饲粮蛋氨酸水平对羔羊肝脏及血清中蛋氨酸循环代谢相关指标的影响

摘要

本试验旨在研究饲粮蛋氨酸水平对羔羊肝脏及血清中蛋氨酸循环代谢相关指标的影响.利用配对试验设计方法, 选取平均体重为 (4.93±0.20) kg的12对7日龄断母乳湖羊双胞胎公羔, 每对双胞胎羔羊分别分到2组中, 试验分2个阶段进行.第1阶段 (8～56日龄) , 2组羔羊分别补充[饲喂基础代乳粉+0.70％蛋氨酸、基础开食料+0.40％蛋氨酸, 对照组 (CON组) ]和限制蛋氨酸[饲喂基础代乳粉、基础开食料, 低蛋氨酸组 (LM组) ].第2阶段 (57～84日龄) , 2组羔羊停止饲喂基础代乳粉, 继续饲喂相同的补充蛋氨酸饲粮 (基础开食料+0.40％蛋氨酸) .在56和84日龄, 各选取6对双胞胎羔羊进行屠宰, 采集血液和分离肝脏并液氮保存用于测定蛋氨酸循环代谢相关指标.结果表明:1) 56日龄时, LM组羔羊肝脏中蛋氨酸含量显著高于CON组 (P<0.05) , 且LM组肝脏中S-腺苷甲硫氨酸 (SAM) /S-腺苷同型半胱氨酸 (SAH) 值显著高于CON组 (P<0.05) ; 84日龄时, LM组羔羊肝脏中蛋氨酸、SAM和SAH含量均显著低于CON组 (P<0.05) .2) 56日龄时, LM组羔羊肝脏中除甜菜碱-同型半胱氨酸S-甲基转移酶 (BHMT) 活性显著低于CON组 (P<0.05) 外, 2组间其他蛋氨酸循环代谢关键酶的活性均无显著差异 (P>0.05) ; 84日龄时, LM组羔羊肝脏中BHMT、甲硫氨酸腺苷转移酶 (MAT) 和甘氨酸-N-甲基转移酶 (GNMT) 活性均显著低于CON组 (P<0.05) .3) 56和84日龄时, LM组羔羊血清中蛋氨酸和SAM含量均显著低于CON组 (P<0.05) , 而2组在SAH和同型半胱氨酸 (Hcy) 含量上均差异不显著 (P>0.05) .由此可见, 饲粮中低蛋氨酸水平虽显著降低了羔羊肝脏中BHMT活性及血清中蛋氨酸和SAM含量, 却激发了肝脏中蛋氨酸的生成, 同时显著影响到肝脏SAM/SAH值, 使体内甲基供体水平下降, 影响羔羊正常甲基代谢;恢复饲粮蛋氨酸水平后, 肝脏及血清中蛋氨酸循环代谢相关指标等表观性状未能完全随蛋氨酸的补充而恢复.%The aim of this study was to assess the effects of dietary methionine (Met) level on methionine cycle metabolism-related indicators in liver and serum of lambs.Twelve pairs of male Hu twin lambs with an average body weight of (4.93±0.20) kg and weaned at 7 days of age were selected and divided into two groups with a matched-pairs experimental design, the experiment consisted of two stages.During the 1st stage (8 to 56 days of age) , lambs were fed diets containing either sufficient [basal milk replacer+0.70％ Met and basal starter+0.40％ Met, control (CON) group] or deficient Met [basal milk replacer and basal starter, low Met (LM) group].During the 2nd stage (57 to 84 days) , all lambs were stop feeding milk replacer and fed the same diet containing sufficient Met (basal starter + 0.40％ Met) .Blood samples of six twins were collected from jugular vein at 56 and 84 days of age before the lambs slaughtered, and they were slaughtered at 56 and84 days of age for separating liver and liquid nitrogen preservation.The blood and liver samples were used to measured Met cycle metabolism-related indicators.The results showed as follows:1) the Met content and Sadenosyl methionine (SAM) /S-adenosyl-L-homocysteine (SAH) value in liver of lambs at 56 days of age in LM group were significantly higher than those in CON group (P<0.05) , but the contents of Met, SAM and SAH in liver of lambs at 84 days of age in LM group were significantly lower than those in CON groups (P<0.05) .2) At 56 days of age, no significant differences were observed in the key enzyme activities of Met cycle metabolism in liver of lambs between LM and CON groups (P>0.05) except betaine-homocysteine methyltransferase (BHMT) activity, which in LM group was significantly lower than that in CON group (P<0.05) ;at 84 days of age, the BHMT, methionine adenosyltransferase (MAT) and glycine N-methyltransferase (GNMT) activities in liver of lambs in LM group were significantly lower than those in CON group (P<0.05) .3) Serum Met and SAM contents of lambs at 56 and 84 days of age in LM group were significantly lower than those in CON (P<0.05) , but no significant differences were observed in the serum SAH and homocysteine (Hcy) contents between groups (P>0.05) .The results suggest that low dietary methionine level significantly decreases the activity of BHMT in liver and the contents of Met and SAM in serum, motivates the production of Met in liver, and significantly affect the SAM/SAH value in liver, decreases the level of body methyl donor, and then affects normal methyl metabolism of lambs;recovery of dietary methionine level, methionine metabolism cycle related indicators in liver and serum fail to fully restore with Met supplementation.