Chinese Journal of Animal Nutrition >

2023 , Vol. 35 >Issue 12: 7714 - 7723

DOI: https://doi.org/10.12418/CJAN2023.701

RESEARCH PAPER

Effects of Low Protein Diet on Performance, Egg Quality, Amino Acid Metabolic Rates and Excretion Parameters of Lohmann Pink Laying Hens during Late Laying Period

  • WANG Jiangshui , 1, 2 ,
  • ZHANG Jiacai 1, 2 ,
  • WANG Yongqiang 1 ,
  • QI Desheng 2 ,
  • GUO Jiyu , 1, *
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  • 1 Guangdong Haid Group Co., Ltd., Guangzhou 511400, China
  • 2 Department of Animal Nutrition and Feed Science, Huazhong Agricultural University, Wuhan 430070, China
* E-mail:

Received date: 2023-06-22

  Online published: 2023-12-11

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Abstract

This experiment was conducted to study the effects of low protein diet on performance, egg quality, amino acid metabolic rates and excretion parameters of Lohmann Pink laying hens during late laying period. A total of 3 024 healthy 61-week-old Lohmann Pink laying hens with similar laying rate were randomly divided into 4 groups with 6 replicates per group and 126 hens per replicate. The control group was formulated with 17.3% crude protein (CP) level in a corn-soybean type diet, and the other three low protein groups were formulated with 16.4% (LCP1 group), 15.3% (LCP2 group) and 13.2% (LCP3 group) CP levels, respectively. All groups had the same levels of lysine (Lys), sulfur-containing amino acid (TSAA) and threonine (Thr) in diets. The experiment lasted for 8 weeks with 1-week adaptation. After the experiment, two hens in each replicate were randomly selected and placed in a metabolic cage, and the metabolic experiment was carried out by total fecal collection method, including a 3-day pre-test period and a 4-day fecal collection period. The results showed as follows: 1) compared with the control group, the laying rate and feed to egg ratio in low protein groups were no significant differences (P<0.05), and the average egg weight was significantly decreased (P<0.05); the daily egg mass and average daily feed intake (ADFI) in LCP3 group were significantly decreased (P<0.05). 2) Compared with the control group, the albumen height, Haugh unit and eggshell strength in low protein groups were no significant differences (P<0.05); the eggshell thickness at week 4 in LCP3 group was significantly increased (P<0.05), but there were no significant differences in eggshell thickness at week 8 among all groups (P>0.05). 3) Compared with the control group, the plasma total protein content in LCP3 group was significantly increased (P<0.05); the plasma contents of albumin (ALB) and globulin (GLB) in low protein groups were no significant differences (P>0.05), and the plasma uric acid (UA) content was significantly decreased (P<0.05). 4) Compared with the control group, the metabolic rates of Lys, methionine (Met) and Thr in LCP1 and LCP2 groups were significantly increased (P<0.05), and the metabolic rates of CP, Lys, Met and Thr in LCP3 group had no significant differences (P>0.05). 5) Compared with the control group, the average daily nitrogen excretion in low protein groups was significantly decreased (P<0.05), and the fecal contents of CP, UA and urea nitrogen (UN) in LCP3 group were significantly decreased (P<0.05). In conclusion, under the premise of balancing dietary levels of Lys, TSAA and Thr levels, dietary CP level decreasing to 15.3% for Lohmann Pink laying hens during the late laying period (62 to 70 weeks of age) has no significant effects on performance and egg quality, but can improve the metabolic rates of CP and AA, and reduce fecal nitrogen excretion.

