationships between hormone secretion and the broodiness rate and egg-laying rate was assessed with Pearson’s correlation coefficient. Correlation coefficients of r = 0.70 or higher were regarded as having a strong positive correlation, and when r = 0.30 to 0.70 the variables were regarded as having a moderate positive relationship. P < 0.05 was regarded as statistically significant.
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RESULTS There were no significant effects for the interaction of photoperiod and stage for the broodiness rate (P = 0.223) and egg-laying rate (P < 0.165), and the marginal effects of photoperiod on the broodiness rate and egg-laying rate are shown in Table 1. (Group × stage means are presented in the Supplementary Table available via the online version of the article at http://dx.doi.org/ 10.1080/00071668.2013.878782). Significant effects were observed on average broodiness rate by photoperiod and stage alone (P = 0.002 and P = 0.001). The broodiness rate for group 3 (5.9%) was significantly higher than those of other groups (P < 0.05), with group 2 being the lowest (2.8%, P < 0.05). For different stages, the broodiness rate was highest (9.9%) for 41–47 weeks, next highest for 34–40 weeks (5.4%), lower for 48–54 weeks (3.1%) and 27–33 weeks (2.8%), and lowest for 55–61 (0.9%) and 20–26 weeks (0.5%) (P < 0.05), indicating that there was a higher broodiness rate for the middle stage (34– 47 weeks) and lower broodiness rate for the early and late stages (before 34 weeks and after 48 weeks). Significant effects were observed on the average egg-laying rate by stage (P = 0.001), and photoperiod was almost statistically significant (P = 0.054). The egg-laying rates of groups 2 (62.9%) and 5 (61.7%) were significantly higher than those of groups 1, 4 and 6 (P < 0.05), but group 3 (61.1%) showed no significant difference from the other groups (P > 0.05). The egg-laying rate for different stages differed: 27–33 weeks (74.8%) and 34–40 weeks (70.0%) were significantly higher than those for the other 4 stages (P < 0.05), and no significant differences were shown among the other 4 stages (P > 0.05). Serum PRL concentration was 87–138 ng/ml for 26–40 weeks (see Figure 1(a)), began to increase at 41 weeks and increased substantially to 163–225 ng/ml at 47 weeks. There was no significant effect of photoperiod on PRL concentration at 26, 33, 54 and 61 weeks of age (P > 0.05). The PRL concentration of group 3 was significantly higher than those in other groups (P < 0.05). At 47 weeks, PRL concentrations of groups 3 and 4 were significantly higher than those in groups 1, 5 and 6 (P < 0.05).
Serum LH concentration was 6.74–9.76 ng/ ml for 26–40 weeks (Figure 1(b)) and gradually decreased to 41 weeks. There were no significant effects of photoperiod on LH concentration at 26, 33, 40 and 54 weeks (P > 0.05). The LH concentration of group 3 was significantly lower than those in the other 5 groups at 47 weeks (P < 0.05). Figure 1(c) shows that the serum E2 concentration was 34–58 pg/ml for 26–40 weeks, increased at 41 weeks, reached more than 100 pg/ml during weeks 47–54 before decreasing after 61 weeks. There were significant effects of photoperiod on E2 concentration (P < 0.05). The E2 concentrations of groups 1 and 3 were significantly lower than those in groups 5 and 6 (P < 0.05) at 33 weeks of age. The E2 concentrations of groups 3 and 4 were significantly higher than those in groups 5 and 6 (P < 0.05) at 40 weeks of age. At 47 weeks of age, the E2 concentration of groups 1 and 5 were significantly higher than those in groups 2, 3, 4 and 6 (P < 0.05). Figure 1(d) shows that serum Mel concentration did not change at different egg-laying stages (P > 0.05). The Mel concentration of group 1 was significantly higher than that of groups 2, 3 and 5 (P < 0.05), but lower than that of group 6 (P < 0.05) at 47 weeks of age. Figure 2 shows that serum P4 concentration was unchanged at different egg-laying stages. The P4 concentrations of groups 1 and 3 were significantly higher than in groups 5 and 6 at 33 weeks of age (P < 0.05), and the P4 concentration of group 1 was significantly higher than in group 2 at 40 weeks (P < 0.05). At 47 weeks of age, the P4 concentration of group 1 was significantly higher than in groups 3, 5 and 6 (P < 0.05) and lower than in groups 2 and 4 (P < 0.05). Correlations between traits are presented in Table 2, which shows that there was a strong positive relationship between broodiness rate and PRL concentration (r > 0.70), but for broodiness rate and other hormones, there was no strong positive relationship (r < 0.70). The correlation coefficient between broodiness rate and hormone concentrations was influenced by photoperiod, especially for rE2 and rP4 (P < 0.05). Group 1’s rE2 was significantly higher than for other groups (P < 0.05), and rP4 for group 5 was significantly higher compared with the other groups (P < 0.05). The correlation coefficient between egg-laying rate and hormone concentrations was not influenced by photoperiod, as shown in Table 3.
