过瘤胃γ-氨基丁酸（GABA）的研制及其对奶牛生产性能的影响与机理研究
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摘要
γ-氨基丁酸(GABA)是哺乳动物中枢神经系统中重要的神经递质,对动物具有多种调节功能。GABA在单胃动物上研究较多,但在反刍动物中研究报道很少。由于GABA在瘤胃内会被降解,本文首先开展了GABA的过瘤胃保护技术研究,研制出在瘤胃中较稳定、并能在瘤胃后有效释放的过瘤胃GABA(RP-GABA);然后研究了(?)P-GABA对围产期奶牛和泌乳盛期奶牛采食量和生产性能的影响,并从血液生理生化指标、采食相关基因表达等方面,探讨了GABA的作用机理。
1、过瘤胃GABA的研制(试验一)
由于GABA极易在瘤胃降解,因此首先对GABA进行过瘤胃包被加工研制。采用了L9(34)正交试验设计,以GABA的含量,被材种类和进料速度(压力)为变量,得到9种产品。以药物溶出法作为检测方法,筛选出四种溶出度较低的产品作为后续过瘤胃效果评定；然后采用体外法和半体外法进行评价,筛选出过瘤胃保护率和瘤胃后释放率较优的产品,并通过体外产气试验测定RP-GABA对瘤胃发酵参数的影响。结果显示：在瘤胃中放置2h后,GABA完全消失,而RP-GABA的消失率显著下降。瘤胃后消化率测定结果,样品残渣和RP-GABA样品的释放率都达到90%,说明RP-GABA在瘤胃后大部分可被释放。筛选出的四种样品可吸收率为90.8%-98.3%；综合产品的过瘤胃率,其总消化率分别为49.2%-75.8%。上述结果表明,在包被材料、进料压力和芯材含量三种因素中,包被材料对RP-GABA的稳定性起关键作用；RP-GABA对瘤胃发酵参数几乎没有影响。在GABA含量为50%、用固体棕榈油脂包被、压力11kp的条件下加工而成的RP-GABA,其过瘤胃保护率较高,且在下部消化道释放好。因此,后续试验均用该条件下调制的RP-GABA。
2、GABA对荷斯坦奶牛采食量和生产性能的影响
围产期和泌乳高峰期是泌乳奶牛的关键阶段,围产期奶牛采食量的上升滞后于奶量的上升,而泌乳高峰期的采食量也常不能满足高产的需要,所以改善这两个阶段的采食量至关重要。因此,本研究利用研制的RP-GABA,开展了围产期奶牛和泌乳高峰期奶牛的效果试验。
2.1GABA对围产期奶牛采食量和生产性能的影响(试验二)
根据上一胎次乳产量、预产期和胎次选择40头经产奶牛,按配对法均分为四组,第一组饲喂基础日粮(对照),第二组在基础日粮上添加0.6g/dGABA,第三和第四组分别在基础日粮中添加RP-GABA1.2g/d (GABA=0.6g/d)和2.4g/d(GABA=1.2g/d),试验期从产前2周至产后4周,每周测定乳产量和乳成分,每周测定奶牛采食量。结果发现,饲喂1.2g/d GABA可显著提高产后3-4周奶牛采食量(P<0.05),同时显著提高乳蛋白产量(P<0.05)。
2.2. GABA对泌乳盛期奶牛采食量和生产性能的影响(试验三)
根据乳产量、胎次选择泌乳盛期奶牛48头,按配对法均分为四个组,设置四个处理,分别为基础日粮(对照)、基础日粮添加RP-GABA0.8g/d,1.6g/d或2.4g/d(GABA添加量分别为0.4,0.8和1.2g/d)。试验期为8周。每周测定乳产量和乳成分,于第1、4、7周测定奶牛采食量。结果发现,试验组的干草采食量显著大于对照组(P<0.05),0.4g/d GABA组奶牛的奶产量显著高于对照组(P<0.05),而1.2g/d GABA组奶牛的奶产量与对照组无差异。0.4和0.8g/d GABA组奶牛乳蛋白产量显著高于对照组(P<0.05),乳脂率对照组与处理组间无差异。表明GABA可提高泌乳盛期奶牛采食量和生产性能。
可见,在日粮中添加GABA可提高奶牛干物质采食量,进而改善奶牛生产性能。
3、GABA促进奶牛采食量的机理研究
在单胃动物中,GABA主要通过神经肽Y (NPY)和胆囊收缩素(CCK)代谢通路对动物采食进行调控,但其在奶牛中作用机理尚不清楚。本研究通过血液代谢指标和采食相关基因mRNA丰度(以湖羊为模式动物)两个层面,对GABA在奶牛中的促采食机理进行了初步研究。
