畜牧兽医学报  2019, Vol. 50 Issue (8): 1614-1624. DOI: 10.11843/j.issn.0366-6964.2019.08.010    PDF    
用湿筛分测定猪颗粒饲料、肠道食糜及粪便粒径的研究
高庆涛, 赵峰, 张虎, 王亚     
中国农业科学院北京畜牧兽医研究所 动物营养学国家重点实验室, 北京 100193
摘要:旨在探讨湿筛分过程中用水量、上样量及筛分时间对猪颗粒饲料、肠道食糜及粪便平均粒径测定的影响,为猪颗粒饲料、肠道食糜及粪便粒径的测定提供参考。本研究选用标准筛孔径分别为2.0、1.0、0.5、0.25、0.106和0.072 mm套筛进行湿筛分测定平均粒径。采用3×2×2三因素完全随机设计,筛分过程中用水量设1、1.25或1.5 L;上样量分别为颗粒料7.5或10 g,回肠食糜15或30 g,粪便10或20 g;筛分时间分别为4或5 min。每种类型样品共12个处理。结果表明:1)在各层筛上物质量占比中,随用水量的增加,颗粒料、回肠食糜及粪便中1 mm以上颗粒质量占比显著下降(P < 0.05),可溶物质量占比显著上升(P < 0.05);随上样量的增加,1 mm以上颗粒质量占比显著上升(P < 0.05),可溶物或0.072 mm以下颗粒质量占比显著下降(P < 0.05);而筛分时间对各层筛筛上物质量的占比均没有显著影响。2)用水量、上样量对颗粒料、回肠食糜及粪便平均粒径的测定均有极显著影响(P < 0.01),筛分时间仅对食糜测定结果有显著影响(P < 0.05),但仅相差4 μm。用水量为1 L时测定的平均粒径均显著高于1.25和1.5 L(P < 0.05),而1.25和1.5 L仅在粪便的测定结果有显著差异(P < 0.05),在颗粒料和回肠食糜的测定结果无显著差异。颗粒饲料上样量7.5~10 g,食糜上样量15~30 g,粪便上样量10~20 g时,粒径测定结果的差异均在12 μm以内。综上,在测定猪颗粒饲料、食糜及粪便的粒径时,颗粒饲料上样量7.5~10 g,食糜上样量15~30 g,粪便上样量10~20 g,用水量1.25 L,筛分时间4 min获得的测定结果相对稳定。
关键词湿筛分    颗粒料    食糜    粪便    粒径    筛分条件    
Determination of the Particle Size for Pelleted Diet, Digesta and Feces of Pig Using Wet-sieving Method
GAO Qingtao, ZHAO Feng, ZHANG Hu, WANG Ya     
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
Abstract: This study was conducted to investigate the effects of water volume, sample weight and sieving time on the mean particle size of pelleted diet, digesta and feces during wet-sieving, and to provide a reference for the determination of particle size for pelleted diet, digesta and feces of pig. The mean particle size was assayed with wet-sieving using a set of 6 sieves sized 2.0, 1.0, 0.5, 0.25, 0.106 and 0.072 mm. The water volume of 1, 1.25 or 1.5 L, sample weight of 7.5 or 10 g for pelleted diet, 15 or 30 g for ileal digesta, 10 or 20 g for feces and sieving time of 4 or 5 min were used in a 3×2×2 factorial completely randomized arrangement. There were 12 treatments for each type of sample. The effect of wet-sieving conditions on the measurement of geometric mean particle size of samples was investigated. The results showed that:1) Increment of water volume significantly decreased the proportion of the mass content of the particles more than 1 mm in size(P < 0.05), but significantly increased the proportion of the mass content of soluble matter in pelleted diet, ileal digesta and feces (P < 0.05); Increment of the sample weight significantly increased the proportion of the mass content of the particles more than 1 mm in size(P < 0.05), but significantly decreased the proportion of the mass content of soluble matter or particles less than 0.072 mm (P < 0.05). However, there was no significant effect of sieving time on the proportion of the mass content on each sieves. 2) Water volume and sample weight extremely significantly affected the determination of mean particle size for pelleted diet, ileal digesta and feces (P < 0.01), but significant effect of the sieving time was only observed on the determination of ileal digesta(P < 0.05). The determined value of mean particle size was significantly higher in 1 L of water volume than 1.25 or 1.5 L (P < 0.05). Moreover, particle size was significantly different between 1.25 and 1.5 L of water volume for feces (P < 0.05), but there was no significant differences between 1.25 and 1.5 L of water volume for ileal digesta and pelleted diet. The sample weight of pelleted diet ranged from 7.5 to 10 g, ileal digesta from 15 to 30 g, and feces from 10 to 20 g led to the difference of less than 12 μm in determined particle size. In summary, in the determination of particle size for pelleted diet, digesta and feces of pig using wet-sieving method, the sample weight of pelleted diet ranged from 7.5 to 10 g, ileal digesta from 15 to 30 g, feces from 10 to 20 g, 1.25 L of water volume and 4 min of sieving time are the optimized condition to obtain a relatively stable result.
Key words: wet-sieving     pelleted diet     digesta     feces     particle size     sieving conditions    