DISCUSSION Broodiness is one of the maternal expressions of female birds. Different breeds have a different prevalence of broodiness such as 30–50% for turkeys (Gueméné and Williams, 1994; Leighton
PHOTOPERIOD ON BROODINESS AND EGG-LAYING
20–26
27–33
34–40
41–47
48–54
55–61
GLM analysis Photoperiod
P-value Stage (weeks)
P-value Photoperiod × stage P-value
1 2 3 4 5 6 20–26 27–33 34–40 41–47 48–54 55–61
54.2fgh 59.0bcdefgh 52.0gh 48.4h 53.0fgh 52.6fgh 74.4ab 76.8a 77.5a 73.5ab 76.9a 70.6abcd 71.9ab 70.9abcd 71.3abc 68.6abcdef 70.2abcde 67.3abcdefg 53.8fgh 57.7c 55.8c 54.0fgh 59.3bcdefg 52.9c 49.8h 56.9c 55.3defgh 47.0h 57.4c 48.6h 47.4h 56.4c 54.5efgh 50.1h 54.2fgh 54.7efgh 0.94
Arcsine transformation 3.1b 2.8b 5.9a 4.2b 3.7b 3.1b 0.002 0.5d 2.8c 5.4b 9.9a 3.1c 0.9d 0.001 0.223
58.4b 62.9a 61.1ab 54.9b 61.7a 57.9b 0.054 53.2b 74.8a 70.0a 55.6b 52.5b 52.9b 0.001 0.165
Photoperiodic treatments: 1, 16L:8D (0600 to 2200 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (0300 to 1900 h); 5, 14L:10D; 6, 18L:6D. a,b,c Within a column, values not sharing a common superscript letter are significantly different (P < 0.05).
et al., 2001), 78% for bantam hens (Romanov et al., 2002), 17–18% for Muscovy duck (Lin,
Prolactin, ng/ml
0.9hi 0i 0i 0i 0.9hi 0.9hi 1.9ghi 1.9ghi 4.6defgh 2.8fghi 3.7efghi 1.9ghi 3.7efghi 4.6defgh 8.3bcd 6.5def 5.6efg 3.7efghi 8.3bcd 7.4ce 14.8a 11.1b 10.2bc 7.4ce 2.8fghi 1.9ghi 5.6d 3.7efhi 1.9ghi 2.8fhi 0.9hi 0.9hi 1.9ghi 0.9hi 0i 0.9hi 0.37
2
3
4
5
6
230 200 170 140 110 80 50 20 26
33
40 47 Age, weeks
b 1 Luteinising hormone, ng/ml
1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 SEM
Broodiness rate (%)
Egglaying rate (%)
2
3
4
54
61
5
6
10 8 6 4 2
26
33
40
47
54
61
Age, weeks
c 1
2
3
4
5
6
230 Oestradiol, pg/ml
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Photoperiodic treatments
Egglaying stage (weeks)
1
a
180 130 80 30
26
33
40 47 Age, weeks
1
d Melatonin, ng/ml
Effects of photoperiod and stage on broodiness rate and egg-laying rate of Beijing You laying hens
2
3
54
4
61
5
6
360 330 300 270 240 210 180 150 120 90 26
33
40 47 Age, weeks
54
61
Figure 1. Average serum concentrations of PRL (a), LH (b), 17-beta-oestradiol (E2) (c) and Mel (d) in laying hens under different photoperiodic treatments: 1, 16L:8D (0600 to 2200 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (0300 to 1900 h); 5, 14L:10D; 6, 18L:6D.
2005) and 15% for Qingyuan chickens (Jiang et al., 2010). Different egg-laying stages also affect the incidence of broodiness. Guemene and 1 Progesterone, ng/ml
Table 1.
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2
3
4
5
6
80 60 40 20 0
26
33
40 47 Age, weeks
54
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Figure 2. Average P4 concentration in laying hens under different photoperiodic treatments: 1, 16L:8D (0600 to 2200 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (0300 to 1900 h); 5, 14L:10D; 6, 18L:6D.
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Table 2. Groups 1 2 3 4 5 6 P-value
Effects of photoperiod on correlation coefficients between broodiness rate and endocrine hormones Photoperiodic treatments
16L:8D (6:00–22:00) 12L:2D:4L:6D (6:00–18:00, 20:00–24:00) 8L:4D:4L:8D (6:00–14:00, 18:00–22:00) 16L:8D (3:00–19:00) 14L:10D (6:00–20:00) 18L:6D (6:00–24:00)
rPRL 0.85 0.81 0.82 0.82 0.92 0.76 0.055
rLH 0.12 0.16 0.01 0.28 0.24 0.09 0.061
rE2 a
0.60 0.14b 0.28b 0.32b 0.39b 0.29b 0.044
rMel
rP4
0.89 0.35 0.57 0.94 0.67 0.92 0.062
0.42b 0.35c 0.50b 0.60ab 0.74a 0.51b 0.045
Photoperiodic treatments: 1, 16L:8D (06:00 to 22:00 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (03:00 to 19:00 h); 5, 14L:10D; 6, 18L:6D. PRL, prolactin; LH, luteinising hormone; E2, 17-beta-oestradiol; Mel, melatonin; P4, progesterone. a,b.c Within a column, values not sharing a common superscript letter are significantly different (P < 0.05).
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Table 3.
