动物营养学报    2021, Vol. 33 Issue (3): 1418-1429    PDF    
饲粮中添加共轭亚油酸和铬对热应激肉鸡生长性能、胴体性能、肉品质及脂肪沉积的影响
徐蔼宣 , 杨建 , 陈志勇 , 张正帆 , 黄艳玲     
西南民族大学生命科学与技术学院, 动物科学国家民委重点实验室, 成都 610041
摘要: 本试验旨在研究饲粮中添加共轭亚油酸(CLA)和铬(丙酸铬)对热应激肉鸡生长性能、胴体性能、肉品质及脂肪沉积的影响。试验采用2×3两因素随机试验设计,设置2个CLA水平(0、1%)和3个铬水平(0、0.2、0.4 mg/kg)。选用216只1日龄科宝(Cobb)500白羽雌雏肉鸡,随机分为6个组,每组6个重复,每个重复6只鸡。环境温度保持在32~34℃,每周末进行1次肉鸡体温(肛温)的测定,以确保其处于热应激状态。试验期42 d。结果表明:1)饲粮中添加CLA和铬以及二者互作对热应激肉鸡平均日采食量、平均日增重和料重比均无显著影响(P>0.05)。2)饲粮中添加CLA提高了热应激肉鸡腿肌率(P < 0.05),并有提高屠宰率的趋势(P=0.071),但对胸肌率、全净膛率均无显著影响(P>0.05)。饲粮中添加铬有降低热应激肉鸡胸肌率的趋势(P=0.099)。CLA和铬互作对热应激肉鸡胴体性能没有显著影响(P>0.05)。3)饲粮中添加CLA降低了热应激肉鸡胸肌和腿肌黄度(b*)值和胸肌亮度(L*)值(P < 0.05),对其他肉品质指标无显著影响(P>0.05)。饲粮中添加0.2 mg/kg铬显著提高了热应激肉鸡胸肌pH24 hP < 0.05),饲粮中添加铬对腿肌肉品质指标无显著影响(P>0.05)。CLA和铬互作对热应激肉鸡胸肌和腿肌肉品质指标无显著影响(P>0.05)。4)饲粮中添加CLA显著降低了热应激肉鸡的腹脂率和腿肌肌内脂肪含量(P < 0.05)。饲粮中添加铬有降低热应激肉鸡腹脂率的趋势(P=0.097),但对胸肌和腿肌肌内脂肪含量均无显著影响(P>0.05)。CLA和铬互作有降低热应激肉鸡腹脂率的趋势(P=0.071),其中,1% CLA+0.2 mg/kg铬组合降低腹脂率效果最好。5)饲粮中添加CLA和铬均显著提高了热应激肉鸡肝脏铬含量(P < 0.05),且CLA和铬互作对热应激肉鸡肝脏铬含量有显著影响(P < 0.05)。由此可见,饲粮中添加CLA对热应激肉鸡生长性能无显著影响,但改善了肉鸡的胴体性能并促进了肝脏中铬沉积;饲粮中添加铬对热应激肉鸡生长性能、胴体性能均无显著影响,但提高了胸肌pH24 h,并有降低腹脂率的趋势;CLA和铬互作有降低腹脂率的趋势,以1% CLA+0.2 mg/kg铬组合效果较好。
关键词: 共轭亚油酸        生长性能    胴体性能    肉品质    脂肪沉积    热应激肉仔鸡    
Effects of Conjugated Linoleic Acid and Chromium on Growth Performance, Carcass Performance, Meat Quality and Fat Deposition of Heat-Stressed Broilers
XU Aixuan , YANG Jian , CHEN Zhiyong , ZHANG Zhengfan , HUANG Yanling     
College of Animal Science and Technology, Southwest Minzu University, Key Laboratory of Animal Science of National Civil Affairs Commission, Chengdu 610041, China
Abstract: This experiment was conducted to investigate the effects of conjugated linoleic acid (CLA) and chromium (chromium propionate) on growth performance, carcass performance, meat quality and fat deposition of heat-stressed broilers. A 2×3 two factor randomized experiment design was adopted, and set 2 CLA levels (0 and 1%) and 3 chromium levels (0, 0.2 and 0.4 mg/kg). A total of 216 one-day-old female broiler chicks (Cobb 500) were randomly divided into 6 groups with 6 replicates per group and 6 broilers per replicate. The ambient temperature was maintained at 32 to 34 ℃, and the temperature of broilers (anal temperature) was measured every weekend to ensure that they were in a state of heat stress. The experiment lasted for 42 days. The results showed as follows: 1) dietary CLA and chromium and their interaction had no significant effects on the average daily feed intake, average daily gain and feed to gain ratio of heat-stressed broilers (P>0.05). 2) Dietary CLA significantly increased the leg muscle percentage of heat-stressed broilers (P < 0.05), and had a tendency to increase the dressing percentage (P=0.071), but had no significant effects on the breast muscle percentage and eviscerating percentage (P>0.05). Dietary chromium had a tendency to decrease the breast muscle percentage of heat-stressed broilers (P=0.099). The interaction between CLA and chromium had no significant effects on the carcass performance of heat-stressed broilers (P>0.05). 3) Dietary CLA significantly decreased the yellowness (b*) value in breast muscle and leg muscle and brightness (L*) value in breast muscle of heat-stressed broilers (P < 0.05), but had no significant effects on the other meat quality indexes (P>0.05). Dietary 0.2 mg/kg chromium significantly increased the pH24 h in breast muscle, and dietary chromium had no significant effects on the leg muscle meat quality indexes (P>0.05). The interaction between CLA and chromium had no significant effects on the indexes of meat quality in breast muscle and leg muscle of heat-stressed broilers (P>0.05). 4) Dietary CLA significantly decreased the abdominal fat percentage and leg muscle intramuscular fat content of heat-stressed broilers (P < 0.05). Dietary chromium had a tendency to decrease the abdominal fat percentage of heat-stressed broilers (P=0.097), but had no significant effects on the contents of intramuscular fat in breast muscle and leg muscle (P>0.05). The interaction between CLA and chromium had a tendency to decrease the abdominal fat percentage of heat-stressed broilers (P=0.071), among them, 1% CLA+0.2 mg/kg chromium combination had the best effect. 5) Dietary CLA and chromium significantly increased the liver chromium content of heat-stressed broilers (P < 0.05). The interaction between CLA and chromium had significant effects on the liver chromium content of heat-stressed broilers (P < 0.05). In conclusion, dietary CLA have no significant effects on the growth performance of heat-stressed broilers, but improve the carcass performance and promote the deposition of chromium in live; dietary chromium have no significant effects on the growth performance and carcass performance of heat-stressed broilers, but increase the pH24 h in breast muscle, and tend to reduce the abdominal fat percentage; the interaction between CLA and chromium tend to reduce the abdominal fat percentage, and 1% CLA+0.2 mg/kg chromium combination has the best effect.
Key words: conjugated linoleic acid    chromium    growth performance    carcass performance    meat quality    fat deposition    heat-stressed broilers    