3.1GABA对奶牛血液代谢指标的影响(试验四)
在上述围产期奶牛的试验三中,每周采血样集,测定血浆代谢指标；在泌乳盛期奶牛试验(试验二)中,第1、4、7周采集血样,测定血浆代谢指标。结果发现,在围产期奶牛产后第三、四周,在日粮中添加1.2g/dGABA提高奶牛血清中过氧化物歧化酶(SOD)、GSH-Px、总抗氧化能力(T-AOC)浓度(P<0.05),降低奶牛血清中NEFA浓度,降低奶牛血中CCK浓度(P<0.05),各处理间血清NPY和leptin(瘦素)浓度均无差异。在泌乳盛期日粮中添加0.8g/dGABA可提高奶牛血清中谷胱甘肽还原酶(GSH-Px)活性(P<0.05),降低奶牛血清丙二醛(MDA)浓度(P<0.05); GABA组奶牛血清游离脂肪酸(NEFA)浓度显著低于对照组；血清NPY浓度在各组间无差异。上述结果提示,添加GABA可增强奶牛抗氧化能力,改善奶牛健康状况,可能通过CCK途径提高奶牛采食量。
3.2GABA对采食相关基因表达的影响(试验五)
根据体重选取断奶湖羊24只,按随机区组设计分为3个处理,每个处理4个重复(栏),每个重复2只羔羊。采用全混合日粮模式,在基础日粮上添加0mg/d(对照)、140mg/d和280mg/d的RP-GABA (GABA分别为0,70和140mg/d),试验期为42天,每周连续测定三次日采食量。在饲养试验结束时进行屠宰试验,取十二指肠和回肠粘膜上皮,测定采食相关基因mRNA丰度。结果发现,在日粮中添加140mg/d GABA可显著提高断奶湖羊采食量(P<0.05),并提高试验期4-6周湖羊日增重(P<0.05),显著提高十二指肠上皮GABA-B受体1nRNA丰度,抑制CCK-2受体的相对表达量(P<0.05)。提示在反刍动物中,GABA可能通过CCK途径,对采食量进行调控。
综上所述,包被材料是RP-GABA的稳定性关键因素；在日粮中添加GABA可提高围产期和泌乳盛期荷斯坦奶牛的采食量,进而提高其产奶性能,适宜的添加剂量分别为1.2g/d和0.6g/d。GABA对反刍动物的调控可能与CCK代谢通路有关。
Gama-aminobutyric acid (GABA) is one of the most important neurotransmitter in central nervous system, and has many regulatory functions on the animals. Many researches have been conducted with mono-gastric animals on the effects of GABA. However, there are few reports on ruminant animals. Due to the ruminal degradability of GABA, rumen-protected technology of GABA was developed to make GABA available in ruminants. A kind of rumen-protected (RP-GABA) which is stable in rumen but released efficiently in post-rumen digestive tracts was developed; the selected RP-GABA was then used to determine the effects of RP-GABA on feed intake and milk performance in transition and early lactating cows; finally, mechanisms of GABA on dairy cows were investigated by changes in serum variables and expression of feed intake related genes.