Key words： low protein diet; laying hens; performance; egg quality; amino acid metabolic rates; excretion parameters

Cite this article

WANG Jiangshui , ZHANG Jiacai , WANG Yongqiang , QI Desheng , GUO Jiyu . Effects of Low Protein Diet on Performance, Egg Quality, Amino Acid Metabolic Rates and Excretion Parameters of Lohmann Pink Laying Hens during Late Laying Period[J]. Chinese Journal of Animal Nutrition, 2023 , 35(12) : 7714 -7723 . DOI: 10.12418/CJAN2023.701

我国畜牧业发展迅速,与此同时也面临着蛋白质饲料资源紧缺和环境污染严重的问题。国家统计局数据显示,2020年我国大豆进口量突破1亿t,而大豆年产量在2022年首次突破2 000万t[1],只占总需求量的18.2%,这意味着我国超80%的大豆需求依赖进口,成为制约畜牧业发展的主要因素之一。绿水青山就是金山银山,随着畜牧业的不断发展,随之而来的环境污染越来越受到人们的关注。《2021年中国生态环境统计年报》[2]显示,农业源(种植业、畜禽养殖业及水产养殖业)总氮排放量为168.5万t,占全国排放量的53.2%。在“蛋白质资源紧缺”和“环境污染严重”两大背景下,低蛋白质饲粮的广泛应用将是必然趋势。
低蛋白质饲粮是指基于理想氨基酸(amino acid,AA)模型,相比营养需要推荐标准降低饲粮粗蛋白质(crude protein,CP)水平2~4个百分点,并通过添加适宜种类和数量的晶体AA,实现蛋白质利用效率最大化的AA平衡饲粮。基于此,饲粮蛋白质的高效利用及生产性能的维稳必然带来饲粮成本的节约和养殖效益的提升,同时降低粪氮排放量,一定程度上减轻畜牧养殖带来的环境污染。近年来,低蛋白质饲粮的应用逐渐成熟,相关研究报道也成为动物营养研究领域的热点。前人研究已多次证实,通过补充晶体AA,低蛋白质饲粮能够维持蛋鸡生产性能和蛋品质稳定[3⇓⇓-6]。Ji等[7]研究发现,21~34周龄海兰W36蛋鸡饲粮CP水平由18%降低至16%对产蛋率、日产蛋量、平均日采食量(average daily feed intake,ADFI)和料蛋比均无显著影响。Torki等[8]报道,52~60周龄来航蛋鸡饲粮CP水平由16.5%降低至12%,对生产性能无显著影响,且提高了抗热应激能力和粪便质量。Keshavarz等[9]研究报道,蛋鸡低蛋白质饲粮(CP水平为13%)补充晶体AA和植酸酶后,其氮排泄量仅为对照组饲粮(CP水平为16.0%~16.5%)的45%,同时对生产性能无显著影响。孟艳莉等[10]研究发现,38~53周龄海兰褐蛋鸡饲粮CP水平降低1个百分点[平衡赖氨酸(lysine,Lys)、蛋氨酸(methionine,Met)、苏氨酸(threonine,Thr)和色氨酸(tryptophan,Trp)],并添加蛋白酶时,对生产性能和蛋品质无负面影响,且能够显著降低粪氮含量,提高蛋白质消化率。然而,关于低蛋白质饲粮对蛋鸡生产性能的影响,前人研究多集中于产蛋高峰期且多从血清生化指标的角度来解析其原因,关于低蛋白质饲粮对产蛋后期养分代谢率的影响鲜有报道。因此,本研究通过代谢试验,测定CP和AA代谢率的变化,分析低蛋白质饲粮对蛋鸡产蛋后期生产性能影响的可能原因,为低蛋白质饲粮在产蛋后期的应用提供理论依据。

1 材料与方法

1.1 试验设计

选取3 024只健康、产蛋率相近的61周龄罗曼粉蛋鸡,随机分为4组,每组6个重复,每个重复126只。采用单因素试验设计,对照组饲粮CP水平设计为17.5%(实测17.3%),3个低蛋白质组饲粮CP水平分别设计为16.5%(实测16.4%,LCP1组)、15.0%(实测15.3%,LCP2组)和13.5%(实测13.2%,LCP3组)。试验采用玉米-豆粕型饲粮,营养水平参照NRC(1994)和NY/T 33—2004《鸡饲养标准》,结合罗曼粉蛋鸡饲养管理手册进行设计,各组饲粮Lys、总含硫氨基酸(total sulfur-containing amino acid,TSAA)和Thr水平均保持一致,饲粮组成及营养水平见表1。预试期1周,正试期8周。正试期结束后每重复随机挑选2只鸡单独放置在代谢笼中,采用全收粪法进行代谢试验,包括3 d预试期和4 d收粪期,每日喂料2次,记录采食量。每日收集粪便,混匀后取50 g加入5 mL 10%的稀盐酸并再次混匀,于-20 ℃冰箱中保存待测。代谢试验结束后,每重复挑选1只鸡,禁食12 h后翅下静脉采血,3 500 r/min离心10 min,制备血浆,于-20 ℃保存待测。
表1 饲粮组成及营养水平(风干基础)

