Hypothalamic gene expressions of meat- and egg- type hens under different energy statuses and effects of dietary glycine supplementation on growth performance and related physiology of Roman geese

• Main Authors: Chia-Chun Lin, 林嘉雋
• Other Authors: Shuen-Ei Chen
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/5eas4g

碩士 === 國立中興大學 === 動物科學系所 === 100 === Along the history, chickens have been domesticated around 8000 years and populations bred for egg laying and meat production can be dated to about 100 years ago. During the twentieth century, growth performance (meat production) and reproductive efficacy (egg production) were further diverged to produce the modern layer and broiler strains. In order to explore the pathways that achieve the distinctively different phenotypes between egg-and meat-type chickens along domestication, in feeding trial 1 broiler breeder and ISA Brown layer hens were fed with restricted (130g/d) (BR) or ad libitum (BA) feeding and restricted (110g/d) (LR) or overfeeding (143g/d) (LO), respectively, for after 21 days to mimic domestication with sufficient fuel supply in contrast to their ancestors with semi-hunger status in the wild. Layers with overfeeding and broiler breeders with ad libitum feeding exhibited higher body weight, absolute and relative liver and abdominal fat weight and plasma glucose levels, but lower activation of AMPK (AMP-activated protein kinase) in the hypothalamus, suggesting obesity development in birds with higher energy status. A higher plasma norepinephrine levels was observed in BA birds than BR birds, but the difference was absent between LO and LR layers, suggesting that broiler breeders may keep adrenergic sensitivity in response to fuel stress. In contrast to birds with lower energy status (BR and LR), hypothalamic LKB1, SIRT1 and PGC-1α gene expression and pulsatile pattern were affected by higher energy status, leading to altered expression and pulsatile pattern of circadian genes in the hypothalamus including Bmal1, Clock, Cry, Per, E4bp4 and RORα and gonadotropin-releasing hormone (GnRH). These results thus may mimic the process that fuel saturation along domestication can drive the divergence of genetic pathways to achieve different phenotypes such as feeding behaviors, locomotor activities, metabolic regulations, stress adaptation that allow selection to proceed and thereby deviate to produce the modern chickens of egg- and meat-type strain. Taiwan is located in tropical and subtropical regions with high temperature and relative humidity under summer season. Finishing geese tend to have poor appetite during hot seasons in Taiwan, which impacts economical benefit. Glycine acts as a co-agonist of the N-methyl- D-aspartic acid (NMDA) receptors through excitatory neurotransmission to increase appetite. In order to increase feed intake of finishing geese during hot seasons in Taiwan, in feeding trial 2, geese at age of 8 weeks were fed diet supplemented with different levels of glycine (0%, 1%, 2% and 4% of feed) for 4 weeks during August and September. Results suggested that dietary supplementation of glycine, particularly at 2% level, significantly promoted daily feed efficiency and BW gain, but 2% level also significantly decreased fractional breast muscle weight. In plasma parameters, glycine inclusion exerted no significant effect on plasma glucose, non-esterified fatty acid (NEFA), triglyceride (TG) and uric acid level. Gene expressions relative to lipogenesis (acetyl-CoA carboxylase, fatty acid synthase, PPAR-γ and SREBP-1) in the leg muscle, breast muscle, liver, and adipose tissue and myogenic gene expressions (IGF-1, growth hormone receptor, myostatin, leucyl-tRNA synthetase) in the breast muscle were increased by dietary supplementation of lower glycine levels, but suppressed by the inclusion of a higher glycine level. Interestingly, hypothalamic neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF) and melanocortin 4 receptors (MC4R) expression was suppressed by dietary supplementation of glycine, suggest that glycine inclusion of feed decreased feed intake but had no effects on appetite gene expression. We concluded that dietary supplementation of glycine at 2% is the best recommendation use to promote geese growth performance during finishing period. Inconsistent results between NPY and BDNF expression suggest that other hypothalamic anorexigenic/orexigenic factors behind those examined in the current study are involved in regulating appetite by dietary glycine supplementation.