饲喂过瘤胃褪黑素对荷斯坦奶牛乳中褪黑素与其合成前体和代谢产物含量、褪黑素合成酶活性及生产性能的影响

Effects of Feeding Rumen Protected Melatonin on Contents of Melatonin,Its Synthetic Precursors and Metabolites,Melatonin Synthase Activity in Milk and Performance of Holstein Dairy Cows

本试验旨在探究过瘤胃褪黑素(RPMT)对荷斯坦奶牛乳中褪黑素(MT)与其合成前体和代谢产物含量、MT合成酶活性及生产性能的影响。选取1~4胎次、泌乳天数在200 d以内的健康荷斯坦奶牛32头,随机分为4组,分别为对照组与试验Ⅰ、Ⅱ和Ⅲ组,每组8头。对照组饲喂正常全混合日粮(TMR),试验组在对照组饲粮的基础上分别添加140、160、180 mg/(头·d)RPMT,于每天14:00进行口腔投喂。试验期32 d,其中第0天为饲喂前1 d,第1~28天为饲喂期,第29~31天为停饲后3 d。试验组与对照组每日挤奶3次,分别在06:00、13:00和21:00。生产性能测定体系检测的乳样采样时间分别为第0、14、29天,MT含量及其他指标检测的乳样采样时间分别为第0、3、7、14、21、28、29、31天。结果表明:1)试验Ⅰ组06:00的乳脂率显著高于对照组与试验Ⅲ组(P<0.05),试验Ⅱ、Ⅲ组13:00的乳脂率显著高于对照组(P<0.05);试验Ⅱ、Ⅲ组13:00和21:00的乳糖率均显著高于对照组(P<0.05);同时,试验Ⅱ、Ⅲ组06:00和21:00的乳中体细胞数(SCC)均显著低于试验Ⅰ组(P<0.05),13:00的SCC显著低于对照组(P<0.05)。在06:00时,时间对乳糖率具有极显著影响(P<0.01),在13:00时,时间对乳脂率具有显著影响(P<0.05),组别与时间对乳糖率具有显著交互效应(P<0.05)。在21:00时,时间对上述指标均无显著影响(P>0.05),组别与时间也无显著交互效应(P>0.05)。2)试验Ⅲ组06:00、13:00和21:00的产奶量均极显著高于对照组与试验Ⅰ、Ⅱ组(06:00除外),但时间对产奶量无显著影响(P>0.05),组别与时间也无显著交互效应(P>0.05)。3)各试验组06:00、13:00和21:00的乳中谷胱甘肽过氧化物酶(GSH-Px)、超氧化物歧化酶(SOD)活性均极显著高于对照组(P<0.01),而试验Ⅲ组仅在21:00的乳中吲哚胺2,3-双加氧酶(IDO)活性显著高于对照组(P<0.05)和极显著高于试验Ⅰ组(P<0.01)。在06:00、13:00时,时间对乳中GSH-Px、SOD活性均具有极显著影响(P<0.01);在21:00时,时间对乳中GSH-Px、SOD及IDO活性均具有极显著影响(P<0.01),组别与时间对乳中IDO活性也具有极显著交互效应(P<0.01)。4)各组间06:00、13:00的乳中MT、6-羟基-褪黑素(6-OH-MT)含量及5-羟色胺-N-乙酰基转移酶(SNAT)、咖啡酸-O-甲基转移酶(COMT)及N-乙酰基-5-羟色胺-甲基转移酶(ASMT)活性均无显著差异(P>0.05),而试验组21:00的乳中MT、5-羟色胺(5-HT)、6-OH-MT含量及SNAT、COMT及ASMT活性均极显著高于对照组(P<0.01)。在06:00时,时间对乳中6-OH-MT含量具有极显著影响(P<0.01),在06:00与13:00时,时间对乳中SNAT活性具有显著影响(P<0.05);在21:00时,时间对乳中MT、5-HT、6-OH-MT含量和SNAT、COMT、ASMT活性均具有极显著影响(P<0.01),组别与时间对乳中MT、5-HT含量具有极显著交互效应(P<0.01),对乳中6-OH-MT含量及SNAT、COMT、ASMT活性均具有显著交互效应(P<0.05)。结果提示,给荷斯坦奶牛饲喂RPMT能够提升乳中乳脂率、乳糖率,同时RPMT饲喂量越大时,产奶量越高,SCC越低;给荷斯坦奶牛提供外源RPMT能够提高泌乳期奶牛抗氧化能力,增加乳中MT合成,同时乳中MT合成前体物5-HT与代谢产物6-OH-MT及MT合成酶活性会随着MT含量而变化,即MT合成与代谢具有同步性。