1. Preparation of RP-GABA (Trail1)
As GABA could be easily degraded in rumen, it should be protected before it can be applied in ruminant animals. The trail was conducted to prepare RP-GABA of high rumen-protected rate and intestinal digestive rate. Nine samples were designed and prepared, according to orthogonal design L9(34). GABA content, coating materials and air pressure were defined as the variations of preparation protocol. Dissolution rates were measured and four products with lower dissolution rates were selected to determine the ruminal and post-ruminal dissolution rates. The study was then conducted to estimate the dissolution rates of RP-GABA with the methods of in vitro and in sacco. All products had lower degraded rates than that of unprotected GABA (almost degraded within2h). Post-ruminal dissolution rates of the four products were over90%, indicating that they can be almost dissolved. All products had dissolution rates above90%in the digestive tract and the total digestive rates of were estimated to be from49.2%-75.8%. In summary, within the three factors (coating material, air pressure and GABA content), coating material played the key role in stability of RP-GABA. RP-GABA (50%GABA content, solid palm fatty acid pelled, air pressure11kp) was of low dissolution rate and high post-ruminal dissolution rate, and was selected to be used in all the following in vivo trails.
2. Effects of GABA on feed intake and lactating performance in Holstein dairy cows (Trail2and3)
Transition and early lactating are critical physiological periods for Holstein dairy cows. Feed intake of both transition and early lactating cows may not meet the requirements of the increasing milk yield. Thus, feed intake of these cows is a key issue for dairy nutrition. Thus, prepared RP-GABA was applied to investigate its effects on transition and early lactating cows.
2.1Effects of dietary GABA on feed intake and lactating performance in transition dairy cows (Trail2)
Transition cows:Forty multiparous cows were blocked based on previous milk production, parity, estimated calving date and body weight and were randomly assigned to one of four treatments and received either no GABA (control) or were supplemented with non-protected GABA (1.2g/day) or RP-GABA (1.2and2.4g/day (GABA=0.6and1.2, respectively)), respectively. The experiment lasted from2weeks before calving to4weeks after calving. Milk yield and milk composition were recorded weekly. The results showed that, during3rd and4th week, cows fed1.2g/d GABA had higher feed intake, and higher milk protein yield (4th week), compared with that of the control.
2.2Effects of dietary GABA on feed intake and lactation performance in early lactating dairy cows (Trail3)
Forty-eight multiparous cows were blocked based on days in milk (DIM), milk production and parity and were randomly assigned to one of four treatments with RP-GABA added at levels of0,0.8,1.6or2.4g/d (GABA=0,0.4,0.8, and1.2, respectively), respectively. The experimental period was8weeks. Milk yield and milk composition (fat, true protein, lactose) were recorded weekly. Results indicated that cows fed GABA consumed more grass hay (P<0.05). Cows consumed0.4g/d GABA were of higher milk yield (P<0.05), compared those of the control, but yielding off when cows consumed1.2g/d RP-GABA. Milk protein yield increased in the cows fed0.4or0.8g/d RP-GABA, respectively. No difference was observed in either fat or protein contents of milk. Cows fed0.4and0.8g/d GABA had higher lactose contents, compared with those of the control (P<0.05). In summary, dry matter intake and milk performance could enhanced dose-dependently in cows fed GABA.
In summary, GABA enhanced milk performance by increasing feed intake in Holstein dairy cows.
3The mechanism of GABA on dry matter intake in dairy cows (Trail4and5)
In mono-gastric animals, GABA mainly regulated feed intake through neuropeptide Y (NPY) and cholecystokinin (CCK) pathways. However, the mechanism is not clear in dairy cows. Thus, the current study was conducted to investigate the mechanism of GABA in feed intake regulation in dairy cows, by determining serum variables and genes expression related with feed intake (with Hu sheep as model).
