动物营养学报    2022, Vol. 34 Issue (10): 6514-6526    PDF    
发酵罗汉果渣对黄羽肉鸡生长性能、血清生化指标和肉品质的影响
梁丽芬1 , 孙涛1 , 李铁军2 , 宾石玉1 , 侯振平3     
1. 广西师范大学生命科学学院,珍稀濒危动植物生态与环境保护教育部重点实验室,桂林 541006;
2. 中国科学院亚热带农业生态研究所,长沙 410125;
3. 中国农业科学院麻类研究所,长沙 410205
摘要: 本试验旨在探究饲粮中添加发酵罗汉果渣等量替代玉米对中速型黄羽肉鸡生长性能、血清生化指标和肉品质的影响。先采用强饲代谢试验测定黄羽肉鸡对发酵罗汉果渣的营养物质表观代谢率,再选用360只1日龄中速型黄羽肉鸡[平均体重(31.03±0.27) g]进行饲养试验,随机分为4个组,每组6个重复,每个重复15只。对照组饲喂玉米-豆粕型基础饲粮,1~21日龄,基础饲粮中发酵罗汉果渣替代玉米水平分别为0(对照组)、1%(试验Ⅰ组)、3%(试验Ⅱ组)、5%(试验Ⅲ组);22~42日龄和43~70日龄,基础饲粮中发酵罗汉果渣替代玉米水平分别为0(对照组)、5%(试验Ⅰ组)、8%(试验Ⅱ组)、10%(试验Ⅲ组)。试验期为70 d。结果表明:1)黄羽肉鸡对发酵罗汉果渣营养物质表观代谢率分别为粗蛋白质72.96%、粗灰分83.88%、粗脂肪72.90%、粗纤维83.58%、总能87.44%。2)饲粮中添加发酵罗汉果渣等量替代玉米对中速型黄羽肉鸡的平均日采食量、平均日增重以及料重比均无显著影响(P>0.05)。3)与对照组相比,试验Ⅲ组的血清总蛋白含量显著降低(P < 0.05);试验Ⅰ、Ⅱ和Ⅲ组的血清尿素氮含量显著降低(P < 0.05),试验Ⅰ和Ⅱ组的血清低密度脂蛋白胆固醇含量显著降低(P < 0.05)。血清低密度脂蛋白胆固醇含量随饲粮中发酵罗汉果渣添加水平增加呈先降低后升高的二次曲线关系(P < 0.05),通过回归分析,当饲粮中发酵罗汉果渣添加水平为5.91%时,血清低密度脂蛋白胆固醇含量最低。4)与对照组相比,试验Ⅰ、Ⅱ组和Ⅲ组的胸肌45 min红度值显著提高(P < 0.05),试验Ⅱ组的腿肌蒸煮损失显著降低(P < 0.05)。腿肌蒸煮损失随着发酵罗汉果渣添加水平的增加呈先降低后升高的二次曲线关系(P < 0.05),通过回归分析,当饲粮中罗汉果渣添加水平为6.66%时,腿肌蒸煮损失最低。综上所述,饲粮中添加发酵罗汉果渣等量替代玉米可降低血清尿素氮含量和腿肌蒸煮损失,提高胸肌红度值,从而改善中速型黄羽肉鸡血清生化指标和肉品质。综合试验结果,建议在中速型黄羽肉鸡饲粮中发酵罗汉果渣适宜添加水平为5.91%~6.66%。
关键词: 发酵罗汉果渣    黄羽肉鸡    生长性能    血清生化指标    肉品质    
Effects of Fermented Siraitia grosvenorii Residue on Growth Performance, Serum Biochemical Indexes and Meat Quality of Yellow-Feathered Broilers
LIANG Lifen1 , SUN Tao1 , LI Tiejun2 , BIN Shiyu1 , HOU Zhenping3     
1. Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection, Ministry of Education, College of Life Science, Guangxi Normal University, Guilin 541006, China;
2. Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China;
3. Institute of Bast Fiber Crops, Chinese Academy of AgricuItureal, Changsha 410205, China
Abstract: The purpose of this experiment was to explore the effects of dietary fermented Siraitia grosvenorii residue equivalent instead of corn on growth performance, serum biochemical indexes and meat quality of medium speed yellow-feathered broilers. Firstly, the apparent metabolic rates of nutrients in fermented Siraitia grosvenorii residue was determined by strong feeding metabolic test; then, a total of 360 one-day-old medium-speed yellow-feathered broilers [(average body weight of (31.03±0.27) g] were randomly divided into 4 groups with 6 replicates in each group and 15 broilers in each group. Broilers in the control group were fed a corn-soybean meal basal diet, during 1 to 21 days of age, the levels of fermented Siraitia grosvenorii residue instead of corn in the basic diet were 0 (control group), 1% (test group Ⅰ), 3% (test group Ⅱ) and 5% (test group Ⅲ), respectively; during 22 to 42 days of age