Effects of photoperiod on correlation coefficients between egg-laying rate and endocrine hormones
Groups
Photoperiods
rPRL
rLH
rE2
rMel
rP4
1 2 3 4 5 6 P-value
16L:8D (6:00–22:00) 12L:2D:4L:6D(6:00–18:00, 20:00–24:00) 8L:4D:4L:8D (6:00–14:00, 18:00–22:00) 16L:8D (3:00–19:00) 14L:10D (6:00–20:00) 18L:6D (6:00–24:00)
0.29 0.39 0.15 0.18 0.42 0.26 0.062
0.77 0.86 0.81 0.65 0.71 0.85 0.058
−0.51 −0.70 −0.69 −0.53 −0.43 −0.70 0.072
0.38 0.66 0.65 0.17 0.77 0.01 0.075
0.83 0.89 0.71 0.67 0.69 0.54 0.057
Photoperiodic treatments: 1, 16L:8D (06:00 to 22:00 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (03:00 to 19:00 h); 5, 14L:10D; 6, 18L:6D. PRL, prolactin; LH, luteinising hormone; E2, 17-beta-oestradiol; Mel, melatonin; P4, progesterone.
Williams (1994) studied the broodiness index and plasma concentrations of PRL, LH, oestradiol and P4 throughout the first period of laying in turkey hens, and found that there was a significant effect of laying stage. The present study indicated that the average broodiness rate of BYC was 5.9% during the complete egg-laying stage (20–62 weeks), and there were different broodiness rates at different egg-laying stages. With the rapid increase of egg-laying during 27–33 weeks and 34–40 weeks, the broodiness rate also increased and the highest broodiness rate (9.9%) occurred during 41–47 weeks. The effect of photoperiod on birds is mainly reflected in its regulation of PRL concentration (Johnston, 2004). As a key mediator of seasonal breeding, PRL plays an important role in neuroendocrine regulation (Sharp and Blache, 2003). Proudman (1998) observed that the turkey’s PRL concentration was higher under a long photoperiod compared with a short photoperiod. In this study, photoperiodic group 2 showed the lowest rate of broodiness (2.8%) and the highest egg-laying rate (62.9%), which suggests that the photoperiod 12L:2D:4L:6D is optimal for the birds’ performance. The reason for this result may be due to optimal PRL and LH concentrations mediated by the photoresponsiveness of the birds. Photoperiodic group 3 had the highest rate of broodiness (5.9%), but its egg-laying rate (61.1%) was not significantly different from the other groups, which suggests that the higher broodiness rate was partially compensated for by a
greater rate of egg-laying in the non-broody periods or by non-broody hens (Jiang et al., 2010). Burke and Dennison (1980) reported that the PRL concentration was low (22 ng/ml) before the lighting stimulus and gradually increased to 45– 50 ng/ml at first egg, reaching 100 ng/ml or more in the initial egg-laying stages. There was a circadian rhythm for bantam hen PRL secretion, and PRL concentration was lower during the day than at night under a long photoperiod (Lea et al., 1981; Curlewis, 1992). Huang et al. (2008) reported that plasma PRL concentration of Magang geese was low in the breeding season (approximately 10 ng/ml) and rose to higher concentration (between 20 and 30 ng/ml) in the non-breeding season under the long photoperiod. LH concentration was initially high (between 1 and 2 ng/ml) and then decreased to concentrations below 1 ng/ml. In this study, there were no significant effects of photoperiod on PRL, LH and Mel concentration at 26, 33, 40 and 54 weeks of age, but at 47 weeks of age, PRL and LH concentrations in group 1 were significantly lower than those in the other groups. E2 and P4 concentrations in group 1 were significantly different from those in groups 2, 3, 4 and 6. Huang et al. (2008) proposed that PRL secretion was positively correlated with photoperiod for Magang geese. The present study found that the broodiness rate and PRL concentration had a strong correlation (r > 0.70). The correlation coefficient was also influenced by the photoperiod, and further research is
PHOTOPERIOD ON BROODINESS AND EGG-LAYING
needed to discover the mechanism of this relationship. Conclusion
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The present study suggests that the photoperiodic group 2 (12L:2D:4L:6D) is optimal for laying performance, for which it gives the lowest rate of broodiness and the highest rate of egg laying during the whole laying period. This may be due to optimal PRL and LH concentrations mediated by the photoresponses of the birds. Group 3 (8L:4D:4L:8D) had the highest rate of broodiness (5.9%), but its egg-laying rate showed no significant difference compared with the other groups, which suggests that the highest broodiness rate is not always associated with the lowest rate of overall egg-laying. The present study also suggests that 41–47 weeks may be a key stage for the photomodulation of broodiness.
ACKNOWLEDGEMENTS The authors wish to thank the National Natural Science Funds [grant number 30972128] and Beijing Natural Science Funds [grant number 6102010] for providing financial supports, Mr Liu Zhengkang for animal keeping and Ms Xiaolin Shi for some detailed observations on site.