Table 1 Composition and nutrient levels of diets (air-dry basis) %

项目
Items		 组别Groups
对照Control LCP1 LCP2 LCP3
原料Ingredients
玉米Corn 55.000 59.500 62.500 66.600
豆粕Soybean meal (43% CP) 24.400 20.400 16.500 12.000
石粉Limestone 9.200 9.200 9.200 9.200
大豆油Soybean oil 1.000 0.500 0.500
玉米干酒糟及其可溶物Corn DDGS 8.000 8.000 8.000 9.000
L-赖氨酸硫酸盐L-Lys·H2SO4(70%) 0.100 0.280 0.450 0.630
DL-蛋氨酸DL-Met (99%) 0.170 0.190 0.210 0.230
L-苏氨酸L-Thr (98%) 0.030 0.090 0.150 0.210
氯化钠NaCl 0.300 0.300 0.300 0.300
氯化胆碱Choline chloride (60%) 0.100 0.100 0.100 0.100
植酸酶Phytase 0.015 0.015 0.015 0.015
甜菜碱Betaine 0.020 0.020 0.020 0.020
矿物质预混料Mineral premix1) 0.100 0.100 0.100 0.100
维生素预混料Vitamin premix2) 0.015 0.015 0.015 0.015
磷酸氢钙CaHPO4 0.900 0.960 1.000 1.000
稻壳粉Rice hull powder 0.650 0.330 0.940 0.580
合计Total 100.000 100.000 100.000 100.000
营养水平Nutrient levels3)
代谢能ME/(MJ/kg) 11.05 11.05 11.05 11.05
粗蛋白质CP 17.30 16.40 15.30 13.20
粗脂肪EE 3.85 3.25 3.35 3.05
钙Ca 3.82 4.21 4.29 3.91
总磷TP 0.52 0.54 0.50 0.46
有效磷AP 0.28 0.28 0.28 0.28
蛋氨酸Met 0.43 0.46 0.46 0.43
蛋氨酸+半胱氨酸Met+Cys 0.72 0.75 0.75 0.72
赖氨酸Lys 1.00 1.00 1.03 0.97
苏氨酸Thr 0.70 0.72 0.72 0.68
异亮氨酸Ile 0.75 0.69 0.62 0.51
精氨酸Arg 1.06 0.97 0.87 0.70
缬氨酸Val 0.82 0.75 0.69 0.60

1)矿物质预混料为每千克饲粮提供 The mineral premix provided the following per kg of diets:Cu 10.8 mg,Fe 66 mg,Zn 80 mg,Mn 78 mg,I 1 mg,Se 0.3 mg。

2)维生素预混料为每千克饲粮提供 The vitamin premix provided the following per kg of diets:VA1 1 800 IU,VD3 3 600 IU,VE 21 IU,VK3 4.2 mg,VB1 3 mg,VB2 10.2 mg,叶酸 folic acid 0.9 mg,泛酸钙 calcium pantothenate 15 mg,烟酸 nicotinic acid 45 mg,VB12 0.024 mg,生物素 biotin 0.15 mg。

3)代谢能、有效磷为计算值,其余均为实测值。ME and AP were calculated values, while the others were measured values.