and 43 to 70 days of age, the levels of fermented Siraitia grosvenorii residue instead of corn in the basic diet were 0 (control group), 5% (test group Ⅰ), 8% (test group Ⅱ) and 10% (test group Ⅲ), respectively. The experimental period was 70 days. The results showed as follows: 1) the apparent metabolic rates of nutrients in fermented Siraitia grosvenorii residue of yellow feather broilers were as follows: crude protein 72.96%, ash 83.88%, ether extract 72.90%, crude fiber 83.58%, gross energy 87.44%. 2) Dietary fermented Siraitia grosvenorii residue equivalent instead of corn had no significant effects on average daily feed intake, average daily gain and feed to gain ratio of medium speed yellow-feathered broilers (P>0.05). 3) Compared with the control group, the serum total protein content of group Ⅲ was significantly decreased (P < 0.05), the serum urea nitrogen of groups Ⅰ, Ⅱ and Ⅲ was significantly decreased (P < 0.05), and the serum low density lipoprotein cholesterol content of groups Ⅰ and Ⅱ was significantly decreased (P < 0.05). The serum low density lipoprotein cholesterol content showed a firstly decreased and then increased quadratic relationship with the dietary fermented Siraitia grosvenorii residue supplemental level increased (P < 0.05), through regression analysis, when the dietary fermented Siraitia grosvenorii residue supplemental level was 5.91%, the serum low density lipoprotein cholesterol content was the lowest. 4) Compared with the control group, the breast muscle 45 min redness value of groups Ⅰ, Ⅱ and Ⅲ was significantly increased (P < 0.05), and the leg muscle cooking loss of group Ⅱ was significantly decreased (P < 0.05). The leg muscle cooking loss showed a firstly decreased and then increased quadratic relationship with the dietary fermented Siraitia grosvenorii residue supplemental level increased (P < 0.05), through regression analysis, when the dietary fermented Siraitia grosvenorii residue supplemental level was 6.66%, the leg muscle cooking loss was the lowest. To sum up, dietary fermented Siraitia grosvenorii residue equivalent instead of corn can reduce the serum urea nitrogen content and leg muscle cooking loss, increase the breast muscle redness value, thus improve the serum biochemical indexes and meat quality of medium speed yellow-feathered broilers. It is suggested that the dietary fermented Siraitia grosvenorii residue suitable supplemental level of medium-speed yellow-feathered broilers is 5.91% to 6.66%.
Key words: fermented Siraitia grosvenorii residue    yellow-feathered broilers    growth performance    serum biochemical indexes    meat quality    

