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Leptin Is Involved in the Effects of Cysteamine on Egg Laying of Hens, Characteristics of Eggs, and Posthatch Growth of Broiler Offspring

Key Laboratory of Animal Physiology & Biochemistry, Nanjing Agricultural University, Nanjing 210095, P. R. China

¹ Corresponding author: Zhao.ruqian{at}gmail.com

Cysteamine has been reported to modulate energy homeostasis and exert significant growth-promoting effects in 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-wk-old broiler breeders were allotted at random to control and cysteamine-supplemented (400 mg/kg) groups for 8 wk. The hatchlings were fed under the same condition until 6 wk 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), and increased that of the abnormal eggs by 20.15% (P < 0.05). Cysteamine did not alter the egg weight, egg quality, fertility, or hatch-ability but significantly increased eggshell weight (P < 0.05) and decreased albumin weight (P < 0.05). Serum concentrations of total thyroxine (P < 0.01) and leptin (P < 0.01) were significantly lower in cysteamine-treated hens, whereas total triiodothyronine (T₃), free T₃, and glucagon were not affected. Western blot analysis with leptin-specific antibody detected a band of approximately 15 to 16 kDa in egg yolk and albumin extracts as well as in liver homogenates of hens. Cysteamine did not affect the yolk content of T₃, thyroxine, estradiol, 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 downregulation of leptin receptor mRNA expression (P < 0.05) in the yolk sac of d-12 embryos. Female offspring hatched from cysteamine-treated eggs demonstrated significantly lower body weight at hatching (P < 0.01) and 42 d 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 sex-specific fashion. The modified leptin secretion and egg deposition, together with altered yolk sac leptin receptor expression, may be involved in such an effect.

Key Words: cysteamine • laying performance • maternal effect • leptin • broiler chicken