尹国安,李想,刘洪贵
(1.黑龙江八一农垦大学动物科技学院,大庆163319;2.东北农业大学动物科技学院)
垫料(如秸秆、草壳、蘑菇料、锯末、泥土等)被认为是传统漏缝地板的替代,稻秸、麦秸等秸秆则是最常用的垫草,福利专家在评估猪的畜舍体系时多认为稻草等垫料的使用非常重要[1]。尽管报道,提供多种垫料时,猪更喜欢泥土、蘑菇料、木屑等垫料地面,而稻草仅优于水泥地面,但是稻草在实践中更容易获取,也更廉价[2]。秸秆的影响复杂且在很大程度上受品种、管理和畜舍影响[3]。垫草通常被认为可以提高猪的舒适性和福利[4],并可以减少氨气排放[5]。
猪大部分时间都在趴卧,趴卧时的充分舒适对它们的福利是重要的。垫草是一种合适的、有弹性的用于仔猪运动和休息的垫料,它能最大化地板接触面积,降低肢蹄负荷[3],猪还可以通过拱翻稻草调节趴卧区的微环境[6]。然而特定地板材料或垫料物质的选择取决于猪舍内的温热条件,猪在寒冷的环境喜欢躺在稻草上,而在高温时选择在裸露地面。而且,地板的最适温度也可能随猪的年龄或母猪的繁殖阶段而改变[3]。但是,除非温度较高时,与光秃秃的水泥地板相比,稻草对猪来说更受偏爱、更舒适。
垫草对畜舍卫生及健康的影响受畜舍及管理等多重因素的影响,因此为数不多的文献也相互矛盾。
通常认为垫草对畜舍卫生有不利影响并加重疾病传播,因为稻草增加猪接触粪尿污染物并被感染的几率,如耶尔森氏菌和食道口线虫[3]。Arey还发现垫草可能增加猪舍粉尘污染[4],但Scott等连续4年的研究没有发现粉尘浓度的显著差异,尽管和漏缝地板舍相比垫草舍育肥猪的呼吸系统疾病更多[7],可见垫草舍给猪的呼吸系统带来更大风险。
很多研究表明垫草系统可减少运动障碍[8-9]、肢蹄损害和其他腿部损伤[10-11],但其他研究并未发现垫草会减少皮肤损伤[12],还有试验显示垫料系统中严重脚伤更多[13]。Scott等的研究则显示不同地面条件下猪面临不同的足伤风险,在全漏缝地板舍中严重的足跟/足拓糜烂较多,而在垫草舍蹄指损伤更严重[7]。但是,垫草系统可以降低肢腿损伤造成的细菌感染、流感感染和胃肠道疾病的风险[7]。
可见,垫草和健康之间的关系并不确定,有些疾病/伤害在稻草舍更为普遍,而对其他疾病/伤害则是相反的[3]。
垫草对行为的影响主要是作为环境丰富物,很难找到像稻草一样有吸引力以长时间“娱乐”猪的玩具[3],而且垫草在趴卧时也可操控[14],增加了垫草的利用程度。另外,垫草也在一定程度满足猪的采食行为需求,并作为筑巢材料满足母猪的筑巢动机。同时,断乳后垫草环境能减少断乳混群争斗,但断乳前垫草环境会增加混群争斗[15]。
稻草是“拱咬和咀嚼的焦点”[6],因为大量研究[6-7,14-18]的研究结果表明,在贫瘠环境中猪的口吻部行为往往针对圈舍装置或同伴,而饲养在稻草上的猪更加活跃,花更多的时间跑动和转圈,拱翻和咀嚼稻草,并有更多游戏行为,异常行为减少。而且,垫草舍育肥猪的行为多样性较高[19]。厚垫草比流动稻草能提供更大的福利优势,因为针对稻草行为有随稻草提供量增加的趋势[4],但定期供应少量的稻草比厚垫草系统更具吸引力[20]。然而,秸秆和不良的社会行为的关系是复杂的,额外的空间提供或畜舍类型也可能有很大影响[3,21]。Andersen等还报道,对稳定的宽松群养母猪来说,提供稻草可能不是减少侵略的重要因素[10]。而且稻草和异常行为之间的关系因限饲水平不同而更复杂化,稻草对于限饲猪的攻击行为影响更大[22]。此外,数量有限的新鲜稻草的吸引力可能成为对有限的资源的攻击性竞争的诱因[23],利用稻草作为地面饲喂猪的垫料也显示会加重攻击的激烈程度[24]。