目前我国饲料原料的国际依赖度已经达到较高的水平,饲料原料匮乏已成为限制我国畜禽养殖业发展的瓶颈。因此,农业农村部《饲料中玉米豆粕减量替代工作方案》(2021年3月)表明,当前玉米、豆粕减量替代迫在眉睫。近年发现,利用生物发酵技术对非常规饲料进行处理,既能深化非常规原料的加工,又能通过增加其自身的营养价值来促进地源饲料的开发,使作物副产品得到最大程度地利用,从而减少饲料成本,增加养殖户的收入[1]。大量研究表明,非常规饲料经发酵后,通过增加粗蛋白质和有机物含量[2]、减少抗营养因子含量来改善饲料营养品质[3-4],同时还通过提供益生菌、消化酶以及其他代谢产物来提高畜禽吸收消化能力[5],促进畜禽生长[6],改善肉品质[7]

罗汉果(Siraitia grosvenorii)是一种多年生藤本植物果实,以广西分布最多,且产量占全球80%以上。据统计,每年用于生产罗汉果甜苷的罗汉果数量过亿,提取后剩余的残渣为罗汉果渣,然而大部分罗汉果渣遭到废弃,造成资源的严重浪费[8]。罗汉果渣中含有丰富的黄酮、罗汉果苷、多糖等活性成分,是一种附加值较高的功能性原料,具有较高的饲料原料开发潜力与应用价值。罗汉果渣可作为非常规饲料原料进行开发利用。王启芝等[9]研究认为,罗汉果渣的常规营养成分中粗蛋白质含量为8.94%,总能为13.43 MJ/kg,可以作为一种非常规饲料资源进行开发。也有研究表明,罗汉果渣的营养价值较低,不能直接用作优质饲料来源,但可以采取适当的处理来减少其纤维含量,提高营养物质消化率[10]。罗汉果渣中存在果胶、单宁以及粗纤维等抗营养因子,阻碍其饲料化利用[11],而菌酶协同发酵可分解农副产物中的抗营养因子[12]。因此,将罗汉果渣发酵后用于畜禽饲料中是切实可行的,并且具有广阔的应用前景,而当前有关发酵罗汉果渣的饲用营养价值,特别是对家禽生长性能、血清生化指标和肉品质的研究数据较为缺乏。因此,本试验以罗汉果渣为原料,探究饲粮中发酵罗汉果渣等量替代玉米对黄羽肉鸡生长性能、血清生化指标和肉品质的影响,探讨在肉鸡饲粮中发酵罗汉果渣的适宜添加水平,为发酵罗汉果渣在黄羽肉鸡生产应用中提供参考。

1 材料与方法 1.1 试验材料

发酵罗汉果渣由某生物科技有限公司提供,主要由罗汉果渣和麸皮以4∶1的比例混合,经酶制剂(木聚糖酶、葡聚糖酶、酸性蛋白酶以及碱性蛋白酶)和菌种(酵母菌、芽孢杆菌以及乳酸菌)协同发酵而得,其主要营养成分实测值分别为:粗蛋白质含量10.75%,粗灰分含量4.25%,粗脂肪含量1.63%,粗纤维含量38.18%,总能20.80 MJ/kg;氨基酸含量分别为:蛋氨酸0.12%、苏氨酸0.71%、赖氨酸0.33%、异亮氨酸0.36%、亮氨酸0.69%、苯丙氨酸0.44%、缬氨酸0.46%、天冬氨酸1.12%、丝氨酸0.64%、谷氨酸1.12%、甘氨酸0.64%、丙氨酸0.58%、酪氨酸0.33%、组氨酸0.18%、精氨酸0.39%、脯氨酸0.54%。

1.2 试验设计 1.2.1 代谢试验

选取同一批中速型成年黄羽肉鸡5只,单笼单只饲养。预试期3 d后,将所有试验鸡禁食48 h,禁食结束后,每只试验鸡强饲50 g混有二氧化钛的饲粮,自由饮水并收集48 h排泄产物,把粪盘上的皮屑、羽毛以及饲料颗粒等清理干净,将所有的粪便转移到已知重量的铝盒中,称重,粪样与10%的盐酸混合均匀(防止氮的损失)。将粪便样品放于65 ℃烘箱中烘干至恒重,粉碎粪样,过40目筛后装入自封袋保存,待测常规营养成分。