1.2 饲养管理

采用封闭式环控系统,3层H型笼养,每笼4只鸡,环境温度为(28±3) ℃,鸡舍相对湿度为(65±5)%,16 h光照+8 h黑暗。试验鸡每日06:00和14:00各喂料1次,自由采食和饮水,每日清粪1次,常规免疫和管理。正试期第1天和最后1天,固定鸡笼位置,每重复挑选2笼鸡禁食12 h后空腹称重,监测鸡群体重变化。

1.3 测定指标及方法

1.3.1 饲粮营养成分

饲粮各原料代谢能设计值参考《中国饲料成分及营养价值表(2020年第31版)》[11]。饲粮水分含量采用GB/T 6435—2014《饲料中水分的测定》方法测定,CP含量采用GB/T 6432—2018《饲料中粗蛋白的测定 凯氏定氮法》方法测定,粗脂肪含量采用GB/T 6433—2006《饲料中粗脂肪的测定》方法测定,钙含量采用GB/T 6436—2018《饲料中钙的测定》方法测定,总磷含量采用GB/T 6437—2018《饲料中总磷的测定 分光光度法》方法测定,AA含量采用GB/T 15399—2018《饲料中含硫氨基酸的测定 离子交换色谱法》方法测定。

1.3.2 生产性能

试验期间,以重复为单位每日记录死淘数、产蛋数及蛋重,每周结算采食量,计算产蛋率、平均蛋重、日产蛋量、ADFI及料蛋比。

1.3.3 蛋品质

于正试期第4周和第8周进行蛋品质测定,每重复随机选取15枚鸡蛋测定蛋品质指标。其中,蛋白高度、蛋黄颜色和哈氏单位使用多功能蛋品质自动分析仪(EMT-5200,Robotmation公司,日本)进行测定,蛋壳强度使用蛋壳强度分析仪(EFG-0503,Robotmation公司,日本)进行测定,蛋壳厚度使用游标卡尺进行测定。

1.3.4 血浆生化指标

血浆总蛋白(total protein,TP)、白蛋白(albumin,ALB)、球蛋白(globulin,GLB)和尿酸(uric acid,UA)含量均采用南京建成生物工程研究所试剂盒测定。

1.3.5 养分代谢率

代谢试验结束后,将保存于冰箱中的新鲜粪样烘干粉碎后过40目筛,以重复为单位将4 d粪样混匀,用于测定水分、CP和AA含量。CP含量采用南京建成生物工程研究所试剂盒测定,AA含量采用GB/T 18246—2019《饲料中氨基酸的测定》方法测定,水分含量采用GB/T 6435—2014《饲料中水分的测定》方法测定。CP和AA代谢率采用以下公式计算:
代谢率(%)=[饲粮养分含量(%)×采食量(g)-粪便养分含量(%)×排粪量(g)]/[饲粮养分含量(%)×采食量(g)]。

1.3.6 排泄参数

粪便中CP、UA和尿素氮(urea nitrogen,UN)含量均采用南京建成生物工程研究所试剂盒测定。平均日粪氮排泄量采用以下公式计算:
平均日粪氮排泄量[g/(d·只)]=粪便CP含量(%)×排粪量(g)×16%/4(d)/2(只)。

1.4 数据处理

采用SPSS 20.0软件对试验数据进行单因素方差分析(one-way ANOVA),并采用Duncan氏法进行多重比较,P<0.05为差异显著,结果以平均值和均值标准误(SEM)表示。

2 结果

2.1 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期生产性能的影响

由表2可知,各试验阶段(第1~4周、第5~8周和第1~8周),各组间产蛋率和料蛋比均无显著差异(P>0.05)。对照组各试验阶段平均蛋重均显著高于低蛋白质组(P<0.05),LCP1组和LCP2组同时期平均蛋重无显著差异(P>0.05),但均显著高于LCP3组(P<0.05)。日产蛋量和ADFI数据结果与平均蛋重相类似,LCP1组和LCP2组同时期日产蛋量和ADFI与对照组相比均无显著差异(P>0.05),但均显著高于LCP3组(P<0.05)。
表2 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期生产性能的影响

Table 2 Effects of low protein diet on performance of Lohmann Pink laying hens during late laying period