This experiment was conducted to investigate the effects of rumen protected melatonin(RPMT)on contents of melatonin(MT),its synthetic precursors and metabolites,MT synthase activity in milk and performance of Holstein dairy cows.Thirty-two healthy Holstein dairy cows with 1 to 4 parities and lactation days less than 200 days were randomly divided into 4 groups,including control group,test groupⅠ,test groupⅡand test groupⅢ,with 8 cows in each group.The control group was fed a normal total mixed diet(TMR),and the test groups were fed 140,160 and 180 mg RPMT on the basis of the control group for one day one cow.Each additive was orally fed at 14:00 every day,respectively.The experiment lasted for 32 days,including the day 0 was one day before feeding,the days 1 to 28 was feeding period,and the days 29 to 31 was three days after stopping feeding.Milking 3 times a day,06:00,13:00 and 21:00,respectively.The sampling time of Dairy Herd Improvement(DHI)was 0,14 and 29 days,and the sampling time of milk samples for MT content and other indexes was 0,3,7,14,21,28,29 and 31 days.The results showed as follows:1)the milk fat rate in test groupⅠat 06:00 was significantly higher than that in control group and test groupⅢ(P<0.05);the lactose rate at 13:00 and 21:00 in test groupⅡand test groupⅢwas significantly higher than that in control group(P<0.05),and the milk fat rate at 13:00 was significantly higher than that in control group(P<0.05).Meanwhile,milk somatic cell count(SCC)in test groupⅡand test groupⅢwas significantly lower than that in test groupⅠat 06:00 and 21:00(P<0.05)and that was significantly higher than that in the control group at 13:00(P<0.05).At 06:00,time had extremely significant effect on lactose rate(P<0.01),at 13:00,milk fat rate had significant effect(P<0.05),group and time had significant interaction effect on lactose rate(P<0.05).At 21:00,time had no significant effect on the above indexes(P>0.05),and group and time had no significant interaction effect(P>0.05).2)The milk yield in test groupⅢat06:00,13:00 and 21:00 was significantly higher than that in control group and test groupⅠand test groupⅡ(except 06:00),but time had no significant effect on milk yield(P>0.05),and there was no significant interaction between group and time(P>0.05).3)The activities of glutathione catalase(GSH-Px)and superoxide dismutase(SOD)in milk in experimental groups at 06:00,13:00 and 21:00 were significantly higher than those in control group(P<0.01),while milk indoleamine 2,3-dioxygenase(IDO)activity in test groupⅢat 21:00 was significantly higher than that in control group(P<0.05)and extremely significantly higher than that test groupⅠ(P<0.01).At 06:00 and 13:00,time had extremely significant effects on GSH-Px and SOD activities in milk(P<0.01).At 21:00,time had extremely significant effects on the activities of GSHPx,SOD and IDO in milk(P<0.01),group and time also had extremely significant interaction effects on the activities of IDO in milk(P<0.01).4)At 06:00,13:00,there were no significant differences in the contents of MT,6-hydroxy-melatonin(6-OH-MT)and the activities of 5-hydroxytryptamine-N-acetyltransferase(SNAT),caffeine-o-methyl transferase(COMT)and N-acetyl-5-hydroxytryptamine-methyltransferase(ASMT)in milk among groups(P>0.05),while the contents of MT,5-hydroxytryptamine(5-HT),6-OHMT and the activities of SNAT,COMT and ASMT in milk in test groups at 21:00 were significantly higher than those in control group(P<0.01).The content of 6-OH-MT in milk was significantly affected by time at06:00(P<0.01),and the SNAT activity was significantly affected by time at 06:00 and 13:00(P<0.05).At 21:00,time had extremely significant effects on the contents of MT,5-HT and 6-OH-MT and the activities of SNAT,COMT and ASMT(P<0.01),group and time had extremely significant interaction effects on the contents of MT and 5-HT in milk(P<0.01).There were significant interaction effects on 6-OH-MT content and activities of SNAT,COMT and ASMT in milk(P<0.05).The results indicate that RPMT feeding for Holstein dairy cows can improve milk fat rate and lactose rate in milk,and the higher the RPMT feeding amount is,the higher the milk yield is,the lower the SCC is.Providing exogenous RPMT to Holstein dairy cows during lactation can improve antioxidant capacity and increase MT synthesis in milk.Meanwhile,the contents of precursor of MT synthesis and 6-OH-MT metabolite and MT synthase activity in milk will change with MT content,that is,MT synthesis and metabolism have synchronization.