1.2.2 饲养试验

选用360只健康的1日龄中速型黄羽肉鸡,平均体重为(31.03±0.27) g,随机分为4个组,每组6个重复,每个重复15只。试验期70 d,分为3个阶段,分别是雏鸡阶段(1~21日龄)、生长阶段(22~42日龄)和育成阶段(43~70日龄)。对照组肉鸡饲喂玉米-豆粕基础饲粮;1~21日龄,在基础饲粮中分别添加1%(试验Ⅰ组)、3%(试验Ⅱ组)和5%(试验Ⅲ组)的发酵罗汉果渣等量替代玉米;22~42日龄和43~70日龄,在基础饲粮中分别添加5%(试验Ⅰ组)、8%(试验Ⅱ组)和10%(试验Ⅲ组)的发酵罗汉果渣等量替代玉米。试验在湖南省益阳市沅江市中国农业科学院麻类研究所石矶湖试验鸡舍内进行,参考GB/T 5916—2020《产蛋鸡和肉鸡配合饲料》配制基础饲粮,其组成及营养水平见表 1,饲喂粉状料,自由饮水。

表 1 基础饲粮组成及营养水平(风干基础) Table 1 Composition and nutrient levels of basal diets (air-dry basis) 
1.3 指标测定 1.3.1 常规营养成分及营养物质表观代谢率

取发酵罗汉果渣和代谢产物(粪样),分别测定粗蛋白质、粗灰分、粗脂肪、粗纤维、总能以及二氧化钛含量,并计算营养物质表观代谢率,计算公式如下:

式中:A1为饲粮中二氧化钛含量(%);A2为粪便中二氧化钛含量(%);F1为饲粮中营养物质含量(%);F2为粪便中营养物质含量(%)。

1.3.2 生长性能

在黄羽肉鸡1、21、42和70日龄,提前12 h禁食后空腹称重,记录肉鸡采食量,计算平均日增重(ADG)、平均日采食量(ADFI)和料重比(F/G),计算公式如下

1.3.3 血清生化指标

在黄羽肉鸡70日龄时,每重复采集1只鸡的血液样本,收集到真空血管中。常温静置约45 min后,在3 000 r/min下离心10 min(4 ℃条件),将血清转移到单独的管中,-20 ℃保存,采用全自动生化分析仪(Cobas C311,瑞士)和试剂盒(北京利德曼生物技术有限公司)测定以下血清生化指标:总蛋白(total protein,TP)、白蛋白(albumin,ALB)、尿素氮(urea nitrogen,UN)、谷丙转氨酶(glutamic-pyruvic transaminase,ALT)、碱性磷酸酶(alkaline phosphatase,ALP)、谷草转氨酶(glutamic oxalacetic transaminase,AST)、葡萄糖(blood glucose,GLU)、总胆固醇(total cholesterol,TC)、甘油三酯(triglyceride,TG)、高密度脂蛋白胆固醇(high density lipoprotein,HDL-C)、低密度脂蛋白胆固醇(low density lipoprotein,LDL-C)、免疫球蛋白G(immunoglobulin G,IgG)、免疫球蛋白M(immunoglobulin M,IgM)。

1.3.4 肉品质

在黄羽肉鸡70日龄时,每重复统一取左半边腿肌、胸肌来测定肉品质,测定指标包括pH、肉色、滴水损失、蒸煮损失和剪切力。

pH:使用胴体pH直测仪(pH-STAR,Matthaus公司,德国)测定胸肌和腿肌的pH(45 min和24 h),每个肉样测定3次。

肉色:使用色差计(CR-410,Minolta公司,日本)测定胸肌、腿肌(45 min和24 h)的亮度(L*)、红度(a*)和黄度(b*)值,每个肉样测定3次。

滴水损失:从每个胸肌、腿肌上的肌肉取大小一致的肉样称重(m1),用铁丝的一端钩住肉样,另一端钩住塑料杯底部,使其悬挂在杯中,悬挂24 h后(4 ℃条件),用纸将肉块表面的水分拭除干净后称重(m2),计算胸肌和腿肌的滴水损失,计算公式如下:

蒸煮损失:每重复取1块肉鸡的胸肌和腿肌,使用电子天平进行称重并记录数值后(m3),用锡箔纸包好,在水浴中煮15 min后取出,冷却至室温,将肉样纸除去表面水分,称重(m4),计算肉鸡胸肌和腿肌的蒸煮损失,计算公式如下:

剪切力:蒸煮损失测定结束,将胸肌、腿肌切成大小和厚度相同的3块肉样,垂直于肌纤维轴放于C-LM3型数显肌肉嫩度仪上进行剪切,并记录数值。

1.4 数据统计分析

采用SPSS 23.0软件对数据进行单因素方差分析(one-way ANOVA),采用Duncan氏法进行多重比较,并进行线性和二次曲线回归分析,结果用平均值±标准差表示,显著水平为P < 0.05。

2 结果 2.1 发酵罗汉果渣营养物质表观代谢率

表 2可知,黄羽肉鸡对发酵罗汉果渣的粗蛋白质和粗脂肪表观代谢率较低,分别为72.96%和72.90%;对粗灰分、粗纤维和总能表观代谢率较高,分别为83.88%、83.58%和87.44%。

表 2 发酵罗汉果渣营养物质表观代谢率 Table 2 Apparent metabolism rates of nutrients of fermented Siraitia grosvenorii residue 
2.2 发酵罗汉果渣对黄羽肉鸡生长性能的影响

表 3可知,与对照组相比,试验Ⅰ组、试验Ⅱ组和试验Ⅲ组3个阶段(1~21日龄、22~42日龄和43~70日龄)ADFI、ADG和F/G均无显著差异(P>0.05)。试验Ⅱ组ADG在各个阶段均为最高。

表 3 发酵罗汉果渣对黄羽肉鸡生长性能的影响 Table 3 Effects of fermented Siraitia grosvenorii residue on growth performance of yellow-feathered broilers
2.3 发酵罗汉果渣对黄羽肉鸡血清生化指标的影响

表 4可知,与对照组相比,试验Ⅲ组血清TP含量显著降低(P < 0.05),降低了18.57%,且血清TP含量随饲粮中发酵罗汉果渣添加水平的增加呈线性关系(P < 0.05)。与对照组相比,试验Ⅰ、Ⅱ和Ⅲ组血清UN含量显著降低(P < 0.05),分别降低了57.58%、39.39%和54.55%,且血清UN含量随饲粮中发酵罗汉果渣添加水平的增加呈线性关系(P < 0.05)。与对照组相比,试验Ⅰ、Ⅱ组血清LDL-C含量显著降低(P < 0.05),分别降低了36.36%和33.88%,且血清LDL-C含量随饲粮中发酵罗汉果渣添加水平增加呈先降低后升高的二次曲线关系(P < 0.05),通过回归分析,二次曲线模型方程式为:y=0.013 2x2-0.155 9x+1.206 4,依此模型计算,当饲粮中发酵罗汉果渣添加水平为5.91%时,血清LDL-C含量最低。各组之间血清ALP、ALT、AST活性以及ALB、GLU、TG、TC、HDL-C、IgG和IgM含量均无显著差异(P>0.05)。

表 4 发酵罗汉果渣对黄羽肉鸡血清生化指标的影响 Table 4 Effects of fermented Siraitia grosvenorii residue on serum biochemical indices of yellow-feathered broilers
2.4 发酵罗汉果渣对黄羽肉鸡肉品质的影响

表 5可知,与对照组相比,试验Ⅰ、Ⅱ、Ⅲ组胸肌45 min a*值显著提高(P < 0.05),分别提高了49.33%、53.45%和57.94%,且胸肌45 min a*值随饲粮中发酵罗汉果渣添加水平增加呈线性关系(P < 0.05)。试验Ⅰ、Ⅱ、Ⅲ组胸肌剪切力与对照组相比无显著差异(P>0.05);但与试验Ⅱ、Ⅲ组相比,试验Ⅰ组胸肌剪切力显著降低(P < 0.05)。与对照组相比,试验Ⅱ组腿肌蒸煮损失显著降低(P < 0.05),降低了13.25%;试验Ⅰ、Ⅲ组无显著差异(P>0.05),但也分别降低了7.44%、5.95%;腿肌蒸煮损失随着发酵罗汉果渣添加水平的增加呈现先降低后升高的二次曲线关系(P < 0.05),通过回归分析,二次曲线模型方程式为:y=0.105 0x2-1.398 1x+43.736 5,根据此模型计算,当饲粮中罗汉果渣添加水平为6.66%时,腿肌蒸煮损失最低。