肉鸡被毛厚、无汗腺且代谢旺盛,在全球变暖的大环境下,肉鸡在夏季高密度饲养环境下易受高温的影响产生热应激。热应激会导致肉鸡生长抑制[1]、腹脂沉积增多[2]、肉品质下降[3]、机体免疫力降低[1, 4]等,而家禽肉品质及脂肪的沉积受饲粮因素的影响[5]。通过营养手段有效缓解家禽热应激,降低腹脂沉积,改善肉品质,已成为肉鸡养殖业亟待解决的问题之一。铬是葡萄糖耐量因子(glucose tolerance factor,GTF)的重要组成成分,可以缓解热应激,提高热应激肉鸡生长性能,改善肉品质,降低腹脂沉积[6]。丙酸铬(chromium propionate,CrPro)作为一种新型铬源,是目前美国食品及药品管理局(FDA)唯一允许在家禽饲粮中添加的铬源[7]。共轭亚油酸(conjugated linoleic acids, CLA)是一类含有共轭双键的亚油酸混合物,可以通过调节多种核转录因子的表达,影响脂肪酸的摄取和氧化及脂质的合成代谢,进而降低体脂沉积,改善胴体品质[8]。大量研究表明,CLA和铬对于降低动物体脂沉积及改善肉品质都有一定的作用,但目前关于CLA对热应激肉鸡影响的报道较少,且尚未有对两者互作的研究。因此,我们提出本试验假说:热应激肉鸡饲粮中同时添加铬和CLA,对热应激肉鸡的生长性能、胴体性能、肉品质及脂肪沉积可能存在组合效应。为此,本试验通过在肉鸡饲粮中同时添加CLA和铬,来研究二者及其互作对热应激肉鸡生长性能、胴体性能、肉品质及脂肪沉积的影响,探讨CLA和铬之间是否有互作效应,以期为热应激肉鸡养殖提供一定的参考。