3.1Effects of GABA on serum variables in dairy cows (Trail4)
In trail2, sera of transition cows were collected weekly. Serum contents of NPY, CCK, leptin and biochemical and antioxidative metabolites were analyzed weekly and the calving day. In trail3, sera of early lactating cows were collected in the1st,4th, and7th week, and serum contents of GABA, neuropeptide Y, and biochemical and antioxidant variables were analyzed. The results indicated that feeding1.2g/d GABA enhanced serum SOD (super oxide dismutase), GSH-Px (gluthathione peroxidase) and T-AOC (total antioxidation capacity) contents, decreased serum NEFA contents, and decreased serum CCK contents during3-4week after calving, compared with that of the control (P<0.05). No difference was observed in leptin among all treatments. For early lactating cows, animals fed0.8g/d GABA had higher GSH-Px and lower malondialdehyde (MDA) contents in sera, compared with those of the control (P<0.05). All cows fed GABA were of low NEFA contents (P<0.05). GABA did not change serum NPY contents in both studies. In summary, GABA enhanced anti-oxidative capacity and health condition. GABA enhanced feed intake through pathway related with CCK.
3.2Effect of GABA on gene expression related with feed intake (Trail5)
Twenty-four Hu lambs weaned at age of50d were divided into three groups of eight lambs each, with four units of two lambs in each group, based on body weight, and were randomly assigned to three dietary treatments with addition of RP-GABA at levels of0,140or280mg/d (GABA=0,70,140mg/d). Feeding trial lasted6weeks. The DMI was recorded weekly in three consecutive days. At the end of the trial, four lambs from each group were slaughtered, and duodenum and ileum mucosa were obtained from RNA abundance measurements of genes regulating feed intake. The result indicated that DMI was significantly higher (P<0.05) in the lambs fed140mg/d GABA than those of the control during the whole period. Compared with control, lambs fed140mg/d RP-GABA had higher mRNA abundance of GABA-B receptor (P<0.05) and lower mRNA abundance of CCK-2receptor (P<0.05) in duodenum mucosa. The results indicated that RP-GABA regulated dry matter intake by affecting mRNA abundances of GABA-B and CCK-2receptors in duodenum epithelia.
In summary, coating material could be the key factor in stability of the RP-GABA products. Addition of GABA enhanced feed intake and then milk performance in both transition and early lactating cows, respectively. The optimal doses of GABA were1.2and0.6g/d for transition cow and early lactating cows, respectively. Regulatory effect in feed intake induced by GABA might be related with CCK metabolic pathway.
1、过瘤胃GABA的研制(试验一)
