Construction of Novel Beef Production System : study of the effect of metabolic imprinting during the early growth period

和牛（日本黑牛）以其优质大理石牛肉而闻名，使用大量进口谷物饲料。本研究旨在将代谢印记系统的作用应用于肉牛生产中，通过代谢印记调节牛的体质，在不使用进口饲料的情况下，利用国产牧草资源，实现优质肉牛的生产。R组在屠宰前（26月龄）只喂粗饲料（干草），C组在2 ~ 10月龄喂精饲料（谷物），然后只喂粗饲料直至屠宰。我们在生长过程中通过活组织检查采集肌肉样本。实时荧光定量PCR检测肌内脂肪形成和肌肉发育相关基因的表达，10月龄后C组平均体重（265±18 kg）是R组（117±12 kg）的2.2倍（p<0.001）。屠宰时，C组体重（472±42 kg）仅为R组（357±25 kg）的1.3倍（p<0.001）。在背最长肌中，两组肌肉生长过程中肉质和肉质相关基因的mRNA表达量存在显著差异，说明生长早期的饲养水平影响骨骼肌中肉质和肉质相关基因的mRNA表达。试验组间生长量、产肉量和肉品质差异显著。这可能是由于在生长早期高饲养水平诱导的代谢印记效应造成的。

Wagyu (Japanese Black cattle) are known for their excellent marbled beef by using a considerable amount of imported grain feed. We would like to apply effects of metabolic imprinting system to beef production : we would like to realize a good quality production system that by regulating the constitution of cattle by metabolic imprinting and feeding domestic grass resources can produce safe beef in Japan without using imported feed.We investigated the effects of metabolic imprinting during the early growth period on meat quality by comparing between two groups of Wagyu steers; group R was fed only roughage (hay) until slaughter (26 mo), while the other group C was fed concentrate (grain) from 2 to 10 mo of age and then fed only roughage until slaughter. We took muscle samples by biopsy during growth. Gene expressions related to intramuscular adipogenesis and muscle development were investigated by real-time PCR.The average live weight was 2.2-fold higher in group C (265±18 kg) than in group R (117±12 kg) just after 10 mo of age (p<0.001). At slaughter, group C was just 1.3-fold heavier (472±42 kg) than group R (357±25 kg) (p<0.001). In longissimus muscles, there were significant differences of the mRNA expressions of meat quality-and quantity related genes during growth between these two groups.In conclusion, the feeding level during the early growth stage influenced mRNA expressions in skeletal muscle. The growth size, meat quantity and quality were markedly different between groups. This may be caused by the effect of metabolic imprinting induced by a high feeding level during the early growth stage.