1 材料与方法 1.1 试验材料

CLA购于青岛某生物有限公司,纯度80%,实测值为81.04%;CrPro购于珠海某工业有限公司,铬含量0.04%。

1.2 基础饲粮

基础饲粮参照我国《鸡饲养标准》(NY/T 33—2004)和NRC(1994)[9]肉鸡营养需要,配制玉米-豆粕型基础饲粮,基础饲粮组成及营养水平见表 1

表 1 基础饲粮组成及营养水平(干物质基础) Table 1 Composition and nutrient levels of basal diets (DM basis) 
1.3 试验设计与饲养管理

试验采用2×3两因素随机试验设计,设置2个CLA水平(0、1%)和3个铬水平(0、0.2、0.4 mg/kg),选用216只体重一致的健康的1日龄科宝(Cobb)500白羽雌雏肉鸡,随机分为6个组,每组6个重复,每个重复6只鸡。试验饲粮是在基础饲粮的基础上由CLA等量代替葵花籽油,丙酸铬等量替代玉米淀粉。试验期42 d。

试验场地为西南民族大学科研鸡场,饲养管理按《Cobb肉鸡饲养管理手册》进行。试验开始前对鸡舍消毒。3层重叠式笼养,自由采食和饮水。自动化红外灯控温供暖,环境温度保持在32~34 ℃,相对湿度为60%~70%。每周末进行1次肉鸡体温(肛温)的测定,以确保其处于热应激状态。试验结束时,禁食12 h,以重复为单位空腹称重。

1.4 样品采集及指标测定

配制试验饲粮时现场采样,粉碎过200目筛后置于封口样品袋中低温干燥保存,以备分析钙、总磷、粗蛋白质和铬含量。试验第42天,所有鸡只禁食不禁水12 h,于第2天08:00分别称鸡只空腹个体活重,从每个重复中按平均体重选取2只鸡屠宰,取腹脂、胸肌(右侧)和腿肌(右侧)测定腹脂率、胸肌率和腿肌率等指标,然后将部分胸肌和腿肌样品用塑料袋分装置于4 ℃冰箱内,用于测定肌肉pH、肉色、滴水损失、蒸煮损失及剪切力。另取部分左侧胸肌、腿肌及肝脏(左侧)样品置-80 ℃保存,用于测定胸肌和腿肌肌内脂肪含量及肝脏铬含量。然后将鸡拔毛、去头、去脚和去内脏后称重,测其全净膛率(以上采的肌肉样品均称重并计算在内)。

1.4.1 生长性能指标

分别在试验第1天、第21天和第42天以重复为单位称鸡只空腹重,并记录耗料量,试验鸡死亡数量及原因。计算平均日采食量(ADFI)、平均日增重(ADG)和料重比(F/G)。