项目
Items		 时间
Time		 组别Groups 均值
标准误
SEM		 P值
P-value
对照Control LCP1 LCP2 LCP3
预试期Adaptation period 83.73 83.97 83.92 83.82 0.48 0.524
产蛋率 第1~4周Weeks 1 to 4 83.11 82.75 83.59 81.64 0.49 0.559
Laying rate/% 第5~8周Weeks 5 to 8 81.20 81.66 82.47 80.32 0.48 0.480
第1~8周Weeks 1 to 8 82.16 82.20 83.03 80.98 0.47 0.524
预试期Adaptation period 64.43 64.03 64.38 64.10 0.87 0.279
平均蛋重 第1~4周Weeks 1 to 4 64.72a 64.05b 63.77b 62.33c 0.19 <0.001
Average egg weight/g 第5~8周Weeks 5 to 8 65.25a 64.45b 64.13b 62.40c 0.23 <0.001
第1~8周Weeks 1 to 8 64.95a 64.27b 63.93b 62.37c 0.21 <0.001
预试期Adaptation period 53.94 53.77 54.01 53.74 0.31 0.989
日产蛋量 第1~4周Weeks 1 to 4 53.77a 53.00a 53.31a 50.87b 0.38 0.022
Daily egg mass/g 第5~8周Weeks 5 to 8 52.97a 52.65a 52.87a 50.12b 0.39 0.017
第1~8周Weeks 1 to 8 53.38a 52.82a 53.09a 50.50b 0.38 0.017
预试期Adaptation period 118.1 116.7 116.4 115.8 0.4 0.249
平均日采食量 第1~4周Weeks 1 to 4 120.9a 119.8a 119.9a 115.6b 0.5 <0.001
ADFI/g 第5~8周Weeks 5 to 8 119.8a 118.2a 117.5a 112.5b 0.8 0.003
第1~8周Weeks 1 to 8 120.3a 119.0a 118.5a 114.1b 0.6 <0.001
预试期Adaptation period 2.19 2.17 2.16 2.16 0.01 0.743
料蛋比 第1~4周Weeks 1 to 4 2.25 2.26 2.25 2.27 0.13 0.908
Feed/egg 第5~8周Weeks 5 to 8 2.26 2.25 2.22 2.25 0.14 0.830
第1~8周Weeks 1 to 8 2.26 2.26 2.24 2.26 0.12 0.930

同行数据肩标无字母或相同字母表示差异不显著(P>0.05),不同字母表示差异显著(P<0.05)。下表同。

In the same row, values with no letter or the same letter superscripts mean no significant difference (P>0.05), while with different letter superscripts mean significant difference (P<0.05). The same as below.

2.2 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期蛋品质的影响

由表3可知,试验第4周和第8周的蛋品质指标数据显示,各组间蛋白高度、哈氏单位和蛋壳强度均无显著差异(P>0.05),而蛋黄颜色随饲粮CP水平的提升而不断降低,且低蛋白质组与对照组之间存在显著差异(P<0.05)。第4周蛋壳厚度数据显示,LCP1组和LCP2组蛋壳厚度与对照组相比无显著差异(P>0.05),而LCP3组蛋壳厚度显著高于对照组(P<0.05),但该差异未能持续至第8周,即第8周各组间蛋壳厚度无显著差异(P>0.05)。
表3 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期蛋品质的影响

Table 3 Effects of low protein diet on egg quality of Lohmann Pink laying hens during late laying period

项目
Items		 时间
Time		 组别Groups 均值
标准误
SEM		 P值
P-value
对照Control LCP1 LCP2 LCP3
蛋白高度 第4周Week 4 8.12 8.08 8.41 8.29 0.27 0.592
Albumen height/mm 第8周Week 8 8.33 8.25 8.34 8.19 0.20 0.850
蛋黄颜色 第4周Week 4 7.82c 8.16b 8.21b 8.54a 0.10 <0.001
Yolk color 第8周Week 8 8.29c 8.62b 8.81ab 9.03a 0.14 <0.001
哈氏单位 第4周Week 4 88.5 88.7 89.9 89.9 1.3 0.552
Haugh unit 第8周Week 8 90.0 89.4 89.8 88.8 1.1 0.741
蛋壳厚度 第4周Week 4 0.347b 0.355ab 0.356ab 0.365a 0.005 0.012
Eggshell thickness/mm 第8周Week 8 0.347 0.349 0.347 0.347 0.010 0.997
蛋壳强度 第4周Week 4 43.0 43.0 43.9 45.2 1.3 0.336
Eggshell strength/(N/cm2) 第8周Week 8 41.9 42.9 41.9 41.3 0.8 0.246

