| The present study was initiated upon the finding that dietary supplementation of cysteamine to Sanhuang broiler breeder hens affected offspring growth during early posthatch development, accompanied with significant alterations in leptin secretion in hens. The existence of leptin in the egg was proved and the yolk and albumin contents of leptin were found to be modified by cysteamine. We therefore put forward a hypothesis that leptin may be involved in mediating the maternal effect of cysteamine on offspring growth in broiler chickens, probably through modifying hepatic leptin synthesis and action, and altering mRNA expression of key factors involved in hepatic lipid metabolism. Leptin in ovo administration was employed then to verify the hypothesis. The effects of leptin in ovo administration on embryonic development, hatch weight, early posthatch growth rate were observed. The alterations in metabolic and endocrine parameters, hepatic leptin and LEPR expression, as well as the mRNA expression profiles for the key factors involved in lipid metabolism, including SREBP, FAS, ACC and ApoB, were characterized.1 Leptin is involved in the effect of cysteamine on egg laying of hens and posthatch growth of broiler offspringCysteamine has been reported to modulate lipid metabolism and energy homeostasis and exert significant growth promoting effects on broiler chickens. However, little is known concerning its effects on egg production of hens and the growth rate of their offspring. In the present study,67-week-old broiler breeder hens were allotted at random to control and cysteamine-supplemented (400 mg/Kg) groups for 8 weeks. The hatchlings were fed under the same condition till 6 weeks of age. Cysteamine significantly increased the average laying rate by 2.24%(P<0.01), decreased dramatically the percentage of the broken eggs by 40.55%(P< 0.01), while increased that of the abnormal eggs by 20.15%(P<0.05). Cysteamine did not alter the egg weight, egg quality, fertility or hatchability, but significantly increased eggshell weight (P<0.05) and decreased albumin weight (P<0.05). Serum concentrations of thyroxine (T4) (P<0.01) and leptin (P<0.01) were significantly lower in cysteamine-treated hens, while triiodothyronine (T3), free T3 and glucagon were not affected. Western blot analysis with leptin-specific antibody detected a band of approximately 15-16 KDa in egg yolk and albumin extracts as well as liver homogenates of hens. Cysteamine did not affect the yolk content of T3, T4, E2 or glucagon, but significantly increased leptin content in liver of hens (P<0.05), as well as in yolk (P<0.05) and albumin (P<0.05) of eggs. These changes were accompanied by a significant down-regulation of leptin receptor mRNA expression(P<0.05) in yolk sac of day 12 embryos. Female offspring hatched from cysteamine-treated eggs demonstrated significantly lower body weight at hatching (P<0.01) and 42 days of age (P<0.01). The results indicate that cysteamine improves laying performance of hens and affects the early posthatch growth of broiler offspring, in a gender-specific fashion. The modified leptin secretion and egg deposition, together with altered yolk sac leptin receptor expression may be involved in such an effect.2 Effects of in ovo leptin administration on embryo development and hepatic lipid metabolism in newly hatched broiler chickensLeptin in ovo administration was used in the present study to investigate the effect of leptin deposited in eggs on embryonic development and hepatic lipid metabolism in the chicken. Eggs purchased from Sanhuang broiler breeding farm were injected with either 0.5μg of recombinant mice leptin in 100μL of phosphate buffered saline (PBS) or 100μL PBS before incubation. Serum and liver samples were taken and fetal body weights were recorded on embryonic days 12 (E12) and E17 as well as at hatching (DO). Serum concentration of leptin was measured with radioimmunoassay. Hepatic expressions of leptin receptor and lipid metabolic genes were determined with Real-time RT-PCR, and LEPR protein content was detected with Western blot analysis. Chicks hatched from leptin-treated eggs showed lower hatch weight but higher liver index than the control group (P=0.000,0.018). Hepatic leptin content was increased in E12 and DO and so was the serum leptin concentration in DO. However, no differences were found in hepatic LEPR expression at either mRNA or protein levels. Liver contents of TG and Tch were decreased, whereas the opposite was true for serum levels of TG and Tch. This, combined with higher serum level of ApoB, suggests higher lipid transport from liver in leptin-treated group. Hepatic expression of ACC and FAS mRNA was not altered, but SREBP-1 mRNA expression was up-regulated significantly, suggesting a potential increase of fatty acid synthesis in the liver. It was noteworthy that in ovo leptin injection affected female chicks more significantly. These results suggest that in ovo leptin injection inhibits embryo development and decreases hatch weight, which may be associated with alterations in hepatic leptin synthesis and secretion, as well as hepatic lipid metabolism in newly hatched broiler chickens.3 Effect of in ovo leptin administration on early posthatch growth and hepatic lipid metabolism in broiler chickensLeptin in ovo administration was employed to investigate the dose-dependent effect of leptin deposited in eggs on early posthatch growth and hepatic lipid metabolism in the chicken. Breeder eggs were allocated to three groups and injected with 0.5μg (low leptin, LL),5.0μg (high leptin, HL) of recombinant mice leptin in 100μL of PBS or 100μL PBS (Control, Con) before incubation. The hatchings were raised under the same condition till 21 days (D21) of age when serum and liver samples were taken for analysis. Serum concentrations of leptin and thyroid hormones were measured with radioimmunoassay, hepatic expression of leptin receptor and lipid metabolic genes were determined with Real-time RT-PCR, and LEPR protein content was detected with Western blot analysis. Chicks treated with high or low doses of leptin in ovo had lower hatch weight than the control group, the differences being more significant in LL group and female chicks being more susceptible (P=0.042). However, the posthatch growth rate was higher in both leptin-treated groups compared to control group. At D21, chicks treated with leptin in ovo demonstrated significantly higher body weight than control group (P=0.042,0.003). Furthermore, male chickens in HL group showed higher width of intermuscular fat cingulum, which was accompanied with significantly higher hepatic and serum leptin (P= 0.036,0.053), increased serum FT3 (P=0.021) and T3 (P=0.034), as well as elevated hepatic and serum Tch. Hepatic expressions of SREBP-1, ACC, ApoB, GHR and IGF-I mRNA were found significantly up-regulated in male chickens of HL group (P=0.052, 0.017,0.010,0.028,0.020). These results indicate that in ovo administration of leptin inhibits embryo development but increase posthatch growth rate in broiler chickens with modifications in hepatic lipid metabolism. These effects were dependent on dose, gender and developmental stage. The females were more susceptible to low dose of leptin and affected more significantly before hatching, while the males were more susceptible to high dose of leptin and the effect were more pronounced after hatching. In addition, thyroid hormones and growth axis genes may be involved in the mechanism of leptin’s effects on posthatch growth and hepatic lipid metabolism in the chicken. |
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