1.4.2 胴体性能指标

在试验第21天和第42天每个重复选取2只试验鸡于宰杀前禁食(不禁水)半天,然后称活体重。屠宰时,采用颈静脉放血法,计算屠宰率、全净膛率、胸肌率、腿肌率。

1.4.3 肉品质指标 1.4.3.1 胸肌pH及肉色

宰杀之后取胸肌和腿肌放于封口袋中,编号,放入4 ℃冰箱保存24 h,用pH计(OPTO-STAR)检测测定pH(pH24 h)。在测完pH24 h基础上,用色差仪测定胸肌和腿肌肉色的亮度(L*)、红度(a*)和黄度(b*)值。

1.4.3.2 胸肌、腿肌蒸煮损失

参照Huang等[10]方法测定胸肌和腿肌蒸煮损失,将待测样从-20 ℃冰箱取出后,转移到4 ℃冰箱中解冻1 d,剪掉外边脂肪和结缔组织,切成长×宽×厚为3.0 cm×1.5 cm×0.5 cm的长方体块状,称重(m1)并记录,然后把肌肉用封口塑料袋包装,抽去袋内空气,放入80 ℃恒温水浴锅10 min,水浴后放置室温,用滤纸插去肉样表面水分,称重(m2)并记录。计算公式如下:

1.4.3.3 胸肌、腿肌剪切力

将测定蒸煮损失后的鸡肉样品,用TA-XT Plus物性分析仪测定鸡肉嫩度,测定时使切刀垂直肌纤维方向,切割3个点求平均值。

1.4.3.4 脂肪沉积指标

屠宰后立即剥离腹脂,称重。另剥离胸肌、腿肌和左侧肝脏,取约50 g的胸肌、腿肌和整块左侧肝脏,放置于编号的封口袋中,-20 ℃冰箱保存,待测胸肌肌内脂肪和肝脏脂肪含量。

腹脂:包括腹部与肌胃及泄殖腔周围的脂肪。腹脂率指腹脂重占全净膛重的百分比。

胸肌、腿肌肌内脂肪:用索氏提取法测定胸肌和腿肌肌内脂肪含量[11]。取胸肌、腿肌置于105 ℃干燥箱中烘干,称重;将脱脂滤纸在同条件下烘干,然后取1.5 g磨碎样品包在滤纸中,再次烘干,称重;然后将滤纸包放入索氏抽提器进行抽提。

肝脏脂肪:同胸肌、腿肌肌内脂肪测定方法。

1.4.4 肝脏铬含量

将风干肝脏样品经浓优级硝酸(优级纯)在自动控温电热板中湿消化后,在石墨炉原子吸收光谱仪(型号SOLAAR S2,美国热电公司)上测定肝脏铬含量。

1.5 数据统计分析

采用SAS 9.0软件MIXED程序对数据进行两因素方差分析,以P < 0.05为差异显著,以0.05≤P≤0.10表示有差异显著的趋势,在差异显著的基础上采用LSD法对各组间进行多重比较。数据以平均值和均值标准误(standard error of mean, SEM)表示。

2 结果 2.1 饲粮中添加CLA和铬对热应激肉鸡生长性能的影响

表 2可知,饲粮中添加CLA和铬以及二者互作对热应激肉鸡平均日采食量、平均日增重和料重比均无显著影响(P>0.05)。

表 2 饲粮中添加CLA和铬对热应激肉鸡生长性能的影响 Table 2 Effects of dietary CLA and Cr on growth performance of heat-stressed broilers (n=6)
2.2 饲粮中添加CLA和铬对热应激肉鸡胴体性能的影响

表 3可知,饲粮中添加CLA提高了热应激肉鸡腿肌率(P < 0.05),并有提高屠宰率的趋势(P=0.071)。饲粮中添加铬有降低热应激肉鸡胸肌率的趋势(P=0.099)。CLA和铬互作对热应激肉鸡胴体性能没有显著影响(P>0.05)。

表 3 饲粮中添加CLA和铬对热应激肉鸡胴体性能的影响 Table 3 Effects of dietary CLA and Cr on carcass performance of heat-stressed broilers (n=6) 
2.3 饲粮中添加CLA和铬对热应激肉鸡胸肌和腿肌肉品质的影响