2.3 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期血浆生化指标的影响

由表4可知,LCP1组和LCP2组血浆TP含量与对照组相比无显著差异(P>0.05),而LCP3组血浆TP含量显著高于其他3组(P<0.05)。各组间血浆ALB与GLB含量均无显著差异(P>0.05)。血浆UA含量随饲粮CP水平的提升而不断升高,低蛋白质组血浆UA含量均显著低于对照组(P<0.05),且LCP3组血浆UA含量显著低于LCP1组(P<0.05)。
表4 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期血浆生化指标的影响

Table 4 Effects of low protein diet on plasma biochemical indices of Lohmann Pink laying hens during late laying period

项目
Items		 组别Groups 均值标准误
SEM		 P值
P-value
对照Control LCP1 LCP2 LCP3
总蛋白TP/(g/L) 46.6b 46.1b 44.1b 52.6a 2.5 0.029
白蛋白ALB/(g/L) 13.0 13.8 12.2 15.3 1.1 0.057
球蛋白GLB/(g/L) 33.6 32.3 31.9 37.3 2.5 0.140
尿酸UA/(μmol/L) 293.9a 234.3b 205.1bc 166.7c 24.2 <0.001

2.4 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期CP和AA代谢率的影响

由表5可知,与对照组相比,LCP1组和LCP2组CP代谢率无显著差异(P>0.05),但均显著高于LCP3组(P<0.05)。与对照组相比,LCP1组和LCP2组Lys、Met和Thr代谢率显著提高(P<0.05),而LCP3组Lys、Met和Thr代谢率无显著差异(P>0.05)。此外,与对照组相比,LCP3组精氨酸(Arg)、缬氨酸(Val)和异亮氨酸(Ile)代谢率显著降低(P<0.05),而LCP1组和LCP2组Arg、Val和Ile代谢率无显著差异(P>0.05)。
表5 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期CP和AA代谢率的影响

Table 5 Effects of low protein diet on metabolic rates of CP and AA of Lohmann Pink laying hens during late laying period %

项目
Items		 组别Groups 均值标准误
SEM		 P值
P-value
对照Control LCP1 LCP2 LCP3
粗蛋白质CP 39.2ab 45.3a 46.1a 35.2b 3.2 0.018
赖氨酸Lys 85.1b 87.0a 88.1a 84.7b 0.8 0.005
蛋氨酸Met 90.0b 92.3a 91.6a 90.4b 0.5 0.004
苏氨酸Thr 80.8b 84.1a 83.2a 80.8b 1.0 0.020
精氨酸Arg 91.0a 91.4a 91.3a 86.5b 0.9 0.001
缬氨酸Val 84.7a 85.1a 83.8a 79.2b 1.2 0.002
异亮氨酸Ile 87.7a 87.7a 86.5a 81.5b 1.0 <0.001

2.5 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期排泄参数的影响

由表6可知,粪便CP、UA和UN含量及平均日氮排泄量数据结果相类似,即随着饲粮CP水平的降低,各排泄参数均不断下降。其中,LCP1组和LCP2组粪便CP和UA含量与对照组相比无显著差异(P>0.05),而LCP3组粪便CP和UA含量显著低于对照组(P<0.05)。LCP1组粪便UN含量与对照组相比无显著差异(P>0.05),但二者均显著高于LCP2组和LCP3组(P<0.05)。低蛋白质饲粮组平均每日氮排泄量均显著低于对照组(P<0.05),且3个低蛋白质饲粮组间差异不显著(P>0.05)。
表6 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期排泄参数的影响

Table 6 Effects of low protein diet on excretion parameters of Lohmann Pink laying hens during late laying period

