D. Shikui, L. Ruijun, P. Xiaopeng and H. Zizhi
Department of Grassland, Gansu Agricultural University, Lanzhou 730070, Gansu, P.R. China
The distributions of alpine shrubs on Qinghai-Tibetan Plateau of China are reviewed, and the relationship between the alpine shrubs and yak is discussed. Based on the nutritional evaluation and economic analysis, the utilisation of shrubs as protein supplements for the yak grazing on the alpine meadow is proposed.
Keywords: Grazing, protein supplement, shrubs, yak
In alpine pastoral areas, legumes are very limited in pastures. As a result, protein deficiency is one of the major constraints to the improvement of productivity of grazing livestock in these areas, i.e. for yak and sheep (Li and Song 1984). Previous studies have shown that supplementation of grazing yak and Tibetan sheep with protein-rich feeds can significantly improve their body condition and performances (Zhang et al. 1999). From ecological and economic points of view, due to the high protein content, nutritive value and availability, shrubs are likely to be the best protein supplements for yak grazing on the alpine meadow (Long et al. 1999, unpublished). Although a lot of researches on using of shrubs as protein supplements for grazing animals have been done in tropical and sub-tropical conditions (Everist 1969; Akkasaeng et al. 1989; Goodchild 1990; Raghavan 1990; Rajaguru 1990; Smith 1992; Topps 1992; Bonsi 1995; Robert 1997), there is very little information on evaluation of alpine shrubs as supplement feeds for grazing yak. This article reviews information available on this subject and concludes that more attention should be paid to the role of shrubs as an alternative protein feed source on the Qinghai-Tibetan Plateau.
Shrub is a kind of plant combining the characteristics of tree and grass. Shrubs have been defined as the leaves, shoots and sprouts, including tender twigs and stems of woody plants, which are cropped to a varying extent by domestic and wild animals (Robert 1997). Alpine shrub is an important type of vegetation, which almost covers the whole transition areas from forest to alpine meadow on the Qinghai-Tibetan Plateau in China, where the altitude varies from 3000 to 5000 metres above sea level (masl), with a total area of about 116,400 km2 located in the north-eastern Plateau, including the south-eastern Qinghai Province, the north-western Sichuan Province, western Gannan Prefecture of Gansu Province and the north-eastern Tibetan Autonomous Region (Wu 1980).
In the eastern part of these areas, i.e. the north-eastern Sichuan Province, the western Gannan Prefecture and the south-eastern Qinghai Province, the shrub land occupies the shadow slopes of the mountains between 3800 and 4200 masl at the elevation. The major species of alpine shrubs are generally Dasiphora fruticosa, Salix alpina, Sibiraea angustata, Spiraea alpina, Rhododendron capitatum, R. przewalskii and R. anthogonoides. Moreover, Dasiphora fruticosa, Caragana jubata and C. microphylla can be found occasionally on the sunny slopes of the mountains.
In the western part of the areas, i.e. the north-eastern Tibetan Autonomous Region, the alpine shrubs grow on the higher altitude lands, normally above 4000 masl, where the Dasiphora fruticosa extensively covers the sunny slopes while the Caragana jubata and C. microphylla occupy the shadowed slopes. Rhododendron capitatum and Salix alpina occasionally also appear on the shadowed parts of the mountains.
The distribution of alpine shrubs is quite similar to the distribution of the yak (Table 1). The great overlap of the distribution between the shrubs and the yak shows that the shrubs play an important role in yak farming system on Qinghai-Tibetan Plateau of China.
Table 1. Distribution of alpine shrubs and the overlap with that of yak.
Species |
Distribution |
Overlap with yak distribution |
Dasiphora fruticosa |
Along north-eastern Qinghai-Tibetan Plateau |
+++ |
Salix alpina |
East and west parts of north-eastern Qinghai-Tibetan Plateau |
++ |
Sibiraea angustata |
East part of north-eastern Qinghai-Tibetan Plateau |
+ |
Spiraea alpina |
East and west parts of north-eastern Qinghai-Tibetan Plateau |
++ |
Rhododendron capitatum |
South-eastern Qinghai Province and Gannan Prefecture |
+ |
R. przewalskii |
South-eastern Qinghai Province and Gannan Prefecture |
+ |
R. Anthogonoides |
Occasionally found on some parts of north-eastern Qinghai-Tibetan Plateau |
+ |
Caragana jubata |
West parts of north-eastern Qinghai-Tibetan Plateau |
++ |
C. Microphylla |
Occasionally found on some parts of north-eastern Qinghai-Tibetan Plateau |
+ |
| + = much; ++ = very much; +++ = extremely much. | ||
Alpine shrub lands are the habitat and grazing lands for the yak in summer and sometimes in the winter as well. As such, they play an essential role in yak production (Long et al. 1993; Zhou et al. 1994; Yu et al. 1999; Zhang et al. 1999). There is substantial interaction between the alpine shrubs and the grazing yak on Qinghai-Tibetan Plateau. The effect of this interaction depends a lot on the grazing strategy.
