动物营养学报    2019, Vol. 31 Issue (12): 5446-5453    PDF    
运动马能量供给优化策略初探
任万路 , 孟军 , 王川坤 , 姚新奎     
新疆农业大学动物科学学院, 乌鲁木齐 830052
摘要: 合理调制运动马饲粮,保证运动马能量充足是充分发挥运动马竞技性能的保障,运动马的能量主要源自饲草中纤维素等结构性多糖的微生物发酵和谷物类饲料中淀粉的消化吸收。粗饲料的营养密度低且消化利用率低,不能满足运动马的能量需求,但粗饲料可有效改善运动马的胃肠和代谢健康;而谷物类饲料的营养密度高,且易于消化吸收,但高谷物饲粮可引致胃肠和代谢性问题。运动马能量供给和代谢健康间存在一定矛盾,需采用适宜的饲料加工工艺、谷物类饲料替代、添加非营养性添加剂及优化饲草给料方式等措施改善运动马高谷物饲粮引致的代谢失衡。本文总结了运动马粗饲料和谷物类饲料的优缺点,并针对性提出了改善运动马能量供给的优化策略。
关键词:     能量供给    纤维素    淀粉    
Improvement Strategies for Dietary Energy Supply of Racehorses
REN Wanlu , MENG Jun , WANG Chuankun , YAO Xinkui     
College of Animal Science, Xinjiang Agriculture University, Urumqi 830052, China
Abstract: The proper adjustment of feed formula, and supply of adequate energy is the guarantee of high performance of racehorses. The two principal energy sources of racehorses are starch of grain feed and structural polysaccharides (such as cellulose) of roughage. The nutrient density, as well as the efficiency of digestion and utilization of roughage are not high enough to meet the energy requirement of racehorse. Whereas, high-fiber feedstuffs, such as hay and straw, could effectively relieve the grain feed induced metabolic disorder. As to grain feed, it contents high concentrations of nutrients, however, high grain diet could cause health problems of the gastrointestinal tract and metabolism. And so, there is a big conflict between energy supply and metabolic health in the process of racehorses breeding. Some effective measures, such as proper processing technology of roughage, the application of alternatives of grain, non-nutritive feed additive, and the feeding methods of roughage, could highly improve metabolic imbalance induced by high grain feed. In this review, we summarized the advantages and shortages of high-fiber and high grain feed of racehorses, and put forward some targeted improve measures.
Key words: racehorse    energy supply    cellulose    starch    

运动马在竞技和训练中以及运动后的身体恢复均需消耗很多能量,Pratt-Phillips等[1]的研究发现运动马的营养需求在NCR(2007)标准的重体力和非常重体力之间。运动马饲粮中的能量因子主要有2类:粗饲料中的纤维素和谷物类饲料中的淀粉,单靠粗饲料并不能满足运动马的能量需求,这就要求在运动马饲粮中补充足够的谷物类饲料。但马是一种后肠发酵动物,其肠道微生物活动主要发生于后肠道,饲粮组成变化会影响肠道菌群结构和后肠道多糖发酵模式,进而引致马消化系统发生功能紊乱,尤其对于运动马,饲粮从高纤维饲粮到高谷物饲粮的转变会导致马胃肠菌群失衡,从而导致其肠道代谢和免疫功能异常,可引致胃肠绞痛甚至死亡[2]。有研究指出,马匹每日淀粉摄入量超过2.0 g/kg BW时就极易导致胃部溃疡[3],而且高谷物饲粮会引致马匹高血糖、胰岛素抵抗等一系列代谢问题,高纤维饲粮(羊茅、苜蓿干草等)可改善断奶马的代谢及胃肠健康状况[4]。高能量的纤维性饲料如窖藏半干草、甜菜浆和大豆皮等,这类饲料易被消化利用,且营养浓度高,可在一定程度上改善马的代谢状况,在运动马饲喂过程中可用高能量的纤维性饲料替代部分谷物[5]。运动马营养和管理统计结果显示在运动马饲喂过程中均存在一些营养不足或代谢异常问题,例如土耳其运动马存在消化能偏低和饲料质量差的问题[6],北美和瑞典运动马存在能量饲料类型选择的相关代谢异常问题[7-8],国内运动马的饲养管理也存在很多问题,本综述对运动马的能量饲料营养相关代谢问题进行综述,并结合当前研究状况提出合理的优化供给策略。