项目
Items		 组别Groups 均值标准误
SEM		 P值
P-value
对照Control LCP1 LCP2 LCP3
粗蛋白质含量CP content/% 23.00a 24.73a 20.44ab 16.54b 2.44 0.011
尿酸含量UA content/(μmol/g) 12.26a 12.71a 11.51a 9.24b 0.96 0.002
尿素氮含量UN content/(mmol/g) 0.051a 0.046a 0.037b 0.030b 0.004 <0.001
平均日粪氮排泄量
Average daily N excretion/
[g/(d·只)]		 1.870a 1.421b 1.236b 1.291b 0.110 0.001

3 讨论

3.1 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期生产性能的影响

本研究发现,罗曼粉蛋鸡产蛋后期饲粮补充Lys、TSAA和Thr水平分别至1.03%、0.75%和0.72%,饲粮CP水平降低至15.3%,对其产蛋率、ADFI、日产蛋量和料蛋比均无显著影响,但平均蛋重较对照组(CP水平为17.3%)显著降低,这与前人研究结果相类似。付胜勇[12]研究报道,21~34周龄海兰灰蛋鸡在标准回肠可消化氨基酸模式下降低饲粮CP水平至16%,其平均蛋重显著降低,但产蛋率和日产蛋量显著提高。任冰[13]按照理想氨基酸模式,降低饲粮CP水平至15%,可提高21~32周龄海兰灰蛋鸡产蛋率,对ADFI、日产蛋量和料蛋比无显著影响,有降低平均蛋重的趋势。Zhou等[5]报道,24~34周龄海兰褐蛋鸡饲粮CP水平由16.5%降低至14%,补充丝氨酸后其生产性能可保持稳定,甚至优于对照组(CP水平为16.5%)。然而,也有研究得出相反的结论,Meluzzi等[14]发现,相比对照组饲粮(CP水平为17%),低蛋白质饲粮(CP水平为15%)会导致24~40周龄海兰灰蛋鸡产蛋率和日产蛋量显著下降,料蛋比显著上升;Azzam等[15]报道,28~40周龄罗曼褐蛋鸡饲粮CP水平由16.18%降低至14.16%会对其产蛋率和日产蛋量造成负面影响。值得注意的是,本研究在平衡饲粮Lys、TSAA和Thr水平的条件下,饲粮CP水平降低至13.2%,其产蛋率虽与对照组差异不显著,但相比LCP1组(CP水平为16.4%)和LCP2组(CP水平为15.3%)降幅较大。

3.2 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期蛋品质的影响

本试验结果表明,与对照组相比,罗曼粉蛋鸡产蛋后期饲粮CP水平降低至15.3%显著降低了平均蛋重,显著提高了蛋黄颜色,但对蛋白高度、哈氏单位、蛋壳强度和蛋壳厚度均无显著影响,这与前人研究结果相类似。Ji等[7]研究发现,低蛋白质饲粮降低了海兰W36蛋鸡21~34周龄平均蛋重。低蛋白质饲粮对蛋黄颜色的提升作用,主要是由于饲粮中玉米添加量较高,进而导致饲粮中叶黄素水平升高[16]。Leeson等[17]研究发现,52~60周龄蛋鸡饲粮CP水平降低至14.4%,平均蛋重较对照组(CP水平为16.8%)显著降低,并推测蛋重降低是由于总氮摄入不足导致的。