表 4表 5可知,饲粮中添加CLA降低了热应激肉鸡胸肌和腿肌肉色b*值和胸肌肉色L*值(P < 0.05),对其他肉品质指标无显著影响(P>0.05)。饲粮中添加0.2 mg/kg铬显著提高了胸肌pH24 h(P < 0.05),饲粮中添加铬对腿肌肉品质指标无显著影响(P>0.05)。CLA和铬互作对热应激肉鸡胸肌和腿肌肉品质指标无显著影响(P>0.05)。

表 4 饲粮中添加CLA和铬对热应激肉鸡胸肌肉品质的影响 Table 4 Effects of dietary CLA and Cr on meat quality of breast muscle of heat-stressed broilers
表 5 饲粮中添加CLA和铬对热应激肉鸡腿肌肉品质的影响 Table 5 Effects of dietary CLA and Cr on meat quality of thigh muscle of heat-stressed broilers
2.4 饲粮中添加CLA和铬对热应激肉鸡脂肪沉积及肝脏铬含量的影响

表 6可知,饲粮中添加CLA显著降低了热应激肉鸡的腹脂率和腿肌肌内脂肪含量(P < 0.05);饲粮中添加铬有降低热应激肉鸡腹脂率的趋势(P=0.097),但对胸肌和腿肌肌内脂肪含量均无显著影响(P>0.05)。CLA和铬互作有降低热应激肉鸡腹脂率的趋势(P=0.071),其中,1% CLA+0.2 mg/kg铬组合降低腹脂率效果最好,较对照组降低了14.55%。饲粮中添加CLA和铬均显著提高了热应激肉鸡肝脏铬含量(P < 0.05),且CLA和铬互作对热应激肉鸡肝脏铬含量有显著影响(P < 0.05)。

表 6 饲粮中添加CLA和铬对热应激肉鸡脂肪沉积及肝脏铬含量的影响 Table 6 Effects of dietary CLA and Cr on fat deposition and liver Cr content of heat-stressed broilers
3 讨论 3.1 饲粮中添加CLA和铬对热应激肉鸡生长性能的影响

目前饲粮添加CLA对动物生长性能影响有改善、抑制及无影响等不同的报道,造成这些差异的原因可能与动物种类、饲粮营养水平以及CLA不同的异构体及添加剂量有关。饲粮中添加0.5%~1.0%的CLA提高了猪的平均日增重,并改善了料重比[12-13]。饲粮中添加超过1%的CLA能抑制肉鸡的生长[14]。Jiang等[15]报道,在肉鸡饲粮中添加1%的CLA对肉鸡生长性能没有显著影响,Du等[16]和Zhang等[17]在肉鸡上的试验也得到了类似的结果。目前关于CLA在热应激肉鸡上的研究较少,与常规饲粮饲喂肉鸡的试验结果类似,本试验结果表明,饲粮中添加1%的CLA对热应激肉鸡的生长性能没有显著影响。

研究表明,饲粮中添加铬能够提高肉鸡的平均日采食量、饲料转化效率,促进肉鸡生长。由于肉鸡对铬的需要量因试验动物阶段、环境以及铬源的不同而存在差异,推荐一般情况下铬添加量为0.2~0.4 mg/kg,应激状态下肉鸡的铬添加量可以提高到0.4~1.2 mg/kg[18]。Hayat等[19]研究发现,在常规饲养状态下,饲粮中添加0.15 mg/kg的CrPro可以提高肉鸡的生产性能。与此相同,Arif等[20]在肉鸡饲粮中添加0、0.2、0.4、0.8、1.6 mg/kg的CrPro,发现在常规饲养状态下,随着CrPro添加水平的增加,饲料转化率和平均日增重显著提高,其中添加0.4 mg/kg的CrPro的肉鸡生长性能最好。Jahanian等[1]研究表明,热应激肉鸡饲粮中添加0.5、1.0 mg/kg蛋氨酸铬极显著提高平均日采食量、均日增重和饲料转化效率。与上述研究结果不同,本试验未观察到饲粮中添加铬对热应激肉鸡生长性能产生影响。Huang等[10]和Xiao等[21]在热应激肉鸡饲粮中添加相同剂量的CrPro,其对生长性能的影响结果与本试验一致。饲粮中添加铬对动物生长性能的影响与试验条件、生长阶段、铬添加水平、基础饲粮铬含量及营养水平等有关。热应激条件下增加了体内铬从尿中的排出,因而提高了动物对铬的需要量[22]。这说明在热应激条件下,需要较高剂量的铬来改善肉鸡的生长性能。本试验结果表明,饲粮中共同添加CLA和铬对热应激肉鸡的生长性能没有互作效应,这可能是由于铬的添加量较少,不足够促进热应激条件下肉鸡的生长。