1 粗饲料和谷物类饲料的消化吸收特性及其优缺点

要保证运动马的竞技性能和竞技水平,首要考虑的就是保证运动马的体能,需要在饲粮中供给充足的能量,运动马的能量来源包括粗饲料中的纤维素、木质素等结构性多糖以及谷物类饲料中的淀粉、饲粮中的油脂及蛋白质(通过糖异生作用供能),其中最主要的是纤维素和淀粉,对纤维素和淀粉的消化吸收特性及优缺点分析有利于我们针对性的优化运动马的能量供给方案。

作为一种草食性动物,马在长期进化作用下形成了适于粗饲料消化吸收利用的胃肠和营养代谢系统。粗饲料经马匹摄入后主要依赖于后肠道微生物发酵作用将纤维素等结构性多糖转化为挥发性脂肪酸,挥发性脂肪酸由肠道吸收入体经循环系统转运至肝脏进行糖异生,发挥供能作用[5],所以,肠道微生物稳态是保持马匹肠道功能和健康的主要因素。而肠道微生物相关研究指出宿主营养结构可直接影响肠道菌群多糖利用位点的组成结构,并影响肠道菌群稳态[9-11],进而可影响动物的健康状况,高纤维饲粮可促进纤维降解菌(多为益生菌,如假黄单胞菌、甲烷菌等)在马后肠道的增殖,对应的肠道菌群结构状况符合马匹的健康需求[12],而且高纤维素饲粮消化代谢产物有利于改善马匹的代谢健康。总之,高纤维饲喂模式是一种可改善运动马健康和福利的喂养方式。所以需保证马匹的粗饲料摄入量,但粗饲料的饱腹感强、消化速度慢且消化吸收效率相对较低,在挥发性脂肪酸吸收后的糖异生过程中还需要消耗部分能量。粗饲料是一种低营养浓度、低效率的饲料类型,不能完全满足运动马的能量需求,所以在运动马饲粮中需通过添加谷物类饲料进行营养补充。

淀粉等非结构性多糖的消化主要依赖于马内源糖消化酶的催化作用,马的内源糖消化酶包括双糖酶、蔗糖酶、乳糖酶和麦芽糖酶等,这些消化酶沿着肠道呈现不同的表达丰度特性,主要表达于前肠段,葡萄糖转运蛋白的表达也有一致的空间表达特性,D-葡萄糖由马肠道黏膜上的Na+/葡萄糖共转运蛋白1(SGLT1)转运入体,此转运蛋白在转录和翻译水平的表达丰度均表现为十二指肠>空肠>回肠[13],这就说明淀粉的消化及其产物葡萄糖的吸收均主要发生于马的前肠道。另外,淀粉等非结构性多糖的消化终产物为葡萄糖,葡萄糖吸收入体后可直接参与马匹的骨骼肌供能和糖原积累,所以谷物类饲料的能量浓度和利用率均较高。运动马在消耗肌糖原后补充速度慢,而剧烈运动后饲喂谷物类饲粮可加速其骨骼肌葡萄糖补充速度,提高其肌糖原补充速度[14],而且高淀粉饲粮可以提高运动马的最高心率,优化其反应性和运动能力[15]。但高淀粉饲粮会引致马的肠道菌群结构变化,提高盲肠和结肠中总厌氧菌、纤维素分解菌、淀粉菌和乳酸利用菌的比例,影响肠道菌群和黏膜免疫稳态,引发肠道炎症、胃肠绞痛等胃肠健康问题[16]。草食性动物在正常情况下的血液中葡萄糖浓度较低,而高淀粉饲粮经马匹消化吸收后可迅速提高血液中葡萄糖和胰岛素浓度,进而引致马代谢综合征等病理问题[17],而且高淀粉饲粮的摄食速度快,往往伴随规癖行为(crib-biting,CB),对运动马心理状况也有不利影响[18]。所以,德国马营养标准相关综述指出需调整运动马的营养供给模式,限制运动马的淀粉摄入量,并保证运动马的最低粗饲料摄入量,这有助于改善马匹消化系统的健康状况,并减少与营养有关的病理风险[19]。总之,运动马的能量供给需平衡粗饲料和谷物类饲料的供给量,并采用针对性的营养调控策略优化运动马竞技性能。