由于GABA极易在瘤胃降解,因此首先对GABA进行过瘤胃包被加工研制。采用了L9(34)正交试验设计,以GABA的含量,被材种类和进料速度(压力)为变量,得到9种产品。以药物溶出法作为检测方法,筛选出四种溶出度较低的产品作为后续过瘤胃效果评定；然后采用体外法和半体外法进行评价,筛选出过瘤胃保护率和瘤胃后释放率较优的产品,并通过体外产气试验测定RP-GABA对瘤胃发酵参数的影响。结果显示：在瘤胃中放置2h后,GABA完全消失,而RP-GABA的消失率显著下降。瘤胃后消化率测定结果,样品残渣和RP-GABA样品的释放率都达到90%,说明RP-GABA在瘤胃后大部分可被释放。筛选出的四种样品可吸收率为90.8%-98.3%；综合产品的过瘤胃率,其总消化率分别为49.2%-75.8%。上述结果表明,在包被材料、进料压力和芯材含量三种因素中,包被材料对RP-GABA的稳定性起关键作用；RP-GABA对瘤胃发酵参数几乎没有影响。在GABA含量为50%、用固体棕榈油脂包被、压力11kp的条件下加工而成的RP-GABA,其过瘤胃保护率较高,且在下部消化道释放好。因此,后续试验均用该条件下调制的RP-GABA。
2、GABA对荷斯坦奶牛采食量和生产性能的影响
围产期和泌乳高峰期是泌乳奶牛的关键阶段,围产期奶牛采食量的上升滞后于奶量的上升,而泌乳高峰期的采食量也常不能满足高产的需要,所以改善这两个阶段的采食量至关重要。因此,本研究利用研制的RP-GABA,开展了围产期奶牛和泌乳高峰期奶牛的效果试验。
2.1GABA对围产期奶牛采食量和生产性能的影响(试验二)
根据上一胎次乳产量、预产期和胎次选择40头经产奶牛,按配对法均分为四组,第一组饲喂基础日粮(对照),第二组在基础日粮上添加0.6g/dGABA,第三和第四组分别在基础日粮中添加RP-GABA1.2g/d (GABA=0.6g/d)和2.4g/d(GABA=1.2g/d),试验期从产前2周至产后4周,每周测定乳产量和乳成分,每周测定奶牛采食量。结果发现,饲喂1.2g/d GABA可显著提高产后3-4周奶牛采食量(P<0.05),同时显著提高乳蛋白产量(P<0.05)。
2.2. GABA对泌乳盛期奶牛采食量和生产性能的影响(试验三)
根据乳产量、胎次选择泌乳盛期奶牛48头,按配对法均分为四个组,设置四个处理,分别为基础日粮(对照)、基础日粮添加RP-GABA0.8g/d,1.6g/d或2.4g/d(GABA添加量分别为0.4,0.8和1.2g/d)。试验期为8周。每周测定乳产量和乳成分,于第1、4、7周测定奶牛采食量。结果发现,试验组的干草采食量显著大于对照组(P<0.05),0.4g/d GABA组奶牛的奶产量显著高于对照组(P<0.05),而1.2g/d GABA组奶牛的奶产量与对照组无差异。0.4和0.8g/d GABA组奶牛乳蛋白产量显著高于对照组(P<0.05),乳脂率对照组与处理组间无差异。表明GABA可提高泌乳盛期奶牛采食量和生产性能。
可见,在日粮中添加GABA可提高奶牛干物质采食量,进而改善奶牛生产性能。
3、GABA促进奶牛采食量的机理研究
在单胃动物中,GABA主要通过神经肽Y (NPY)和胆囊收缩素(CCK)代谢通路对动物采食进行调控,但其在奶牛中作用机理尚不清楚。本研究通过血液代谢指标和采食相关基因mRNA丰度(以湖羊为模式动物)两个层面,对GABA在奶牛中的促采食机理进行了初步研究。
3.1GABA对奶牛血液代谢指标的影响(试验四)
在上述围产期奶牛的试验三中,每周采血样集,测定血浆代谢指标；在泌乳盛期奶牛试验(试验二)中,第1、4、7周采集血样,测定血浆代谢指标。结果发现,在围产期奶牛产后第三、四周,在日粮中添加1.2g/dGABA提高奶牛血清中过氧化物歧化酶(SOD)、GSH-Px、总抗氧化能力(T-AOC)浓度(P<0.05),降低奶牛血清中NEFA浓度,降低奶牛血中CCK浓度(P<0.05),各处理间血清NPY和leptin(瘦素)浓度均无差异。在泌乳盛期日粮中添加0.8g/dGABA可提高奶牛血清中谷胱甘肽还原酶(GSH-Px)活性(P<0.05),降低奶牛血清丙二醛(MDA)浓度(P<0.05); GABA组奶牛血清游离脂肪酸(NEFA)浓度显著低于对照组；血清NPY浓度在各组间无差异。上述结果提示,添加GABA可增强奶牛抗氧化能力,改善奶牛健康状况,可能通过CCK途径提高奶牛采食量。
3.2GABA对采食相关基因表达的影响(试验五)
根据体重选取断奶湖羊24只,按随机区组设计分为3个处理,每个处理4个重复(栏),每个重复2只羔羊。采用全混合日粮模式,在基础日粮上添加0mg/d(对照)、140mg/d和280mg/d的RP-GABA (GABA分别为0,70和140mg/d),试验期为42天,每周连续测定三次日采食量。在饲养试验结束时进行屠宰试验,取十二指肠和回肠粘膜上皮,测定采食相关基因mRNA丰度。结果发现,在日粮中添加140mg/d GABA可显著提高断奶湖羊采食量(P<0.05),并提高试验期4-6周湖羊日增重(P<0.05),显著提高十二指肠上皮GABA-B受体1nRNA丰度,抑制CCK-2受体的相对表达量(P<0.05)。提示在反刍动物中,GABA可能通过CCK途径,对采食量进行调控。
综上所述,包被材料是RP-GABA的稳定性关键因素；在日粮中添加GABA可提高围产期和泌乳盛期荷斯坦奶牛的采食量,进而提高其产奶性能,适宜的添加剂量分别为1.2g/d和0.6g/d。GABA对反刍动物的调控可能与CCK代谢通路有关。
Gama-aminobutyric acid (GABA) is one of the most important neurotransmitter in central nervous system, and has many regulatory functions on the animals. Many researches have been conducted with mono-gastric animals on the effects of GABA. However, there are few reports on ruminant animals. Due to the ruminal degradability of GABA, rumen-protected technology of GABA was developed to make GABA available in ruminants. A kind of rumen-protected (RP-GABA) which is stable in rumen but released efficiently in post-rumen digestive tracts was developed; the selected RP-GABA was then used to determine the effects of RP-GABA on feed intake and milk performance in transition and early lactating cows; finally, mechanisms of GABA on dairy cows were investigated by changes in serum variables and expression of feed intake related genes.