表 5 发酵罗汉果渣对黄羽肉鸡肉品质的影响 Table 5 Effects of fermented Siraitia grosvenorii residue on meat quality of yellow-feathered broilers
3 讨论 3.1 黄羽肉鸡对发酵罗汉果渣的营养物质表观代谢率

菌酶协同发酵能高效降解饲料原料,改善饲料品质,促进动物消化吸收,进而提高利用率[13-14]。通过代谢试验发现,黄羽肉鸡除了对发酵罗汉果渣中粗蛋白质和粗脂肪表观代谢率相对较低外,对其他营养物质表观代谢率均较高,这与陈小连等[15]的研究结果相似。罗汉果渣是罗汉果加工产品后的副产物,因其富含多种活性成分且营养价值高,可作为一种非常规饲料原料,经发酵后可替代饲粮中部分常规饲料,减少饲料成本,从而获得可观的经济效益,同时对缓解饲料原料短缺具有重要的现实意义。

3.2 发酵罗汉果渣对黄羽肉鸡生长性能的影响

生长性能是评价发酵饲料营养状况及经济效益的重要指标[16]。大量研究表明,发酵饲料不仅能提高营养价值,而且通过改善其适口性促进动物采食,在改善畜禽生长性能方面具有重要作用[17-18]。这是由于发酵中添加的菌种不仅能改善动物肠道菌群,且在代谢过程中产生多种营养物质(如氨基酸、蛋白质和有机酸等),改善饲料品质[19-20];同时还可激活淀粉酶、蛋白酶等与碳水化合物和蛋白质代谢相关的消化酶,加快畜禽消化吸收,进而提高生长性能[21]。本试验发现,饲粮中发酵罗汉果渣等量替代玉米对黄羽肉鸡的ADFI、ADG以及F/G均无显著影响,表明饲粮中发酵罗汉果渣等量替代玉米对黄羽肉鸡的生长性能无不良影响,这与Guo等[22]、Gao等[23]、Niu等[24]的研究结果类似。推测未能提高黄羽肉鸡生长性能有以下2方面原因,一方面可能是由于基础饲粮中的营养物质已满足黄羽肉鸡的生长需求,因此各组之间的ADFI均无显著差异,进一步导致各组之间的F/G差异也不显著;另一方面可能与发酵饲料主要原料的组成有关,由于罗汉果渣中存在较高水平的抗营养因子,经发酵后仍使黄羽肉鸡对其消化率及利用率不够明显,从而未能很好地提高黄羽肉鸡的生长性能[25]。另外,本试验结果发现,与试验Ⅰ、Ⅲ组相比,试验Ⅱ组的ADG最高,效果较好,表明饲粮中发酵罗汉果渣的添加水平与黄羽肉鸡的生长性能并非呈正相关,而是需要添加适宜水平才能达到最大化的饲料利用率。推测其原因可能是发酵饲料中含有较多的益生菌,而不足或过量添加都会影响肠道菌群结构,进而影响宿主对饲粮中的营养物质消化吸收及生长发育[26]。综上所述,在玉米-豆粕型基础饲粮中雏鸡阶段添加3%发酵罗汉果渣,在生长和育成阶段添加8%发酵罗汉果渣等量替代玉米效果最佳,不但对黄羽肉鸡的生长性能无不良影响,且能降低饲料成本,增加养殖户收益。

