三江源区不同季节放牧草场天然牧草营养价值评定及载畜量研究

摘要

为探究三江源区不同季节放牧草场天然牧草营养供给潜力和载畜量，选用3头安装永久性瘤胃瘘管的成年大通牦牛为瘤胃液供体动物，采用概略养分分析法和体外产气法，结合产草量对放牧草场牧草进行综合评定并确定其载畜量。结果表明，1）夏、秋及冬春放牧草场的可食风干草的最高产量分别为（123．83±17．88），（256．88±29．90）和（246．83±66．73）g／m2。2）夏、秋及冬春草场天然牧草的最高粗蛋白（CP）含量分别为（12．69±0．13）％，（10．54±1．22）％和（8．65±0．64）％，其含量随牧草生长而逐渐降低；夏、秋及冬春草场天然牧草 EE 的最高含量分别为（2．95±0．10）％，（4．38±0．17）％及（3．74±0．70）％；NDS 含量的变化趋势与 CP 一致，而 NDF 和 ADF 含量的变化与 CP 相反，随牧草生长含量不断增加。3）体外发酵 pH 和氨氮浓度均在正常范围内；夏季草场牧草的48 h产气量、24 h 产气估测消化能（DM）、代谢能（ME）和有机物质降解率（OMD）的最大值分别为（57．50±4．27）mL、（9．32±0．59）MJ／kg、（7．98±0．62）MJ／kg 和（57．93±3．23）％；秋季草场牧草分别为（54．67±5．35）mL、（8．83±0．64）MJ／kg、（7．47±0．68）MJ／kg 及（55．26±3．52）％；冬春草场牧草分别为（58．83±4．51）mL、（9．56±0．60）MJ／kg、（8．24±0．63）MJ／kg 及（52．69±5．14）％。4）无补饲条件下，夏、秋及冬春天然放牧草场载畜量分别按数量载畜量、数量载畜量和 DCP 载畜量核算放牧科学，其最适载畜量分别为7．05，19．51和2．47 SU／hm2；有良好补饲情况下，夏、秋及冬春天然放牧草场载畜量按 DCP 载畜量、ME 载畜量和 ME 载畜量核算放牧科学，其最适载畜量分别为14．85，29．00和5．03 SU／hm2。因此，三江源区牧草产量和品质季节性差异大，能－氮不平衡，通过补饲可以使夏、秋及冬春放牧草场的载畜量分别提高1．1，0．5和1．0倍左右，有利于促进当地畜牧业发展和生态保护。%To explore seasonal variations in the potential nutrient supply and carrying capacity of grazing pas-tures in the Three-River Source Region,three adult Datong yaks equipped the permanent rumen fistula were chosen to provide rumen fluid.Analysis of this fluid was combined with measurement of grass yield to compre-hensively determine the pastures’carrying capacity and gas production,using general nutrient analysis and in vitro techniques.The results showed that the maximum yields of edible dry grass in summer,autumn,winter and spring were (123.83±17.88),(256.88±29.90)and (246.83±66.73)g/m2 respectively.Maximum crude protein (CP)contents were (12.69±0.13)%,(10.54±1.22)% and (8.65 ±0.64)%,the contents gradually decreasing with grass growth.The maximum ether extract (EE)contents in summer,autumn,winter and spring were (2.95±0.10)%,(4.38±0.17)% and (3.74±0.70)% respectively.The change trend in neutral detergent soluble (NDS)content was consistent with CP,while neutral detergent fibre (NDF)and acid deter-gent fibre (ADF)contents varied negatively with CP.The pH value and NH 3-N concentration of solutions fer-mented in vitro were within normal ranges.The maxima of 48 h gas production and digestible energy (DE), metabolizable energy (ME)and organic matter degradation rate (OMD)(estimated by 24 h gas production)for summer pastures were (57.50 ± 4.27 )mL,(9.32 ± 0.59 )MJ/kg,(7.98 ± 0.62 )MJ/kg and (57.93 ± 3.23)%;for autumn pastures (54.67±5.35)mL,(8.83±0.64)MJ/kg,(7.47±0.68)MJ/kg and (55.26± 3.52)%;for winter and spring pastures (58.83±4.51)mL,(9.56±0.60)MJ/kg,(8.24±0.63)MJ/kg and (52.69 ± 5.14 )%.Without the provision of concentrates,according to grass and digestible crude protein (DCP)production results,the optimal yak carrying capacity of summer,autumn and winter and spring pas-tures was 7.05,19.51 and 2.47 SU/ha respectively.When supplementary concentrates were fed,maximum carrying capacity for the three seasons can reach to 14.85,29.00 and 5.03 SU/ha (based on DCP production for summer pastures and ME production for autumn,winter and spring pastures).In conclusion,the forage yield and quality of grazing pastures varies significantly by season.By supplementary feeding,carrying capacity in summer,autumn,winter and spring can be increased by 1.1,0.5 and 1.0 times,a result that would help to promote both local animal husbandry and ecological sustainability.