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JACQUET, J.M. (1997) Photorefractory period of the Muscovy duck (Cairina moschata): endocrine and neuroendocrine responses to day length after a full reproductive cycle. British Poultry Science, 38 (2): 209–216. JIANG, R.S., CHEN, X.Y. & GENG, Z.Y. (2010) Broodiness, egg production, and correlations between broody traits in an indigenous chicken breed. Poultry Science, 89 (6): 1094–1096. JOHNSTON, J.D. (2004) Photoperiodic regulation of prolactin secretion: changes in intra-pituitary signalling and lactotroph heterogeneity. Journal of Endocrinology, 180 (3): 351–356. KRISHNAN, K.A., PROUDMAN, J.A. & BAHR, J.M. (1994) Purification and partial characterization of isoforms of luteinizing hormone from the chicken pituitary gland. Comparative Biochemistry and Physiology, Biochemistry and Molecular Biology, 108 (6): 253–264. LEA, R.W., DODS, A.S.M., SHARP, P.J. & CHADWICK, A. (1981) The possible role of prolactin in regulation of nesting behavior and the secretion of luteinizing hormone in broody bantams. The Journal of Endocrinology, 91 (10): 89–97. LEIGHTON, A.T., LIN, Y.C. & PROUDMAN, J.A. (2001) Antibodies to curb broodiness of turkeys. World Poultry, 17 (2): 28–29. LIN, F.Z. (2005) Broody rules and change regularity of reproductive hormone and polymorphism of microsatellite on PRL gene in Muscovy ducks. Master Thesis, Fujian University of Agriculture and Forestry, Fujian (in Chinese). LIU, H.G. (2008) Studies on meat flavours and candidate genes of partial important economical traits in Beijing Fatty Chicken. PhD Dissertation, China Agricultural University, Beijing (in Chinese). MARCH, J.B., SHARP, P.J., WILSON, P.W. & SANG, H.M. (1994) Effect of active immunization against recombinant-derived chicken prolactin fusion protein on the onset of broodiness and photoinduced egg laying in bantam hens. Journal of Reproduction and Fertility, 101 (1): 227–233. OLANREWAJU, H.A., THAXTON, J.P., DOZIER, W.A., PURSWELL, J., ROUSH, W.B. & BRANTON, S.L. (2006) A review of lighting programs for broiler production. Poultry Science, 5 (4): 301–308. PHILLIPS, C.J.C. (1992) Environmental factors influencing the production and welfare of farm animals: photoperiod, in: PHILLIPS, C.J.C. & PIGGINS, D. (Eds) Farm Animals and the Environment, pp. 49–65 (Oxford, CAB International). PROUDMAN, J.A. (1998) Circulating prolactin levels at the end of the photophase and the end of the scotophase throughout the reproductive cycle of the turkey hen. Poultry Science, 77 (2): 303–308. ROMANOV, M.N., TALBOT, R.T., WILSON, P.W. & SHARP, P.J. (2002) Genetic control of incubation behavior in the domestic hen. Poultry Science, 81 (7): 928–931. SHARP, P.J. (1989) Physiology of egg production, in: HARESIGH, N.W. (Ed) Recent Advance in Turkey Science, pp. 31–54 (London, Nems Butterworths). SHARP, P.J. (1997) Immunological control of broodiness. World’s Poultry Science, 53 (l): 23–31. SHARP, P.J. & BLACHE, D. (2003) A neuroendocrine model for prolactin as the key mediator of seasonal breeding in birds under long- and short-day photoperiods. Canadian Journal of Physiological Pharmacology, 81 (4): 350–358. SIOPES, T.D. & BURKE, W.H. (1984) The effect of ovariectomy on broodiness and plasma prolactin levels in turkey hens during a photo-induced reproductive cycle. Theriogenology, 22 (10): 445–453.
British Poultry Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/cbps20
Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens a
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A.L. Geng , S.F. Xu , Y. Zhang , J. Zhang , Q. Chu & H.G. Liu a
Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, P. R. China Accepted author version posted online: 10 Jan 2014.Published online: 22 Apr 2014.
To cite this article: A.L. Geng, S.F. Xu, Y. Zhang, J. Zhang, Q. Chu & H.G. Liu (2014) Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens, British Poultry Science, 55:2, 264-269, DOI: 10.1080/00071668.2013.878782 To link to this article: http://dx.doi.org/10.1080/00071668.2013.878782
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British Poultry Science, 2014 Vol. 55, No. 2, 264–269, http://dx.doi.org/10.1080/00071668.2013.878782
Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens A.L. GENG, S.F. XU, Y. ZHANG, J. ZHANG, Q. CHU,
AND
H.G. LIU
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Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, P. R. China
Abstract 1. The effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens were investigated. A total of 648, 18-week-old native laying hens (Beijing You Chicken, BYC) were randomly allocated to 6 groups with 3 replicates. The birds were exposed to 1 of 6 different photoperiods, including 16L:8D (06:00 to 22:00 h) for group 1; 12L:2D:4L:6D for group 2; 8L:4D:4L:8D for group 3; 16L:8D (03:00 to 19:00 h) for group 4; 14L:10D for group 5; and 18L:6D for group 6. 2. The broodiness rate and egg-laying rate for weeks 20–26, 27–33, 34–40, 41–47, 48–54 and 55–61 were calculated, and serum prolactin (PRL), luteinising hormone (LH), 17-beta-oestradiol (E2), melatonin (Mel) and progesterone (P4) concentrations were measured at the end of each stage. 3. Significant effects were observed on the rate of broodiness by the photoperiod and stage, but the interaction of photoperiod and stage was not significant. The rate of broodiness for group 3 (5.9%) was significantly higher than other groups, with group 2 being the lowest (2.8%). Broodiness rate was the highest for weeks 41–47 (9.9%). Significant effects were observed on average egg-laying rate by photoperiod and stage: the rate of egg-laying of groups 2 and 5 were significantly higher than groups 1, 4 and 6. 4. There were no significant effects of photoperiod on PRL, LH and Mel concentrations at 26, 33, 40 and 54 weeks of age (P > 0.05), but at 47 weeks of age, PRL and LH concentrations of group 1 were significantly lower than those in other groups. 5. The study suggests that the photoperiod of group 2 (12L:2D:4L:6D) is optimal for the birds’ performance to give the lowest broodiness rate and the highest egg-laying rate during the whole laying period, and 41–47 weeks may be a key stage for the photomodulation of broodiness.