饲料的粉碎粒径、肠道食糜乃至粪便的粒径均在一定程度上与养分的消化率有关。因此,测定饲粮或食糜的粒径对探讨动物体内的消化过程有重要意义[1-3]。目前,对单一饲料原料或配合饲料的粉料可通过GB/T5917-2008、ANSI/ASAES 319.4[4]以及Kalivoda等[5]方法测定。而对于食糜或粪便粒径的测定主要采用湿筛分法,选用6或9层套筛,用1.3~2 L去离子水对7.5~30 g样品进行循环冲洗,筛分5~10 min,然后计算平均粒径。如Maulfair等[6]在评估奶牛瘤胃食糜的粒径,Uden和Van Soest[7]在测定反刍动物肠道食糜或粪便的粒径,Jankowski等[8]、Lentle等[9]和Fritz等[10]在测定家禽肠道食糜或粪便的粒径时均采用了此法。然而,不同的研究者在测定动物肠道食糜及粪便的粒径时,在上样量、用水量以及筛分时间的参数上有较大的变化,同时,饲粮制粒后如何测定其粉碎粒径也鲜见相关文献报道。

为此,本试验以6层套筛为基础,研究湿筛分法测定不同类型样品(颗粒饲料、食糜和粪便)粒径时适宜的用水量、上样量及筛分时间。建立湿筛分测定猪颗粒饲料、食糜及粪便粒径的方法,为饲粮经过猪体内消化到粪便的形成过程中粒径变化规律的研究提供参考。

1 材料与方法 1.1 饲粮、食糜及粪便的采集

以玉米经过2 mm孔径筛片、豆粕经过1.5 mm孔径筛片粉碎后配制的全价配合饲粮(组成:玉米66.69%,豆粕22.2%,标粉5%,豆油1.18%,矿物质、维生素、氨基酸及其他共4.93%)经蒸汽调制制成颗粒试验饲粮。颗粒料、回肠食糜及粪便养分含量见表 1。选用6头回肠瘘管猪(试验期初始体重(29.1±1.58) kg),饲喂试验饲粮, 在5 d收集期的第1、3、5天收集食糜样品,第2、4天收集粪便样品。将每次收集的样品混合,并倒入总收集瓶中,最后将所有的回肠食糜、粪便分别混合均匀制备成相应的样品,-20 ℃冷冻保存。其中,回肠食糜在4 ℃、1 250 g条件下离心10 min,收取残渣。

表 1 颗粒料、回肠食糜及粪便养分含量 Table 1 Composition of pelleted diet, ileal digesta and feces
1.2 试验设计

本研究采用3×2×2三因素完全随机设计研究样品在湿筛分过程中用水量、上样量以及筛分时间对几何平均粒径测值的影响。其中用水量分别为1、1.25或1.5 L;上样量分别为颗粒料7.5或10 g,回肠食糜15或30 g,粪便10或20 g;筛分时间分别为4或5 min,每种类型样品共12个处理。

1.3 湿筛分的测定过程

准确称取一定量样品,按GB/T 6435-2014同步测定样品干物质含量。样品前处理和标准筛孔径的选择参考Lentle等[9]的方法。用100 mL去离子水浸泡15或30 min,使样品充分分散,选择的标准筛孔径分别为2.0、1.0、0.5、0.25、0.106和0.072 mm。将样品转移至2 mm孔径的标准筛中加去离子水进行冲洗筛分,冲洗液用烧杯接收,使冲洗液液面没过筛底,摇动标准筛进行筛分(90~100次·min-1)。然后,将全部冲洗液倒入1 mm孔径的标准筛,用去离子水冲洗残留在烧杯上的样品,以另一烧杯接收过筛冲洗液,同样使冲洗液液面没过筛底,摇动标准筛进行筛分(90~100次·min-1)。重复上述步骤,依次经过0.5、0.25、0.106和0.072 mm孔径的标准筛。筛分后各层筛上物转移到已烘干称重的锡箔盒中,105 ℃烘干、称重,参照Clauss等[11]的方法计算平均粒径。

1.4 数据处理与统计分析

平均粒径计算公式:${d_{MEAN}} = \sum\limits_{i = 1}^n {{p_i} \times \frac{{{S_i} + {S_{i + 1}}}}{2}} $

