添喂色氨酸、过瘤胃色氨酸对奶牛泌乳性能、血浆指标和乳中褪黑素含量的影响

本研究旨在探究在饲粮中添喂色氨酸(Trp)、过瘤胃色氨酸(RPTrp)对奶牛泌乳性能、血浆指标和乳中褪黑素(MLT)含量的影响。选取30头3~5岁、2~3胎次、泌乳天数为(180±46)d的健康荷斯坦奶牛,随机分为3组,分别为对照组、试验Ⅰ组和试验Ⅱ组,每组10头。对照组饲喂全混合日粮,试验Ⅰ、Ⅱ组在对照组基础上分别添喂100 g/(d·头)色氨酸和220 g/(d·头)过瘤胃色氨酸(L-色氨酸含量≥45%)。预试期7 d,正试期60 d。结果表明:1)试验Ⅰ、Ⅱ组产奶量相比于对照组分别提高了11.78%(P0.05)和17.19%(P0.01);试验Ⅰ、Ⅱ组乳糖产量极显著高于对照组(P0.01)。2)试验Ⅰ、Ⅱ组在14:00和22:00血浆中生长激素(GH)含量极显著高于对照组(P0.01);14:00时,试验Ⅱ组血浆色氨酸含量极显著高于对照组(P0.01),各组血浆褪黑素含量无显著差异(P0.05);22:00时试验Ⅱ组血浆色氨酸含量极显著高于对照组(P0.01),试验Ⅱ组血浆褪黑素含量显著高于对照组(P0.05);试验Ⅰ组在14:00和22:00血浆色氨酸、5-羟色胺(5-HT)和褪黑素的含量与对照组均无显著差异(P0.05)。3)05:00时试验Ⅱ组乳中褪黑素含量极显著高于对照组(P0.01);18:00时各组乳中褪黑素含量无显著差异(P0.05)。4)试验Ⅰ组血浆总抗氧化能力(T-AOC)极显著高于对照组(P0.01);试验Ⅱ组血浆谷胱甘肽过氧化物酶(GSH-Px)活性极显著高于对照组(P0.01);试验Ⅰ、Ⅱ组血浆超氧化物歧化酶(SOD)活性极显著高于对照组(P0.01);试验Ⅱ组血浆丙二醛(MDA)含量极显著低于对照组(P0.01)。结果提示,添喂色氨酸[100 g/(d·头)]、过瘤胃色氨酸[220 g/(d·头)]能够提高泌乳期奶牛产奶量、血浆GH含量及抗氧化能力,其中以添喂过瘤胃色氨酸效果较好;添喂过瘤胃色氨酸[220 g/(d·头)]可提高血浆色氨酸含量及夜间血浆褪黑素含量,从而提高夜间奶牛乳中褪黑素含量。

Effects of Tryptophan and Rumen-Protected Tryptophan Supplementations on Lactation Performance,Plasma Indexes and Milk Melatonin Content of Dairy Cows

This study was conducted to investigate the effects of tryptophan ( Trp) and rumen-protected trypto-phan ( RPTrp) supplementations in diet on lactation performance, plasma indexes and milk melatonin ( MLT) content of dairy cows. Thirty healthy Holstein dairy cows at 3 to 5 years of age, 2 to 3 parities, (180±46) d of lactation days were selected and randomly divided into 3 groups, which were control group, trial groupsⅠand Ⅱ. Cows in control group was fed a total mixed ration ( TMR) , and trial groups Ⅰ and Ⅱ were supple-mented with 100 g/( d·head) Trp and 220 g/( d·head) RPTrp [ L-tryptophan content was over 45%] based on control group, respectively. The pre-trial lasted for 7 days, and the trial lasted for 60 days. The results showed as follows:1) Compared with control group, milk yield in trial groups Ⅰ and Ⅱ was increased by 11.78% ( P<0.05) and 17.19% ( P<0.01) , respectively; lactose yield in trial groups Ⅰ and Ⅱ was signifi-cantly increased ( P<0. 01 ) . 2 ) Compared with control group, plasma growth hormone ( GH ) content at 14:00 and 22:00 in trial groups Ⅰ and Ⅱ was significantly increased( P<0.01); at 14:00, plasma Trp con-tent in trial groupⅡwas significantly increased ( P<0.01) , but there was no significantly difference of plasma MLT content among groups ( P>0.05);at 22:00, plasma Trp ( P<0.01) and MLT contents ( P<0.05) in tri-al group Ⅱ were significantly increased; in trial group Ⅰ, plasma Trp, 5-hydroxytryptamine ( 5-HT ) and MLT contents were not significantly changed both at 14:00 and 22:00 ( P>0.05) . 3) Compared with control group, at 05:00, milk MLT content in trial group Ⅱ was significantly increased ( P<0.01); at 18:00, there was no significant difference of milk MLT content among groups ( P>0.05) . 4) Compared with control group, plasma total antioxidant capacity (T-AOC) in trial group Ⅰ was significantly increased(P<0.05); plasma glutathione peroxidase (GSH-Px) activity in trial group Ⅱ was significantly increased(P<0.01); plasma su-peroxide dismutase (SOD) activity in trial groups Ⅰ and Ⅱ was significantly increased (P<0.01); plasma malondialdehyde ( MDA) in trial group Ⅱ was significantly reduced ( P<0.01) . In conclusion, supplementa-tion of Trp [100 g/(d·head)] and RPTrp [220 g/(d·head),] increases milk yield, plasma GH content and antioxidant capacity of Holstein dairy cows, and RPTrp shows better effect; supplement of RPTrp [ 220 g/( d·head) ] elevated plasma Trp content and plasma MLT contents at night of dairy cows, and hence increase MLT content in milk at the night.