Under appropriate grazing strategy, the moderate activity of the animals can promote the re-growth of the shrubs; therefore, the total phenological biomass and the quality of shrubs are enhanced because of more leaves and tender stems. In turn, the better nutrient supply from shrubs can increase the intake, digestibility and metabolism by the animal; thus the animals' performances are improved. However, inappropriate grazing strategy can destroy the balance of soil-plant-animal ecosystem, with important implications for the shrub growth and animal production. With high grazing intensity, all of the foliage and tender stems of shrubs are eaten by the animals, which result in the disappearance of some shrubs, the destroyed community structure of plant, and the lowered yield of herbage in the sward. Eventually the animal production is badly reduced and the serious problem of soil erosion creeps in (Zhou et al. 1994). On the other hand, if the grazing intensity is too low, the re-growth of shrubs cannot be stimulated efficiently, and the productive potential of plants cannot be achieved. Thus, animal productivity can be considerably affected by the imbalance in both nutrient supply and feed deficiency.
Clearly, the harmony between the alpine shrubs and the grazing yak is very important in this ecosystem. Shrub-yak integration must be maintained to optimise the productivity of the yak production system.
At present, on the Qinghai-Tibetan Plateau, most Tibetan yak herders adopt a seasonal rotational grazing system, under which they divide the pastures into summer and winter grazing lands. The winter grazing lands are herb lands, which are reserved with fence and mainly utilised in cold and dry season (from November to April) when forage availability becomes low. The summer grazing lands are shrub lands, the communal areas in which the yak can graze in wet and warm season (from June to October). When the yak are herded on the shrub lands in the wet season, they browse the foliage and tender stems of shrubs together with grazing the grass under and around the shrubs. In this way, the animals are able to get sufficient feeds with better-balanced nutrients (Long 1999).
For the grazing animals, the benefits from shrub (browse) feeds include increased metabolism energy intake, increased nitrogen intake, feed efficiency, improved palatability, increased availability of minerals and vitamins, improved rumen function, better animal performance and a laxative influence on the alimentary system (Robert 1997). An important attendant advantage is a lowered cost of feeding because energy and protein supplements do not have to be purchased. The herdsmen's experiences also suggest that the yak cows graze on shrub lands during reproductive period show higher heat rate. With regard to the soil-grass-animal ecosystem, the benefits of feeding shrubs to animals are mainly decreased grazing pressure on the grasslands, reduced overgrazing rate and retarded degradation of the grasslands, and, in the long run, the balance in the ecosystem is maintained gradually, and the feed resources are utilised sustainably.
In yak framing system on Qinghai-Tibetan Plateau, shrubs possess multiple roles. They can be used as the fuel by the nomadic herders in summer when they travel a long distance from their houses to herd their animals on the shrub lands. They are also used as the fence materials by the herders to protect the winter grazing lands and to make enclosures or shelters for the animals at night. Moreover, some herders use the shrubs as construction materials to make the shelters for the animals in winter.
All considered, the shrubs are much more important as protein supplements for the yak grazing on the grass meadow. Grassland scientists or animal nutritionists ignored this point, and only limited literatures on the values of the shrubs as animal feeds are available in this region, even in the whole country. Therefore, the importance of shrubs as supplementary feeds for yak has to be emphasised in terms of their nutritive value and economical benefit in animal production.
The nutritive value of forages depends on the voluntary intake of the feed consumed and the quantity of dry matter and, in turn, the dry matter content in terms of dietary energy, proteins, minerals and vitamins. Ultimately, much will depend on the actual quantity of feed eaten by the animal on a daily basis (Robert 1997). With shrubs, the quantity eaten by the yak is relatively small. When compared with herbs, the acceptance or edibility (palatability) of shrubs is much lower, partly due to the physical characteristics (hairiness, bulkiness), and partly because of the presence of compounds, which may affect taste and appetite (volatile oils, soluble carbohydrates and anti-nutritional factors). However, the shrubs do considerably contribute to the compositions of daily diets of grazing yak. Pu (1999) reported that on the Dasiphora fruticosa shrub lands, shrubs account for 19.2% of diets of yak. Other researchers have also provided evidences that indicate some alpine shrubs form major components of diets of grazing yak (Long et al. 1993; Zhou et al. 1994; Yu et al. 1999; Zhang et al. 1999).