3.2 饲粮中添加CLA和铬对热应激肉鸡胴体性能的影响

CLA作为一种有效的营养重分配剂,能够促进机体蛋白质的沉积,提高肉鸡肌肉蛋白质含量,还可降低肉鸡脂肪沉积,从而提高瘦肉率[23]。Szymczyk等[24]在肉仔鸡饲粮中添加0、0.5%、1.0%、1.5%的CLA不影响胴体产量、胸肌比例,但显著增加腿肌比例。马建爽等[25]在饲粮中添加0.3%、0.6%、0.9%的CLA,发现添加0.9%的CLA组肉鸡胸肌率和腿肌率显著高于其他各组,而各组肉鸡的屠宰率和全净膛率均无显著差异。目前关于CLA在热应激肉鸡上的研究较少,与常规饲粮饲喂肉鸡的试验结果类似,本试验结果表明,饲粮中添加1%的CLA提高了热应激肉鸡腿肌率,并有提高屠宰率的趋势。

热应激可导致肉鸡矿物质代谢、糖代谢紊乱以及糖原酵解、异生作用加强,葡萄糖利用的加强会导致组织铬动员并排出体外,在热应激条件下,饲粮中添加铬能够改善胴体性能。Toghyani等[22]研究发现,饲粮中添加0.5、1.0和1.5 mg/kg的烟酸铬(chromium polynicotinate,CrNic)和氯化铬(chromium chloride,CrCl3)可以提高热应激肉鸡的胴体率。王刚等[6]研究不同铬源(三氯化铬和吡啶羧酸铬)和铬水平对热应激状态下4周龄爱拔益加肉鸡胴体性能的影响,结果表明,饲粮中添加0.4、10.0、20.0 mg/kg铬均能有效提高肉鸡胸肌率,并且添加10.0 mg/kg铬对腹脂率也有降低效果。与前人研究结果不同,本试验研究表明饲粮中添加不同水平的铬对热应激肉鸡的胴体性能(屠宰率、胸肌率和腿肌率等)并无显著影响。造成结果差异的原因可能是添加的铬源以及剂量不同,以致无法达到预期的效果,具体作用机制尚不清楚。本试验结果显示,饲粮中共同添加CLA和铬对热应激肉鸡的胴体性能没有互作效应。

3.3 饲粮中添加CLA和铬对热应激肉鸡胸肌及腿肌肉品质的影响

CLA可以通过调控脂肪细胞分化、糖脂代谢和肌肉发育(肌纤维类型)来影响肌内脂肪沉积、肌肉发育和肌纤维类型,进而影响脂肪酸组成、肉色、系水力、风味、嫩度和pH等肉的感官品质和营养品质[26]。本研究结果显示,饲粮中添加CLA降低了胸肌L*和b*值以及腿肌b*值,这与前人研究结果一致。Du等[16]给5~8周龄肉鸡添加2%和3%的CLA,其中2%的CLA显著降低了胸肌b*值,但对胸肌L*、a*值、pH没有显著影响。张广民等[27]研究发现,18周龄北京油鸡饲粮中添加1%的CLA能显著降低胸肌b*值,但胸肌L*和a*值、胸肌pH、腿肌pH、胸肌剪切力等没有发生显著变化。CLA影响肉品质可能是通过2种途径:一是作为强抗氧化剂,清除细胞内的过氧化物自由基,保护细胞膜的完整性和稳定性,减少鸡肉表面的渗水,进而降低肌肉表面的反光度[27];二是通过增加肌肉内饱和脂肪酸与不饱和脂肪酸的比例,减少脂质氧化,从而降低肉的b*[28]