1. Preparation of RP-GABA (Trail1)
As GABA could be easily degraded in rumen, it should be protected before it can be applied in ruminant animals. The trail was conducted to prepare RP-GABA of high rumen-protected rate and intestinal digestive rate. Nine samples were designed and prepared, according to orthogonal design L9(34). GABA content, coating materials and air pressure were defined as the variations of preparation protocol. Dissolution rates were measured and four products with lower dissolution rates were selected to determine the ruminal and post-ruminal dissolution rates. The study was then conducted to estimate the dissolution rates of RP-GABA with the methods of in vitro and in sacco. All products had lower degraded rates than that of unprotected GABA (almost degraded within2h). Post-ruminal dissolution rates of the four products were over90%, indicating that they can be almost dissolved. All products had dissolution rates above90%in the digestive tract and the total digestive rates of were estimated to be from49.2%-75.8%. In summary, within the three factors (coating material, air pressure and GABA content), coating material played the key role in stability of RP-GABA. RP-GABA (50%GABA content, solid palm fatty acid pelled, air pressure11kp) was of low dissolution rate and high post-ruminal dissolution rate, and was selected to be used in all the following in vivo trails.
2. Effects of GABA on feed intake and lactating performance in Holstein dairy cows (Trail2and3)
Transition and early lactating are critical physiological periods for Holstein dairy cows. Feed intake of both transition and early lactating cows may not meet the requirements of the increasing milk yield. Thus, feed intake of these cows is a key issue for dairy nutrition. Thus, prepared RP-GABA was applied to investigate its effects on transition and early lactating cows.
2.1Effects of dietary GABA on feed intake and lactating performance in transition dairy cows (Trail2)
Transition cows:Forty multiparous cows were blocked based on previous milk production, parity, estimated calving date and body weight and were randomly assigned to one of four treatments and received either no GABA (control) or were supplemented with non-protected GABA (1.2g/day) or RP-GABA (1.2and2.4g/day (GABA=0.6and1.2, respectively)), respectively. The experiment lasted from2weeks before calving to4weeks after calving. Milk yield and milk composition were recorded weekly. The results showed that, during3rd and4th week, cows fed1.2g/d GABA had higher feed intake, and higher milk protein yield (4th week), compared with that of the control.
