青藏高原牦牛被动食土及其矿物元素补充的应用基础研究

Soil ingestion was an important pathway for grazing animals to obtain and supplement mineral elements, and the involuntary soil ingestion was a significant resource compared with voluntary soil licks. The involuntary ingestion of soil was also found a major way for yak to ingest soil in our former research, and which has changed mineral elements constitute in daily ration of yak. Consequently, for better understood of its occurrence regularity, affecting factors, and potentional effects on yak nutrition, the preparing project will be conducted to study involuntary soil ingestion of yak through our former research achievement of salt or salt block supplement to prevent voluntary soil licks. However, endogenous markers technology of titanium (Ti) will be taken to determine the precision content of soil ingestion by yak simultaneously. The variable regularity of passive soil ingestion of yak grazing on pasture from different seasons, vegetation forms, herbage height, coverage, stocking rate et al. will be studied, and to reveal the relationship between involuntary soil ingestion and grazing pasture characterization factors, and further more to discuss its ecological characteristic. In addition, evaluation of the potential effect of involuntary soil ingestion on ration mineral nutrition structure of yak and their mineral nutrition profile will also be conducted through calculating soil ingestion content and mineral elements analysis in soil, forage, and body tissue of yak, and then to discuss elements content and proportion in minerals additives which balance mineral element requirement for grazing yak. Eventually, the practical experiment of mineral elements supplementation will be carried out from the above research to explore mineral additives trial-manufacture and management of supplementary feeding for grazing yak, and to improve mineral nutritional level of yak and their productivity.

食土是放牧家畜获取矿物元素的重要途径，被动食土是其重要来源。在我们前期对牦牛食土研究中发现被动食土是牦牛食土的主要方式，并严重影响牦牛日粮矿物营养结构组成。为进一步认识牦牛被动食土特征、影响因素及其潜在的营养学问题，本项目拟通过前期研究成果食盐/盐砖补饲解决牦牛主动舔食土的基础上，利用钛元素作为内标物测定牦牛被动食土量；研究牦牛被动食土量在不同季节、植被类型、牧草高度、盖度、载畜量等草地特征条件下的变化规律，揭示被动食土与放牧草地特征因子的关系，探讨牦牛被动食土的草地特征；通过研究被动食土量及土壤元素含量特征，结合牧草及牦牛矿物元素分析，科学评价被动食土对牦牛日粮矿物营养结构组成及其营养水平的影响，探讨调控补饲牦牛矿物添加剂中元素的含量及比例构成；基于上述研究成果，开展牦牛矿物元素补充的应用研究，探索放牧牦牛矿物元素添加剂的试制和补饲策略，提高放牧牦牛矿物营养和生产力水平。

被动食土是放牧家畜获取矿物元素的重要途径，其与草地植被、季节等因为有关。本项目重点研究牦牛食土量与草地植被特征关系，研究牧草黏附尘土的变化特征；开展牦牛舔砖补饲试验，为科学制定放牧牦牛矿物元素补充策略提供理论基础。此外，开展了不同食土水平对藏羊营养消化代谢和瘤胃细菌组成的影响。主要研究结果如下：.暖季草地植被盖度相对较高，但其高度和生物量均低于冷季；随着放牧试验的进行，草地主要特征因子均呈显著的下降趋势(P<0.01)，以冷季尤为明显。暖季牧草吸附尘土相对较低，试验前仅为1.12%；随着草地植被因子的下降尘土吸附量呈显著增加，其中，冷季尘土吸附量上升较快，试验第9天达5.89%。.牦牛百分食土量与草地生物量、针茅等盖度和高度呈显著负相关(P<0.01)，建立的暖季和冷季牦牛食土量估测模型分别为%SI=16.419+1.524 KHH -0.205 SCC+0.067 PVC- 0.225 KHC-0.032 TB（R2=0.996, P<0.01）和% SI=4.632+0.684 SCH-1.302 KCH-3.259 MRH+1.199 SCC +0.019 TB（R2=0.985, P<0.01）。.放牧后期牦牛血清中Na、K、Pi的含量上升， Cu、Fe、Zn、Ca 、Mg的含量发生下降，其中Fe的变化差异显著(P<0.05)，Ca、Cu含量低于临界水平；此外，后期牦牛瘤胃液中VFA的含量显著下降(P<0.01)。.补饲对牦牛的食土无显著影响（p>0.05），但补饲后血清元素水平均高于最低营养需求，无缺乏现象，补饲提高牦牛瘤胃液中VFA水平。.藏羊食土试验分析发现，10%食土水平可提高DM、EE、CP消化率，增重效果较好。5%食土水平组瘤胃液乙酸、丙酸及TVFA含量较高。拟杆菌门、厚壁菌门和纤维杆菌门是瘤胃细菌中的优势菌；NDFD、瘤胃液pH值与厚壁菌门下的瘤胃球菌呈显著正相关（P＜0.05），瘤胃液中挥发性脂肪酸浓度、NH3-N浓度与纤维杆菌呈显著正相关（P＜0.05）。.牦牛以被动食土为主，其中牧草吸附尘土是其重要来源；牦牛食土与草地生物量、主要牧草高度和盖度密切相关，可利用草地植被因子估算牦牛食土量；补饲矿物营养不影响牦牛食土，但可补充和平衡矿物营养；适当食土可提高放牧家畜营养消化代谢，这与其瘤胃微生物的变化组成有关。