3.3 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期血浆生化指标的影响

血浆TP、ALB和UA含量能反映机体蛋白质的代谢情况,血浆GLB含量则反映机体免疫水平[18]。本研究发现,随着饲粮CP水平的下降,蛋鸡血浆UA含量不断下降。Namroud等[19]使用CP水平为17%~23%的饲粮饲喂罗斯(Ross)308肉鸡,发现低蛋白质饲粮显著降低了28日龄Ross 308肉鸡血浆UA含量。Kriseldi等[20]通过肉鸡低蛋白质饲粮研究发现,饲粮CP水平的降低同样伴随着血浆UA含量的降低,并推测高蛋白质饲粮提高血浆UA含量的原因可能是由于过量氮的摄入导致。当饲粮CP水平降低时,机体摄入AA总量也一并减少,作为家禽AA代谢的最终产物,UA的合成也必然降低[21]。血浆ALB具有作为养分运输的载体、抑制自由基的产生以及维持渗透压平衡和酸碱平衡等功能[22]。本试验中,饲粮CP水平由17.3%降低至15.3%,对血浆TP、ALB和GLB含量均无显著影响。齐明星等[23]研究发现,高能低蛋白质饲粮(代谢能为11.08 MJ/kg,CP水平为15%)显著提高了蛋鸡血清ALB含量,推测该现象与蛋白质的合成代谢有关,其机理还需进一步研究。然而,本试验中,饲粮CP水平降低至13.2%时,血浆TP、ALB和GLB含量均有提升,其中血浆TP含量的提升达到显著水平,这与Kriseldi等[20]的研究结果相反,其原因有待进一步探究。

3.4 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期CP和AA代谢率的影响

本试验结果显示,饲粮CP水平降低至15.3%时,可显著提高蛋鸡产蛋后期对Lys、Met和Thr代谢率,对CP代谢率也有一定提升,但未达到显著水平。关于低蛋白质饲粮对蛋鸡养分代谢率的研究报道较少。孟艳莉等[10]报道,蛋鸡饲粮CP水平降低1个百分点且添加蛋白酶时,CP消化率提高了44.39%。Dao等[24]同样发现,低蛋白质饲粮能够提高蛋鸡CP消化率。Teng等[25]对14日龄科宝(Cobb)500肉鸡进行艾美球虫攻毒后,进一步开展低蛋白质饲粮试验并发现,与对照组(未进行球虫攻毒,CP水平为19%)相比,降低饲粮CP水平至16%并添加Arg、Met、Thr和谷氨酸(Glu)显著提高了23日龄肉鸡对Arg、Met、Thr和Glu的表观代谢率,但对其他AA代谢率无显著影响,这与本试验的相似之处在于二者只提升了饲粮中已平衡的AA代谢率,而对未平衡的AA代谢率均无提升作用。然而,Ploudel等[26]研究发现,与对照组(CP水平为16.9%~17.5%)相比,30~50周龄海兰W36蛋鸡降低饲粮CP水平3个百分点(平衡Lys、Met、Thr、Trp、Ile和Val)对50周龄上述AA代谢率均无显著影响。值得注意的是,本试验中饲粮CP水平降低至13.2%时,与对照组相比,未对CP、Lys、Met和Thr的代谢率产生负面影响,但Arg、Val和Ile代谢率显著降低,这可能与本试验中只平衡了Lys、TSAA和Thr有关。

3.5 低蛋白质饲粮对罗曼粉蛋鸡产蛋后期排泄参数的影响

本试验发现,饲粮CP水平降低至16.4%及以下时,可显著降低平均日粪氮排泄量;饲粮CP水平降低至15.3%及以下时,可显著降低粪便UN含量;饲粮CP水平降低至13.2%时,可显著降低粪便CP和UA含量。前人研究已多次论证,低蛋白质饲粮可显著降低蛋鸡粪氮排泄量[3,9,24],其原因可能是低蛋白质饲粮对蛋鸡采食量无显著影响,即直接降低了蛋鸡CP日摄入量,同时提高了AA利用率,从而降低了UA合成,最终减少了粪氮排泄[21]。
不过,值得注意的是,本试验中饲粮CP水平由15.3%降低至13.2%,跨度较大,仍需通过更小的梯度设计来探究维持罗曼粉产蛋后期生产性能、蛋品质保持稳定的最低CP需要量。

4 结论

综上所述,在平衡饲粮Lys、TSAA和Thr水平的前提下,饲粮CP水平降低至15.3%时,对罗曼粉蛋鸡产蛋后期(62~70周龄)生产性能和蛋品质无负面影响,且提高了CP和AA代谢率,降低了粪氮排泄量。然而,当饲粮CP水平降低至13.2%时,对产蛋后期平均蛋重和AA代谢率有一定负面作用。

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