2.2Effects of dietary GABA on feed intake and lactation performance in early lactating dairy cows (Trail3)
Forty-eight multiparous cows were blocked based on days in milk (DIM), milk production and parity and were randomly assigned to one of four treatments with RP-GABA added at levels of0,0.8,1.6or2.4g/d (GABA=0,0.4,0.8, and1.2, respectively), respectively. The experimental period was8weeks. Milk yield and milk composition (fat, true protein, lactose) were recorded weekly. Results indicated that cows fed GABA consumed more grass hay (P<0.05). Cows consumed0.4g/d GABA were of higher milk yield (P<0.05), compared those of the control, but yielding off when cows consumed1.2g/d RP-GABA. Milk protein yield increased in the cows fed0.4or0.8g/d RP-GABA, respectively. No difference was observed in either fat or protein contents of milk. Cows fed0.4and0.8g/d GABA had higher lactose contents, compared with those of the control (P<0.05). In summary, dry matter intake and milk performance could enhanced dose-dependently in cows fed GABA.
In summary, GABA enhanced milk performance by increasing feed intake in Holstein dairy cows.
3The mechanism of GABA on dry matter intake in dairy cows (Trail4and5)
In mono-gastric animals, GABA mainly regulated feed intake through neuropeptide Y (NPY) and cholecystokinin (CCK) pathways. However, the mechanism is not clear in dairy cows. Thus, the current study was conducted to investigate the mechanism of GABA in feed intake regulation in dairy cows, by determining serum variables and genes expression related with feed intake (with Hu sheep as model).
3.1Effects of GABA on serum variables in dairy cows (Trail4)
In trail2, sera of transition cows were collected weekly. Serum contents of NPY, CCK, leptin and biochemical and antioxidative metabolites were analyzed weekly and the calving day. In trail3, sera of early lactating cows were collected in the1st,4th, and7th week, and serum contents of GABA, neuropeptide Y, and biochemical and antioxidant variables were analyzed. The results indicated that feeding1.2g/d GABA enhanced serum SOD (super oxide dismutase), GSH-Px (gluthathione peroxidase) and T-AOC (total antioxidation capacity) contents, decreased serum NEFA contents, and decreased serum CCK contents during3-4week after calving, compared with that of the control (P<0.05). No difference was observed in leptin among all treatments. For early lactating cows, animals fed0.8g/d GABA had higher GSH-Px and lower malondialdehyde (MDA) contents in sera, compared with those of the control (P<0.05). All cows fed GABA were of low NEFA contents (P<0.05). GABA did not change serum NPY contents in both studies. In summary, GABA enhanced anti-oxidative capacity and health condition. GABA enhanced feed intake through pathway related with CCK.
3.2Effect of GABA on gene expression related with feed intake (Trail5)
Twenty-four Hu lambs weaned at age of50d were divided into three groups of eight lambs each, with four units of two lambs in each group, based on body weight, and were randomly assigned to three dietary treatments with addition of RP-GABA at levels of0,140or280mg/d (GABA=0,70,140mg/d). Feeding trial lasted6weeks. The DMI was recorded weekly in three consecutive days. At the end of the trial, four lambs from each group were slaughtered, and duodenum and ileum mucosa were obtained from RNA abundance measurements of genes regulating feed intake. The result indicated that DMI was significantly higher (P<0.05) in the lambs fed140mg/d GABA than those of the control during the whole period. Compared with control, lambs fed140mg/d RP-GABA had higher mRNA abundance of GABA-B receptor (P<0.05) and lower mRNA abundance of CCK-2receptor (P<0.05) in duodenum mucosa. The results indicated that RP-GABA regulated dry matter intake by affecting mRNA abundances of GABA-B and CCK-2receptors in duodenum epithelia.
In summary, coating material could be the key factor in stability of the RP-GABA products. Addition of GABA enhanced feed intake and then milk performance in both transition and early lactating cows, respectively. The optimal doses of GABA were1.2and0.6g/d for transition cow and early lactating cows, respectively. Regulatory effect in feed intake induced by GABA might be related with CCK metabolic pathway.
引文
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