目前关于饲粮中添加铬对肉鸡肉品质影响的研究报道比较少,大多研究集中在对猪方面的研究上。Sales等[29]通过已有的数据荟萃分析发现,饲粮中添加铬对猪的肉色、滴水损失、蒸煮损失、剪切力等均没有显著影响。关于铬对肉鸡肉品质的影响,Untea等[30]发现在添加亚麻荠的肉鸡饲粮中加入0.2或0.4 mg/kg的吡啶甲酸铬可以显著提高肌肉的抗氧化性,改善肉品质。本试验结果显示,饲粮中添加铬显著提高了肉鸡胸肌pH24 h,暗示补铬可降低胸肌肌肉氧化酵解,但对其他肉品质没有显著影响。本试验结果与前人研究结果不同,可能与铬的添加水平和形式、作用时间、动物类型和性别、生长阶段、营养状况及环境因素有关。饲粮中同时添加CLA和铬对热应激肉鸡的肉品质没有互作效应。

3.4 饲粮中添加CLA和铬对热应激肉鸡脂肪沉积及肝脏铬含量的影响

与之前大量肉鸡上的研究一致,本试验结果表明饲粮中添加CLA降低了热应激肉鸡腹脂沉积,但目前关于CLA对动物肌内脂肪影响的研究结论不一。猪上的研究表明,饲粮中添加CLA增加了背最长肌肌内脂肪的沉积[31-32]。肉鸡上的研究则不尽相同,柴路等[33]研究表明,饲粮中添加CLA对1~3周龄热应激肉鸡胸肌、腿肌肌内脂肪含量均无显著影响。本试验结果显示,饲粮中添加CLA降低了热应激肉鸡腿肌肌内脂肪含量。

有研究表明,来自于不同铬源的铬均可以降低高温应激环境下肉鸡腹脂的沉积[22],与前人研究结果类似,本试验结果显示饲粮中添加铬有降低热应激肉鸡腹脂率的趋势。饲粮中添加铬对肉鸡肌内脂肪沉积影响的结果不统一。Samanta等[34]在常规饲养肉仔鸡饲粮中添加0.5 mg/kg来自于CrCl3的铬降低了肌肉中脂肪的含量。本试验结果与Huang等[10]研究结果一致,饲粮中铬添加对热应激肉鸡胸肌肌内脂肪含量没有显著影响。本试验研究了饲粮同时添加CLA和铬对肉鸡脂肪沉积的影响,发现CLA和铬互作有降低腹脂率的趋势,其中1% CLA+0.2 mg/kg铬组合降低腹脂率效果较明显,具体作用机理尚待进一步研究。

本试验研究了饲粮铬和CLA的互作效应,结果发现两者共同添加增加了热应激肉鸡肝脏铬含量,从而达到加强铬抑制肉鸡腹脂沉积的效果,这在降低腹脂外在表现中得以验证。Tian等[35]在生长肥育猪的饲粮中添加蛋氨酸铬,研究其对生长肥育猪腹脂中脂肪酸组成的影响,结果表明随着蛋氨酸铬添加剂量的增加,腹脂中CLA含量线性上升,而对其他脂肪酸含量没有显著影响。铬和CLA互作的作用机制还有待进一步研究。

4 结论

① 饲粮中添加CLA对热应激肉鸡生长性能无显著影响,但改善了肉鸡的胴体性能并促进了肝脏中铬沉积。

② 饲粮中添加铬对热应激肉鸡生长性能、胴体性能均无显著影响,但显著提高了胸肌pH24 h,并有降低腹脂率的趋势。

③ CLA和铬的互作有降低腹脂率的趋势,其中以1% CLA+0.2 mg/kg铬组合效果较好。

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