其中,pi为第i层筛上物占总样重的百分比;Si为第i层筛的孔径。

采用SAS 9.0的MEANS模块计算基本统计量。采用GLM模块对不同处理下的筛上物比例、平均粒径进行方差分析,平均值以Duncan氏法进行多重比较。

2 结果 2.1 用水量、上样量及筛分时间对颗粒饲料粉碎粒径测定的影响

用水量、上样量对颗粒饲料粒径的测定均有极显著影响(P < 0.01,表 2)。当用水量为1.5 L时,平均粒径为512 μm,比用水量为1 L时降低28 μm(P < 0.05),与用水量为1.25 L时无显著差异。在粒径分级中,与用水量1 L相比,用水量增至1.25和1.5 L,1 mm以上颗粒质量占比显著降低(P < 0.01),0.25~0.5 mm之间颗粒及可溶物质量占比显著升高(P < 0.01)。用水量1.25和1.5 L之间各层筛上物质量占比均无显著差异。上样量为7.5 g时,平均粒径为514 μm,比上样量为10 g时平均粒径降低10 μm(P < 0.05)。在粒径分级中,与上样量7.5 g相比,上样量增至10 g,1 mm以上颗粒质量占比显著升高,可溶物质量占比显著降低(P < 0.05),0.072~1 mm之间颗粒质量占比无显著差异。用水量和上样量存在显著的交互作用(P < 0.05)。当用水量为1 L时,7.5和10 g上样量间平均粒径相差较大(19 μm),而用水量为1.25~1.5 L时,7.5和10 g上样量间平均粒径相差较小(6 μm)。筛分时间对各层筛上物占比均无显著影响。筛分时间从4 min增加到5 min后,虽然平均粒径的测定结果有降低的趋势,但相差较小(4 μm)。

表 2 不同处理对颗粒料各层筛上物占比和平均粒径的影响 Table 2 Effects of different treatments on the proportion of particles retained on each sieve and mean particle size of pelleted diet
2.2 用水量、上样量及筛分时间对回肠食糜粒径测定的影响

用水量、上样量对回肠食糜粒径的测定均有极显著影响(P < 0.01,表 3)。当用水量为1.5 L时,平均粒径为333 μm,比用水量为1 L时降低16 μm(P < 0.05),与用水量为1.25 L时无显著差异。在粒径分级中,与用水量1 L相比,用水量增至1.25和1.5 L,1.0 mm以上颗粒和0.072~0.106 mm之间颗粒质量占比显著降低(P < 0.01),可溶物质量占比显著升高(P < 0.01)。用水量1.25和1.5 L之间各层筛上物质量占比均无显著差异。上样量为15 g时,平均粒径为333 μm,比上样量为30 g时平均粒径降低12 μm(P < 0.05)。在粒径分级中,与上样量15 g相比,上样量增至30 g,0.5 mm以上颗粒质量占比显著升高(P < 0.05),可溶物质量占比显著降低(P < 0.05),0.072~0.5 mm之间颗粒质量占比无显著差异。用水量和上样量无显著的交互作用。筛分时间对各层筛上物占比均无显著影响。筛分时间从4 min增加到5 min后,虽然平均粒径的测定结果显著降低(P < 0.05),但仅相差4 μm。

表 3 不同处理对回肠食糜各层筛上物占比和平均粒径的影响 Table 3 Effects of different treatments on the proportion of particles retained on each sieve and mean particle size of ileal digesta
2.3 用水量、上样量及筛分时间对粪便粒径测定的影响

用水量、上样量对粪便粒径的测定均有极显著影响(P < 0.01,表 4)。当用水量为1.5 L时,平均粒径为256 μm,比用水量为1 L时降低37 μm(P < 0.05),与用水量为1.25 L时有显著差异(P < 0.05),仅相差6 μm。在粒径分级中,与用水量1 L相比,用水量增至1.25和1.5 L,0.5 mm以上颗粒和0.072~0.25 mm之间颗粒质量占比显著降低(P < 0.05),0.25~0.5 mm之间颗粒质量和可溶物质量占比显著升高(P < 0.05)。用水量1.25和1.5 L间,仅1 mm以上颗粒和可溶物质量占比存在显著差异(P < 0.05),0.072~1 mm之间颗粒质量占比无显著差异。上样量为10 g时,平均粒径为268 μm,比上样量为20 g时平均粒径降低4 μm(P < 0.05)。在粒径分级中,与上样量10 g相比,上样量增至20 g,1 mm以上颗粒质量占比显著升高(P < 0.05),0.25~0.5 mm和0.072~0. 106 mm之间颗粒质量占比显著降低(P < 0.05)。用水量和上样量无显著的交互作用。筛分时间对各层筛上物占比均无显著影响。筛分时间从4 min增加到5 min后,平均粒径的测定结果有降低的趋势,但相差较小(2 μm)。