INTRODUCTION Light, as one of the most important environmental factors, plays an important role in seasonal modulation of egg-laying and reproduction in birds in temperate regions (Phillips, 1992; Olanrewaju et al., 2006). Light modulates the reproductive activities through a series of signal transduction and endocrine pathways (Etches, 1996). Light also modulates the release of gonadotropin-releasing hormone and secretion of vasoactive intestinal peptide, both of which can control the seasonal changes of animals’ reproduction by promoting the secretion of prolactin
(PRL), luteinising hormone (LH) and other neuropeptides (Jacquet, 1997). Broodiness is observed in most avian species; it involves a hen sitting on her eggs for the purpose of hatching embryos, consisting of persistent nesting, turning and retrieval of eggs, characteristic clucking and defence of the nest (Romanov et al., 2002; Jiang et al., 2010). Broodiness is related to PRL concentration in some birds (Lea et al., 1981; Siopes and Burke, 1984; Sharp, 1989, 1997; March et al., 1994; Edens, 2011). The effects of photoperiod on birds are mainly reflected in its promotion of PRL secretion (Sharp, 1989) and PRL concentration (Johnston, 2004).
Correspondence to: A.L. Geng, Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agricultural and Forestry Sciences, Beijing 100097, P. R. China. E-mail: [email protected] Accepted for publication 15 October 2013.
© 2014 British Poultry Science Ltd
PHOTOPERIOD ON BROODINESS AND EGG-LAYING
Beijing You Chicken (BYC) is a long-day breeding bird native to Beijing, China, which was listed as one of the most important national breeds in 2005 by the Ministry of Agriculture of the People’s Republic of China. It can lay on short days, but at a low egg-laying rate. Liu (2008) reported that BYC had broody behaviour and the broodiness was related to its low egg output. The purpose of this study was to investigate whether there was a relationship between broodiness and egg-laying of BYC and some endocrine responses under artificial photoperiods in order to provide information for the improvement of native birds’ reproduction through photomodulation.
MATERIALS AND METHODS
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Experimental design and birds The experiment was conducted at the BYC Breeding Farm, Daxing, Beijing. A total of 648, 18-week-old commercial BYC laying hens having the same genetic origin were randomly allocated to 6 groups. Each group had three replicates with 36 birds per replicate kept in a free-range like system, in which the birds were housed in separate floor pens, with access to an outdoor area. The indoor density was 7 birds per m2, and outdoor density was 2 birds per m2. Nest boxes, perches and litter were offered in each pen. The birds were housed in individually lit pens and exposed to 1 of 6 different photoperiods: 16L:8D (6:00–22:00) for group 1; 12L:2D:4L:6D (6:00–18:00, 20:00–24:00) for group 2; 8L:4D:4L:8D (6:00–14:00,18:00–22:00) for group 3; 16L:8D (3:00–19:00) for group 4; 14L:10D (6:00–20:00) for group 5; and 18L:6D (6:00–24:00) for group 6. The long photoperiod was natural illumination during the daytime plus supplementary light at night. The short photoperiod was achieved by confining the birds to their pens during the day. In order to keep the same ranging time for the birds, the groups adopted the following arrangement: lights at 6:00 in the morning everyday (except for group 4, at 3:00), birds fed 6:00–8:00, birds ranged freely 8:00–14:00 and returned to their pens at 14:00 when the second feeding time began. Special light-proof cloth and light controller were used in each pen. The birds were fed a commercial maize soyabean-based diet with 155 g CP/kg, 11.28 MJ/kg ME and 20g Ca/kg during weeks 18–20, and with 155 g CP/kg, 11.08 MJ/kg ME and 30 g Ca/kg during weeks 22–62. Incandescent lamps were used, and the bulbs were 2 m above the ground, with an average light intensity of 15 lx. Conventional temperature and humidity were given, and in severe weather conditions such as
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rain and thunder, the birds were confined inside the pen to reduce stress. The study was performed in accordance with the local ethical guidelines. Observations Video cameras were used that were combined with daily visits and observations. The broodiness rate and egg-laying rate for weeks 20–26, 27–33, 34–40, 41–47, 48–54 and 55–61 were recorded. Assessment for broodiness was by persistent nesting for more than three consecutive days, exhibiting nest defence and characteristic clucking (Jiang et al., 2010). Broodiness rate was defined as the number of hens with broodiness divided by the total number of hens during a particular stage of the laying period. Six birds not showing signs of broodiness in each replicate were chosen at the end of each stage and 3 ml blood was collected in the morning by venepuncture, centrifuged at 3000 × g on the day of collection and serum stored at –20°C until analysis. Serum PRL, LH, 17-beta-oestradiol (E2), melatonin (Mel) and progesterone (P4) concentrations were determined at the end of each stage, respectively, and the samples were all assayed in duplicate. Serum PRL concentration was quantified according to Huang et al. (2008) with a little modification. Assay sensitivity was 0.36 ng/ml in one tube of 400 µl reaction volume containing 50 µl of serum sample, and the intra-assay and inter-assay coefficients of variation on serum pools were below 15%. LH concentration was performed using RIA according to Krishnan et al. (1994). Assay sensitivity was 0.03 ng/ml in one tube of 400 µl reaction volume containing 100 µl of serum sample, and the intra-assay and inter-assay coefficients of variation on serum pools were below 15%. E2, P4 and Mel concentrations were measured using the medical diagnosis RIA kit purchased from Beijing Northern Biotechnology Institute (Beijing, China). The assay sensitivity was 0.2 pg/ml and intra-assay coefficient of variation was below 15% for E2; the assay sensitivity was 0.3 ng/ml and intra-assay coefficient of variation was below 15% for both P4 and Mel. Statistical analyses The data were analysed statistically using SPSS 15.0 software for Windows (SPSS Inc. Chicago, IL). The general linear model (GLM) was used to analyse the main effects and interaction between photoperiod and egg-laying stage. One-way analysis of variance (ANOVA) was used to analyse the effects of photoperiod on endocrine hormones. Duncan’s test was used for multiple comparisons. The percentage was arcsine transferred before analysis.