2 运动马能量供给的几个优化策略

粗饲料和谷物类饲料是运动马的主要能量来源,粗饲料的能量密度且生物利用率均处于较低水平,不能满足运动马能量需求;谷物类饲料可满足运动马能量需求,但可引致多种健康问题。Coenen等[19]对运动马粗饲料和谷物类饲料的能量、蛋白质含量及生物利用率进行了分析,提出马匹每日淀粉摄入量小于2 g/kg BW,每日粗饲料摄入量大于20 g/kg BW,才能保证马匹健康,但以这样的饲粮配比方式并不能完全满足高水平运动马的能量需求,所以应采用多种针对性优化策略改善运动马的能量营养状态,主要调控方式包括采用适宜的饲料加工工艺、谷物类饲料替代、添加非营养性饲料添加剂和优化饲草给料方式。

2.1 饲料加工工艺对运动马粗饲料消化吸收效率的影响

采用适宜的饲料加工工艺可改变马饲粮的物理和化学特性,从而优化马的膳食结构、采食频率、采食量及饲料消化利用率,进而改善马的生产性能和运动能力[20]。就谷物类饲料而言,研究显示采用热处理、化学处理及种皮破坏处理可改善马匹对谷物类饲料(玉米和大麦)干物质、淀粉、蛋白质和脂肪酸的盲肠消化率[21]。而运动马能量饲料供给更多的需关注其粗饲料的加工和贮存工艺选择,首先,饲草的刈割时间可影响饲草的营养组成和摄入时间,由于成熟后期饲草的纤维素和木质素含量较高,所以马匹的摄入时间长,咀嚼和吞咽速度慢,可有效减少马匹的CB[22],但成熟前期刈割饲草可提高其消化利用率[23]。另外,对于放牧马匹,通过刈割降低草皮高度,可有效降低放牧马匹饲粮中的非结构性多糖、水溶性多糖及乙醇可溶性多糖的含量,可有效防治马匹的胰岛素抵抗问题[24]

干草是马匹粗饲料的一个主要组成部分,在其生长和晒制干燥过程中的环境状况(空气雾霾及过敏原)会影响干草中的粉尘、霉菌和空气变应原含量,进而会引致马的呼吸道损伤问题[25]。选取适宜的干草调制手段,如干仓蒸制和浸泡[26],可有效降低干草中的呼吸性颗粒和微生物含量,且对干草中的非纤维多糖、粗蛋白质和矿物质等营养素含量无不利影响[27],有利于保证舍饲马粗饲料的卫生和清洁[28-29]。另外,干草的切割状况同样可影响运动马的采食和肠道生理特性。研究结果显示运动马需要咀嚼性纤维,相比于颗粒状草丸,完整干草可显著提高运动马的采食欲望、咀嚼次数及粪便pH,并缩短其站立时间,有利于维持其健康状况[30]

除晒制干草外,饲草的贮藏加工方式还有青贮、窖藏加工等。就营养素而言,相比于干草,窖藏半干草的粗蛋白质含量和总能较高,其他营养物质的保存质量良好,基本与干草一致[31];就营养素消化利用率而言,Moore-Colyer等[32]的研究发现,窖藏加工和青贮可显著提高饲用牧草的生物利用效率,相比于干草,青贮和窖藏加工可显著改善饲草的消化能、非淀粉多糖消化率及粗蛋白质消化率。但贮藏天数会影响窖藏青干草质量,随着贮藏天数的增加,饲草中淀粉酶活性和乙醇含量均有所下降,窖藏半干草在贮存之前是否切割可影响马的进食行为和粪便特性,切割窖藏半干草饲喂马匹的咀嚼率高而咀嚼次数较低,其粪便乙酸含量有所下降,pH有所升高[33]