表 4 不同处理对粪便各层筛上物占比和平均粒径的影响 Table 4 Effects of different treatments on the proportion of particles retained on each sieve and mean particle size of feces
3 讨论

饲料经过动物消化形成粪便的过程中,总体上呈现水溶性成分占比逐渐增加,几何平均粒径逐渐减少的变化规律[9, 12]。本试验中,猪颗粒饲料、回肠食糜、粪便的可溶物比例分别约为28%、45%和56%,相应的几何平均粒径约为520、340和270 μm。这与饲料在沿着猪消化道被消化吸收的过程中受物理、化学及微生物消化后,单位重量的底物表面积逐步增大的规律相一致[13]。由于饲料、食糜、粪便的水分含量分别约为14%、90%和70%[14-16],粒径的分布比例也相差较大,因此,在湿筛分法测定中套筛的选择、上样量、用水量、筛分时间均应有所不同。套筛的选择原则一般是让绝大部分的物质能通过最大孔径的分筛。如在奶牛食糜与粪便粒径的测定中,由于粗饲料的直径较长,因此选择的套筛孔径为0.15~9.5 mm[6, 17]。鸡饲料通常采用3 mm以上筛孔的粉碎机粉碎[18-19],因此,在测定食糜或粪便粒径时套筛的孔径为0.072~2 mm[8-9];而猪饲料原料在锤片式粉碎机一般经过1.5~3.2 mm筛孔粉碎,其几何平均粒径可以达到400~600 μm[20-22]。因此,本试验选择0.072~2 mm的套筛,2 mm孔径的分筛基本能让所有的物质通过,而1 mm孔径分筛的筛上物占比在3%~15%之间,这表明套筛的选择合适。

在颗粒饲料粒径的测定上,目前GB/T5917-2008[23]、ANSI/ASAES 319.4[4]等常规方法仅适用于对固态的粉料进行测定,而当粉料经制粒形成颗粒饲料的过程中粒径会减小[1, 24-26]。Lentle等[9]报道了采用湿筛分的方法测定冷制粒肉鸡颗粒饲料的粒径,其在Waghorn[12]提出湿筛分测定奶牛食糜和粪便粒径方法的基础上,提出了对颗粒饲料充分浸泡(水泡10 min)的预处理,采用0.072~2 mm孔径的套筛。然而,在饲料的上样量、冲洗用水量、筛分时间方面并未提供详细参数。在本试验中,借鉴了Lentle等[9]湿筛分法的浸泡预处理,当颗粒饲料上样量7.5~10 g,冲洗用水量1.25 L,筛分4 min时测定的几何平均粒径相对稳定(与相邻条件最小相差约11 μm),且该测定的变异度远低于生产中以饲料粉碎粒径每减少100 μm(1 000~400 μm变化)对应饲料转化率约提高1.3%的试验精度[2, 27-29]。综上,颗粒饲料粒径的湿筛分测定中上述条件较为适宜。

在食糜及粪便粒径的测定中,套筛的孔径不同其上样量、用水量及筛分时间会有所差异。然而在这些参数的确定上都是如何使样品能通过套筛后筛上物的比例达到稳定。Maulfair等[6]在测定奶牛瘤胃食糜的粒径时采用Beauchemin等[30]的方法,选用0.15~9.5 mm共计6层套筛,湿样的上样量为30 g,用去离子水以1.5~2 L·min-1的流速循环冲洗,筛分10 min。Uden和Van Soest[7]在测定犊牛食糜或粪便粒径时,上样量为7.5 g干物质,筛分5 min。Jankowski等[8]以及Lentle等[9]测定肉鸡食糜或粪便的粒径中,先将样品在去离子水中浸泡15或30 min,然后倒入0.072~2 mm共计6层套筛中筛分。其中食糜的上样量为30~50 g,粪便上样量20~30 g,用水1.3 L循环冲洗,筛分5 min。而Fritz等[10]在测定猪、鸡等动物食糜或粪便粒径时,选用0.063~16 mm共计9层套筛,用2 L去离子水循环冲洗,筛分10 min。由此可见,在食糜或粪便粒径的测定中上样量多为3~10 g(以干物质计),冲洗用水量多为1~2 L,筛分时间为5~10 min。本试验中,食糜上样量15~30 g,粪便上样量10~20 g,用水量1.25 L,筛分4 min,几何平均粒径测定结果的变化范围在12 μm之内。因此,上述筛分条件可以作为猪食糜及粪便粒径测定方法的基本参数。

4 结论

在测定猪颗粒饲料、食糜及粪便的粒径时,颗粒饲料上样量7.5~10 g,食糜上样量15~30 g,粪便上样量10~20 g,用水量1.25 L,筛分时间4 min可获得相对稳定的测定结果。

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