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The relationships between hormone secretion and the broodiness rate and egg-laying rate was assessed with Pearson’s correlation coefficient. Correlation coefficients of r = 0.70 or higher were regarded as having a strong positive correlation, and when r = 0.30 to 0.70 the variables were regarded as having a moderate positive relationship. P < 0.05 was regarded as statistically significant.
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RESULTS There were no significant effects for the interaction of photoperiod and stage for the broodiness rate (P = 0.223) and egg-laying rate (P < 0.165), and the marginal effects of photoperiod on the broodiness rate and egg-laying rate are shown in Table 1. (Group × stage means are presented in the Supplementary Table available via the online version of the article at http://dx.doi.org/ 10.1080/00071668.2013.878782). Significant effects were observed on average broodiness rate by photoperiod and stage alone (P = 0.002 and P = 0.001). The broodiness rate for group 3 (5.9%) was significantly higher than those of other groups (P < 0.05), with group 2 being the lowest (2.8%, P < 0.05). For different stages, the broodiness rate was highest (9.9%) for 41–47 weeks, next highest for 34–40 weeks (5.4%), lower for 48–54 weeks (3.1%) and 27–33 weeks (2.8%), and lowest for 55–61 (0.9%) and 20–26 weeks (0.5%) (P < 0.05), indicating that there was a higher broodiness rate for the middle stage (34– 47 weeks) and lower broodiness rate for the early and late stages (before 34 weeks and after 48 weeks). Significant effects were observed on the average egg-laying rate by stage (P = 0.001), and photoperiod was almost statistically significant (P = 0.054). The egg-laying rates of groups 2 (62.9%) and 5 (61.7%) were significantly higher than those of groups 1, 4 and 6 (P < 0.05), but group 3 (61.1%) showed no significant difference from the other groups (P > 0.05). The egg-laying rate for different stages differed: 27–33 weeks (74.8%) and 34–40 weeks (70.0%) were significantly higher than those for the other 4 stages (P < 0.05), and no significant differences were shown among the other 4 stages (P > 0.05). Serum PRL concentration was 87–138 ng/ml for 26–40 weeks (see Figure 1(a)), began to increase at 41 weeks and increased substantially to 163–225 ng/ml at 47 weeks. There was no significant effect of photoperiod on PRL concentration at 26, 33, 54 and 61 weeks of age (P > 0.05). The PRL concentration of group 3 was significantly higher than those in other groups (P < 0.05). At 47 weeks, PRL concentrations of groups 3 and 4 were significantly higher than those in groups 1, 5 and 6 (P < 0.05).
Serum LH concentration was 6.74–9.76 ng/ ml for 26–40 weeks (Figure 1(b)) and gradually decreased to 41 weeks. There were no significant effects of photoperiod on LH concentration at 26, 33, 40 and 54 weeks (P > 0.05). The LH concentration of group 3 was significantly lower than those in the other 5 groups at 47 weeks (P < 0.05). Figure 1(c) shows that the serum E2 concentration was 34–58 pg/ml for 26–40 weeks, increased at 41 weeks, reached more than 100 pg/ml during weeks 47–54 before decreasing after 61 weeks. There were significant effects of photoperiod on E2 concentration (P < 0.05). The E2 concentrations of groups 1 and 3 were significantly lower than those in groups 5 and 6 (P < 0.05) at 33 weeks of age. The E2 concentrations of groups 3 and 4 were significantly higher than those in groups 5 and 6 (P < 0.05) at 40 weeks of age. At 47 weeks of age, the E2 concentration of groups 1 and 5 were significantly higher than those in groups 2, 3, 4 and 6 (P < 0.05). Figure 1(d) shows that serum Mel concentration did not change at different egg-laying stages (P > 0.05). The Mel concentration of group 1 was significantly higher than that of groups 2, 3 and 5 (P < 0.05), but lower than that of group 6 (P < 0.05) at 47 weeks of age. Figure 2 shows that serum P4 concentration was unchanged at different egg-laying stages. The P4 concentrations of groups 1 and 3 were significantly higher than in groups 5 and 6 at 33 weeks of age (P < 0.05), and the P4 concentration of group 1 was significantly higher than in group 2 at 40 weeks (P < 0.05). At 47 weeks of age, the P4 concentration of group 1 was significantly higher than in groups 3, 5 and 6 (P < 0.05) and lower than in groups 2 and 4 (P < 0.05). Correlations between traits are presented in Table 2, which shows that there was a strong positive relationship between broodiness rate and PRL concentration (r > 0.70), but for broodiness rate and other hormones, there was no strong positive relationship (r < 0.70). The correlation coefficient between broodiness rate and hormone concentrations was influenced by photoperiod, especially for rE2 and rP4 (P < 0.05). Group 1’s rE2 was significantly higher than for other groups (P < 0.05), and rP4 for group 5 was significantly higher compared with the other groups (P < 0.05). The correlation coefficient between egg-laying rate and hormone concentrations was not influenced by photoperiod, as shown in Table 3.