综合以上的内容,运动马饲草最好采用窖藏半干草,饲喂完整饲草以提高其摄食时间并优化运动马肠道微环境,减少其CB,而饲喂干草时最好采用蒸制或浸泡处理以减少干草中的呼吸性颗粒和霉菌等致病因子,以期优化运动马呼吸道健康。

2.2 谷物类饲料替代对运动马健康状况的优化作用

运动马的高精料饲喂模式往往伴随肠道炎症、高血糖、胰岛素抵抗、过度肥胖等健康问题,进而引致马代谢综合征[34-35],会严重影响马匹健康和竞技水平。研究发现,运动马每天饲喂2.25 kg以上的干草可有效缓解高淀粉饲粮导致的肠道酸中毒和代谢问题,从而改善运动马的健康状况[36]。高纤维饲料可有效抑制马代谢综合征症状,基于运动马的消化系统功能特性,需要保证运动马一定的饲草供给量,同时选用更加健康的高能饲料原料替代运动马饲粮中的谷物类饲料原料,从而改善运动马健康状况。

优质粗饲料是谷物类饲料替代的第一选择,苜蓿干草在不同季节的可消化能及可消化粗蛋白质含量均很高,可满足高营养需求马匹如运动马、妊娠期与哺乳期母马的营养需求[37],可部分替代谷物类饲料。并且,研究发现,在饲粮中添加16%紫花苜蓿可显著提高马胃和粪便中结构性多糖利用菌如纤维素分解菌、木聚糖分解菌、乳酸利用细菌等的比例,改善马匹的消化道菌群结构[38],有利于抑制高谷物饲粮导致的消化道菌群失衡,优化其肠道健康状况。优质粗饲料的另一特性为高粗蛋白质含量,Essén-Gustavsson等[39]的研究指出高蛋白质优质粗饲料还可提高运动马的肌糖原和亮氨酸浓度,饲喂高蛋白质饲草的运动马在剧烈运动后短期内肌肉支链氨基酸浓度仍维持较高水平,这就意味着高蛋白质优质粗饲料有利于运动马剧烈运动后的肌肉恢复,而且适当提高饲粮中粗蛋白质含量可改善饲粮营养物质的消化率和沉积量[40-41]。总之,优质粗饲料的营养密度和消化吸收率均处于较高水平,可在满足运动马营养需求的同时改善运动马代谢和肠道健康状况,所以优质粗饲料可部分替代谷物类饲料。

其他饲料原料如油脂、甜菜浆、大豆皮等也是谷物类饲料的优质替代品。油脂的能量高、易吸收,且热增耗低,Williams等[42]发现用高脂肪和高纤维素饲粮代替高淀粉饲粮可有效降低母马哺乳期血浆中葡萄糖和胰岛素浓度,从而减缓母马哺乳期的消化和代谢紊乱问题,说明在高纤维饲粮中添加油脂是一种谷物类饲料替代的有效措施。甜菜替代谷物类饲料的可行性研究显示甜菜的可溶性纤维含量高,并可及时补充运动马能量[43],而且在干草中添加甜菜浆后马匹血浆中葡萄糖和胰岛素浓度均未出现显著提升[44],说明甜菜浆有潜力取代淀粉作为运动马饲料的能量来源。大豆皮是一种高能量纤维饲料,在马饲粮中采用大豆皮替代高达40%的精料补充剂可显著提高可发酵碳水化合物消化率,并且不会引致血浆中葡萄糖浓度的显著升高[45-46]。运动马的谷物类饲料替代就是在改变其饲粮能量相关营养组分的同时保证能量供给量,优质粗饲料、油脂、甜菜浆、大豆皮均可满足这一需求,且这些谷物类饲料替代品均可有效抑制谷物类饲料诱导的肠道菌群失衡,从而改善运动马的肠道和代谢健康状态。