3.3 发酵罗汉果渣对黄羽肉鸡血清生化指标的影响

血清生化指标是反映机体营养代谢功能和健康状况的重要指标[27]。TP主要反映体内蛋白质吸收状况[28]。本试验结果显示,与对照组相比,试验Ⅲ组血清TP含量显著降低,降低了18.57%,而试验Ⅰ、Ⅱ组没有显著差异,说明添加适量的发酵罗汉果渣不影响黄羽肉鸡对蛋白质的吸收和代谢,但过量添加会影响机体对蛋白质的吸收,可能是发酵罗汉果渣中的抗营养因子未被完全降解,从而阻碍了肉鸡机体对发酵料中蛋白质的分解与利用[29]。血清UN是动物体内蛋白质代谢的终产物,可反映机体蛋白质代谢和饲粮氨基酸平衡状况,当氨基酸平衡良好时,血清UN含量降低[30-31]。本试验中,试验Ⅰ、Ⅱ和Ⅲ组血清UN含量较对照组显著降低,与Xu等[32]的研究结果相似。血清UN含量降低的原因可能是发酵罗汉果渣中存在益生菌,其通过利用氨基酸脱氨基反应生成的氨气(NH3)来合成菌体蛋白,减少进入肝中的NH3数量,阻碍UN的形成,从而使血清UN含量显著降低[33]。LDL-C、HDL-C、TG以及TC是反映脂肪代谢的关键指标,能够衡量畜禽饮食均衡情况[34]。在本试验中,与对照组相比,试验Ⅰ、Ⅱ和Ⅲ组的血清TG、TC以及HDL-C含量均无显著差异,但血清LDL-C含量显著降低,与Ashayerizadeh等[35]的研究结果一致。血清LDL-C含量降低可能是发酵罗汉果渣中的甜苷抑制黄羽肉鸡体内的LDL-C合成,进而调控脂类代谢[36]。综上所述,饲粮中发酵罗汉果渣等量替代玉米可使黄羽肉鸡血清UN和LDL-C含量降低,从而改善血清生化指标,促进肉鸡机体健康。

3.4 发酵罗汉果渣对黄羽肉鸡肉品质的影响

肉品质是畜禽生产中的一个关键要素,通常用pH、肉色、剪切力、滴水损失以及蒸煮损失等指标来反映肉品质[37]。pH是用来评定感官品质的指标之一,pH的高低将会直接影响肌肉的肉色和嫩度,动物被屠宰后其血液循环的营养供应被中断,引起糖酵解反应,进而产生乳酸,从而降低肌肉中的pH[38-39]。本试验发现,与对照组相比,试验Ⅰ、Ⅱ和Ⅲ组pH无显著差异。肉色是消费者做出购买决策的决定性因素之一,反映肉色的指标有L*、a*和b*。L*值越高表明肌肉水分渗出高,越容易形成PSE肉。一般情况下,a*值越高且b*值越低则表明肉的感官品质越好[40]。本试验发现,与对照组相比,试验Ⅰ、Ⅱ和Ⅲ组的45 min胸肌a*值均显著提高,表明发酵罗汉果渣的添加可增加肌肉亮度和色泽来改善肉色,这与孙波等[41]研究结果相类似。肉色得到改善的原因可能是罗汉果渣中的罗汉果多糖、黄酮具有抗氧化功能,能够阻碍细胞膜脂质发生氧化反应,进而可通过延缓肌红蛋白被氧化的速度来提高亮度[42]。蒸煮损失是评价肌肉质量的重要指标之一,能反映肌肉的持水能力[43]。本试验发现,与对照组相比,试验Ⅱ组腿肌蒸煮损失显著降低,降低了13.25%。这可能是发酵罗汉果渣中含有的活性物质可有效地减少屠宰后的肌肉细胞被自由基等有害物质损害,同时延缓其氧化,从而降低细胞中的水分损失,提高系水能力[44-45]。嫩度是反映消费者对肌肉口感是否满意的一个重要指标,可直接对肉的商品价值和食用价值产生影响,通常用剪切力来衡量肌肉的嫩度[46]。本试验中,与对照组相比,试验Ⅰ、Ⅱ和Ⅲ组剪切力均差异不显著。综上所述,饲粮中添加发酵罗汉果渣等量替代玉米可使黄羽肉鸡的肉品质得到改善。

4 结论

饲粮中添加发酵罗汉果渣等量替代玉米对中速型黄羽肉鸡的生长性能无不良影响,但能改善血清生化指标和肉品质。综合各指标效果考虑,本试验条件下,以雏鸡阶段饲粮中添加3%发酵罗汉果渣、生长和育成阶段饲粮中添加8%发酵罗汉果渣等量替代玉米生产效应最佳,根据血清生化和肉品质指标的回归分析结果,建议在中速型黄羽肉鸡饲粮中发酵罗汉果渣适宜添加水平为5.91%~6.66%。

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