DISCUSSION Broodiness is one of the maternal expressions of female birds. Different breeds have a different prevalence of broodiness such as 30–50% for turkeys (Gueméné and Williams, 1994; Leighton
PHOTOPERIOD ON BROODINESS AND EGG-LAYING
20–26
27–33
34–40
41–47
48–54
55–61
GLM analysis Photoperiod
P-value Stage (weeks)
P-value Photoperiod × stage P-value
1 2 3 4 5 6 20–26 27–33 34–40 41–47 48–54 55–61
54.2fgh 59.0bcdefgh 52.0gh 48.4h 53.0fgh 52.6fgh 74.4ab 76.8a 77.5a 73.5ab 76.9a 70.6abcd 71.9ab 70.9abcd 71.3abc 68.6abcdef 70.2abcde 67.3abcdefg 53.8fgh 57.7c 55.8c 54.0fgh 59.3bcdefg 52.9c 49.8h 56.9c 55.3defgh 47.0h 57.4c 48.6h 47.4h 56.4c 54.5efgh 50.1h 54.2fgh 54.7efgh 0.94
Arcsine transformation 3.1b 2.8b 5.9a 4.2b 3.7b 3.1b 0.002 0.5d 2.8c 5.4b 9.9a 3.1c 0.9d 0.001 0.223
58.4b 62.9a 61.1ab 54.9b 61.7a 57.9b 0.054 53.2b 74.8a 70.0a 55.6b 52.5b 52.9b 0.001 0.165
Photoperiodic treatments: 1, 16L:8D (0600 to 2200 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (0300 to 1900 h); 5, 14L:10D; 6, 18L:6D. a,b,c Within a column, values not sharing a common superscript letter are significantly different (P < 0.05).
et al., 2001), 78% for bantam hens (Romanov et al., 2002), 17–18% for Muscovy duck (Lin,
Prolactin, ng/ml
0.9hi 0i 0i 0i 0.9hi 0.9hi 1.9ghi 1.9ghi 4.6defgh 2.8fghi 3.7efghi 1.9ghi 3.7efghi 4.6defgh 8.3bcd 6.5def 5.6efg 3.7efghi 8.3bcd 7.4ce 14.8a 11.1b 10.2bc 7.4ce 2.8fghi 1.9ghi 5.6d 3.7efhi 1.9ghi 2.8fhi 0.9hi 0.9hi 1.9ghi 0.9hi 0i 0.9hi 0.37
2
3
4
5
6
230 200 170 140 110 80 50 20 26
33
40 47 Age, weeks
b 1 Luteinising hormone, ng/ml
1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 SEM
Broodiness rate (%)
Egglaying rate (%)
2
3
4
54
61
5
6
10 8 6 4 2
26
33
40
47
54
61
Age, weeks
c 1
2
3
4
5
6
230 Oestradiol, pg/ml
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Photoperiodic treatments
Egglaying stage (weeks)
1
a
180 130 80 30
26
33
40 47 Age, weeks
1
d Melatonin, ng/ml
Effects of photoperiod and stage on broodiness rate and egg-laying rate of Beijing You laying hens
2
3
54
4
61
5
6
360 330 300 270 240 210 180 150 120 90 26
33
40 47 Age, weeks
54
61
Figure 1. Average serum concentrations of PRL (a), LH (b), 17-beta-oestradiol (E2) (c) and Mel (d) in laying hens under different photoperiodic treatments: 1, 16L:8D (0600 to 2200 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (0300 to 1900 h); 5, 14L:10D; 6, 18L:6D.
2005) and 15% for Qingyuan chickens (Jiang et al., 2010). Different egg-laying stages also affect the incidence of broodiness. Guemene and 1 Progesterone, ng/ml
Table 1.
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2
3
4
5
6
80 60 40 20 0
26
33
40 47 Age, weeks
54
61
Figure 2. Average P4 concentration in laying hens under different photoperiodic treatments: 1, 16L:8D (0600 to 2200 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (0300 to 1900 h); 5, 14L:10D; 6, 18L:6D.
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Table 2. Groups 1 2 3 4 5 6 P-value
Effects of photoperiod on correlation coefficients between broodiness rate and endocrine hormones Photoperiodic treatments
16L:8D (6:00–22:00) 12L:2D:4L:6D (6:00–18:00, 20:00–24:00) 8L:4D:4L:8D (6:00–14:00, 18:00–22:00) 16L:8D (3:00–19:00) 14L:10D (6:00–20:00) 18L:6D (6:00–24:00)
rPRL 0.85 0.81 0.82 0.82 0.92 0.76 0.055
rLH 0.12 0.16 0.01 0.28 0.24 0.09 0.061
rE2 a
0.60 0.14b 0.28b 0.32b 0.39b 0.29b 0.044
rMel
rP4
0.89 0.35 0.57 0.94 0.67 0.92 0.062
0.42b 0.35c 0.50b 0.60ab 0.74a 0.51b 0.045
Photoperiodic treatments: 1, 16L:8D (06:00 to 22:00 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (03:00 to 19:00 h); 5, 14L:10D; 6, 18L:6D. PRL, prolactin; LH, luteinising hormone; E2, 17-beta-oestradiol; Mel, melatonin; P4, progesterone. a,b.c Within a column, values not sharing a common superscript letter are significantly different (P < 0.05).