2.3 非营养性饲料添加剂对运动马能量饲料代谢功能的改善作用

运动马肠道菌群结构是决定其消化道代谢健康的主要因素,通过外源添加益生菌、纤维素酶等饲料添加剂可影响马肠道菌群结构,调节其饲粮发酵过程和降解效率,可在一定程度上改善马匹健康状况。酿酒酵母是草食动物饲养中常用的益生菌,在高纤维饲粮中添加酿酒酵母可改善马的干物质、有机质及纤维素(中性洗涤纤维和酸性洗涤纤维)表观消化率,显著提高马对高纤维饲粮的生物利用率[47-48],而且补充活酵母菌可减少马匹胃内淀粉降解菌的数量,从而减少胃内淀粉降解比例[49],优化胃壁健康状况。除酵母菌外,Elghandour等[50]的研究显示,在饲粮中添加香肠乳杆菌可改善马后肠道高纤维饲粮如燕麦秸秆的消化率,提高甲烷、二氧化碳气体的产量。针对高淀粉饲粮,可通过外源添加埃氏巨型球菌降低马盲肠中乳酸的积累,稳定马匹盲肠pH,并增强其盲肠微生物发酵活性[51]。总之,益生菌可直接影响肠道菌群结构,提高马匹的纤维素或淀粉利用率,改善运动马的能量饲料利用效率。

运动马肠道中纤维素降解主要依赖微生物发酵作用,通过外源添加纤维素酶可改善饲喂高纤维饲粮马匹的干草(燕麦秸秆)摄入量和养分消化率,并可提高血液总蛋白浓度,优化马的饲粮利用效率和营养状况[52],进而更好地满足运动马的能力需求,减少谷物类饲料在饲粮中的比例。总之,非营养性饲料添加剂如酿酒酵母、乳杆菌等益生菌及纤维素酶均可改善马匹对能量饲料的利用效率,改善其能量代谢功能状态。

2.4 饲草给料方式对运动马健康状况的有利影响

运动马的饲养管理是影响运动马竞技性能和心理健康的一个重要因素,尤其是高谷物饲粮的摄入速度快,往往会伴随高频率CB;而粗饲料的摄量大且摄入速度慢,摄食时间延长,可有效控制运动马的CB[53]。饲草给料方式可影响马的采食行为和饲喂率。在饲喂成年马时,干草网可显著降低饲喂率,延长马的采食时间[54],而且小网眼或多层干草网供给干草时可在不改变马匹采食量的前提下,有效延长马匹的咀嚼时间,减少CB[55-57]。另外,也有研究采用新型的慢速进料器进行干草饲喂,亦可改善马匹行为状况[58],是一种有效的福利设备。总之,通过采用干草网、给料器等改变饲草的给料方式可有效延长马匹摄食时间,减少运动马CB。

3 小结

运动马的能量饲料供给需充分考虑粗饲料和谷物类饲料的平衡使用,既要保证运动马获得充足的能量,又要保证其健康状况。我们结合近几年运动马相关营养和饲养管理相关研究内容,提出几点运动马能量供给的优化方案,首先需采用适宜的加工贮存工艺如窖藏等优化粗饲料的生物利用率,在此前提上保证运动马的饲草质量,建议采用干草网、小型给料器等设备将优质牧草如紫花苜蓿等喂给运动马,在此基础上,可适度降低运动马饲粮中的谷物类饲料比例;还可在运动马饲粮中添加油脂、甜菜浆、大豆皮等来替代部分谷物类饲料,也可较好地应对谷物类饲料引致的代谢问题;另外,益生菌和外源纤维素酶等非营养性饲料添加剂也可在一定程度上改善马匹的能量利用效率及健康状况。但运动马的饲粮配合及能量代谢研究尚处于较低水平,还需综合考虑以上几个方面并结合运动马的发育阶段差异性,针对运动马各年龄段提出合理的能量供给模式,并按照优化策略调整后运动马的肠道菌群结构和相关代谢指标变化调整饲粮结构,以期获得高竞技水平的运动马,并改善其健康状况。

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