饲料及表达觅食行为受限制被认为是母猪口吻部规癖行为发生的主要原因,给母猪提供足够丰富的环境使他们能够表达觅食行为或减少母猪的采食动机可以防止这些规癖发生[25]。秸秆也可以成为限饲妊娠母猪重要的食物来源,不仅增加饱腹感,而且在撒地饲喂时处理和摄取食物的总时间也有所增加。已经证明提供大量的富纤维饲料能降低口吻部行为异常的频率同时增加休息时间[26],而同时提供稻草则可更好地避免口吻部规癖行为发生[27]。但稻草对采食动机的影响似乎微不足道,因为混合稻草的饲料没有阻止猪寻找食物[28],也没有充分减少自主采食量[29],王昕陟[30]也发现能量摄入是影响采食动机的主要因素,粗纤维作用较小。但是,Olsen认为即使有足够的稻草、空间和活动区,添加粗饲料也可以减少改向的口吻部行为[31]。另外,社会地位也可能极大地改变群养母猪稻草的有效性,因为占主导地位的母猪使用丰富物更多,从属母猪更不活跃,且在早晨非繁忙时间操控丰富物更多[32]。
秸秆对母猪的筑巢非常重要,怀孕母猪在产仔前一天有很强烈的稻草需求,并强烈喜好在垫草趴卧地产仔,但这取决于稻草供应量[3]。但是,在(半)自然环境母猪使用各种材料来筑巢,母猪在获得秸秆和树枝时筑的巢更好,而只有稻草可能不会引起足够的反馈,并使有些母猪长时间保持筑巢冲动,在产仔时更加不安[33]。在产仔/哺乳时,环境提供稻草对母猪的母性行为产生有利的影响:更多的哺乳期快速授乳哼叫、更多授乳后慢速哼叫、更多指向仔猪的发声和探察,对仔猪的求救发声更加敏感,在分离试验表现出更短的仔猪识别时间,但这种提高的母性行为对仔猪存活率没有稳定的作用[3]。
垫草舍母猪的日间皮质醇浓度在分娩前、分娩当日和哺乳28 d以上时均显著较低[34-36]。可见垫草对减少母猪的应激有一定作用,但以上研究多是与限位栏对比,所以其差异可能更多受限位环境影响。
有研究显示贫瘠畜舍的生长猪日间皮质醇升高[36],有的研究却没发现垫草舍对保育猪或生长猪皮质醇浓度的影响[36-38],这可能与环境处理时间短有关,因为长期使用木屑垫料也能降低母猪的昼夜皮质醇水平[39]。还有研究中垫草舍的生长猪的日间皮质醇浓度较高[37,40-41],可能是因为长期贫瘠环境使皮质醇昼夜节律不明显[37],也可能是HPA轴在持续应激时发生适应性变化,更不活跃[42]。另外,垫草舍还可以减少猪屠宰前应激,皮质醇浓度升高也较少[41]。通常认为长期处于应激状态对免疫系统有抑制作用,但垫草对免疫机能的影响没有确切的证据[36],De Groot等[40]对生长猪的研究中也仅发现白细胞淋巴细胞分化的微小差异,而Bolhuis等[43]的研究中垫草舍生长猪的体液免疫反应较弱,但受个体适应特性差异的影响。
垫草舍对生产性能的影响在研究结果中并不一致,大量研究表明在垫草舍饲养的生长育肥猪的采食量和日增重增加[8,14,23,44],并有更好的饲料转化率[44],但也有研究表明饲料转化率没有显著差异[8,45],而对保育猪的研究多显示垫草对生长速度和饲料转化率没有显著影响[11]。这可能与垫草作用时间有关,因为有研究显示短期(2~6周)提供稻草对育肥猪的生产性能没有显著影响[38]。Averós等[21]对大量研究结果的荟萃分析显示垫草有改善饲料转化率的微弱趋势。
垫草舍能提高猪的生产性能主要是因为垫草舍猪更多的活动导致的高采食量[8,23],其他可能因素包括增加的肠道容量、采食稻草带来的更多能量、秸秆使猪能够维持温热环境节省的能量[46]。但是,垫草作用因空间、地板类型、健康等的影响而不易确定[21,44],因为在一项控制其他环境因素的研究中没发现少量稻草对生长猪采食量、日增重、料重比的显著影响[36]。另外垫草作用还因猪个体适应特性的差异而影响[45]。
垫草对胴体重、背膘厚等胴体性能影响的不一致结果[8,13,16,41,44],则可能是增重差异导致的屠宰日龄的差异造成的。垫草还可能使猪肉系水力更高[41],并对肉的风味产生影响[47]。另外,垫草因为其可食入性,还可缓解低饲粮水平对群养母猪增重和背膘的影响[48]。
总之,垫草对猪福利的影响大部分是有益的。尽管其增加生产成本和特定疾病的风险,并带来管理上的不便,其仍是最可行的提高猪福利的途径,并有可能提高生产性能。
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