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Table 3.
Effects of photoperiod on correlation coefficients between egg-laying rate and endocrine hormones
Groups
Photoperiods
rPRL
rLH
rE2
rMel
rP4
1 2 3 4 5 6 P-value
16L:8D (6:00–22:00) 12L:2D:4L:6D(6:00–18:00, 20:00–24:00) 8L:4D:4L:8D (6:00–14:00, 18:00–22:00) 16L:8D (3:00–19:00) 14L:10D (6:00–20:00) 18L:6D (6:00–24:00)
0.29 0.39 0.15 0.18 0.42 0.26 0.062
0.77 0.86 0.81 0.65 0.71 0.85 0.058
−0.51 −0.70 −0.69 −0.53 −0.43 −0.70 0.072
0.38 0.66 0.65 0.17 0.77 0.01 0.075
0.83 0.89 0.71 0.67 0.69 0.54 0.057
Photoperiodic treatments: 1, 16L:8D (06:00 to 22:00 h); 2, 12L:2D:4L:6D; 3, 8L:4D:4L:8D; 4, 16L:8D (03:00 to 19:00 h); 5, 14L:10D; 6, 18L:6D. PRL, prolactin; LH, luteinising hormone; E2, 17-beta-oestradiol; Mel, melatonin; P4, progesterone.
Williams (1994) studied the broodiness index and plasma concentrations of PRL, LH, oestradiol and P4 throughout the first period of laying in turkey hens, and found that there was a significant effect of laying stage. The present study indicated that the average broodiness rate of BYC was 5.9% during the complete egg-laying stage (20–62 weeks), and there were different broodiness rates at different egg-laying stages. With the rapid increase of egg-laying during 27–33 weeks and 34–40 weeks, the broodiness rate also increased and the highest broodiness rate (9.9%) occurred during 41–47 weeks. The effect of photoperiod on birds is mainly reflected in its regulation of PRL concentration (Johnston, 2004). As a key mediator of seasonal breeding, PRL plays an important role in neuroendocrine regulation (Sharp and Blache, 2003). Proudman (1998) observed that the turkey’s PRL concentration was higher under a long photoperiod compared with a short photoperiod. In this study, photoperiodic group 2 showed the lowest rate of broodiness (2.8%) and the highest egg-laying rate (62.9%), which suggests that the photoperiod 12L:2D:4L:6D is optimal for the birds’ performance. The reason for this result may be due to optimal PRL and LH concentrations mediated by the photoresponsiveness of the birds. Photoperiodic group 3 had the highest rate of broodiness (5.9%), but its egg-laying rate (61.1%) was not significantly different from the other groups, which suggests that the higher broodiness rate was partially compensated for by a
greater rate of egg-laying in the non-broody periods or by non-broody hens (Jiang et al., 2010). Burke and Dennison (1980) reported that the PRL concentration was low (22 ng/ml) before the lighting stimulus and gradually increased to 45– 50 ng/ml at first egg, reaching 100 ng/ml or more in the initial egg-laying stages. There was a circadian rhythm for bantam hen PRL secretion, and PRL concentration was lower during the day than at night under a long photoperiod (Lea et al., 1981; Curlewis, 1992). Huang et al. (2008) reported that plasma PRL concentration of Magang geese was low in the breeding season (approximately 10 ng/ml) and rose to higher concentration (between 20 and 30 ng/ml) in the non-breeding season under the long photoperiod. LH concentration was initially high (between 1 and 2 ng/ml) and then decreased to concentrations below 1 ng/ml. In this study, there were no significant effects of photoperiod on PRL, LH and Mel concentration at 26, 33, 40 and 54 weeks of age, but at 47 weeks of age, PRL and LH concentrations in group 1 were significantly lower than those in the other groups. E2 and P4 concentrations in group 1 were significantly different from those in groups 2, 3, 4 and 6. Huang et al. (2008) proposed that PRL secretion was positively correlated with photoperiod for Magang geese. The present study found that the broodiness rate and PRL concentration had a strong correlation (r > 0.70). The correlation coefficient was also influenced by the photoperiod, and further research is
PHOTOPERIOD ON BROODINESS AND EGG-LAYING
needed to discover the mechanism of this relationship. Conclusion
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The present study suggests that the photoperiodic group 2 (12L:2D:4L:6D) is optimal for laying performance, for which it gives the lowest rate of broodiness and the highest rate of egg laying during the whole laying period. This may be due to optimal PRL and LH concentrations mediated by the photoresponses of the birds. Group 3 (8L:4D:4L:8D) had the highest rate of broodiness (5.9%), but its egg-laying rate showed no significant difference compared with the other groups, which suggests that the highest broodiness rate is not always associated with the lowest rate of overall egg-laying. The present study also suggests that 41–47 weeks may be a key stage for the photomodulation of broodiness.
ACKNOWLEDGEMENTS The authors wish to thank the National Natural Science Funds [grant number 30972128] and Beijing Natural Science Funds [grant number 6102010] for providing financial supports, Mr Liu Zhengkang for animal keeping and Ms Xiaolin Shi for some detailed observations on site.
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