Although information about the digestibility (degradability) of nutrients in shrubs are not available, the results from chemical analysis on the compositions of some shrubs can provide us clues on the quality of shrubs as animal feeds. Available information shows that the CP, NFE, Ca, P and ME in alpine shrubs are quite high, even higher than those of the major native herbages (Table 2). It is clear that shrubs have a distinct advantage over alpine grasses and sedges due to their superior nutritional values. Some non-legume shrubs such as Hippophae tibetica and Myrimanica germanica are comparable to the legume herbages; some legume shrubs such as Caragana jubata, C. microphylla and C. pygmaea are excellent alternatives to the legume herbages. Therefore, from a nutritional point of view, shrubs can be the protein supplements for grazing yak on alpine grass meadow.
As has been alluded to, one of the major beneficial effects of shrubs as supplement feeds for grazing yak is the lowered cost of feeding compared to a system in which feed supplements are purchased. The overall goal is to improve animal productivity based, as much as possible, on locally available resources with a minimum cost.
Table 2. Chemical compositions of foliage and stem of some alpine shrubs and major herbages on the Qinghai-Tibetan Plateau (dry matter (DM) basis).
Species |
DM |
CP |
NFE |
CF |
Ash |
Ca |
P |
ME |
Shrubs |
||||||||
Caragana jubata |
91.48 |
10.72 |
39.31 |
28.81 |
9.15 |
1.67 |
0.133 |
8.91 |
C. microphylla |
92.95 |
12.51 |
41.21 |
28.63 |
7.67 |
1.29 |
0.116 |
9.24 |
C. pygmaea |
90.07 |
21.75 |
42.16 |
24.76 |
7.82 |
1.16 |
0.47 |
9.841 |
Dasiphora fruticosa |
91.70 |
10.38 |
47.84 |
24.76 |
6.66 |
0.99 |
0.134 |
9.21 |
D. giabra |
92.06 |
9.69 |
46.15 |
28.12 |
6.25 |
1.27 |
0.119 |
9.12 |
Spiraea alpina |
91.66 |
10.46 |
47.74 |
26.68 |
4.39 |
0.91 |
0.086 |
9.46 |
Hippophae tibetica |
91.96 |
23.64 |
47.11 |
12.98 |
3.76 |
0.90 |
0.304 |
10.60 |
Myrimanica germanica |
91.15 |
12.01 |
48.70 |
12.01 |
18.11 |
4.15 |
0.127 |
8.49 |
Grasses |
||||||||
Elymus nutans |
90.29 |
8.47 |
36.09 |
37.03 |
6.65 |
0.33 |
0.129 |
7.60 |
Poa pratensis |
92.56 |
6.88 |
50.80 |
27.94 |
5.60 |
0.28 |
0.11 |
9.11 |
Roegneria Nutans |
88.68 |
6.47 |
36.99 |
37.95 |
5.43 |
0.22 |
0.202 |
8.70 |
Stipa aliena |
86.86 |
10.18 |
34.82 |
32.86 |
5.63 |
0.45 |
0.185 |
8.15 |
Agropyron cristatum |
91.37 |
9.40 |
27.20 |
43.40 |
10.97 |
0.26 |
0.20 |
6.42 |
Sedges |
||||||||
Carex kansuensis |
92.81 |
8.56 |
53.18 |
23.07 |
5.81 |
0.55 |
0.094 |
9.37 |
Kobresia capillifolia |
85.93 |
11.56 |
36.40 |
30.47 |
5.96 |
0.59 |
0.118 |
9.31 |
| DM = dry matter; CP = crude protein; NFE
= nitrogen free extract; CF = crude fibre; Ca = calcium; P = phosphorus; ME =
metabolic energy.
Sources: Jia (1987); Chen (1994). |
||||||||
On the Qinghai-Tibetan Plateau, as free-ranging animals, the yak graze on the natural grasslands whole year round, and they cannot get sufficient protein from natural herbage (Long 1995). However, it is hard for these animals to obtain protein and energy supplements from outside the system due to the remoteness, poor infrastructure, financial limitation and labour deficiency in the yak farming areas. Fortunately, the yak can freely browse the protein-rich shrubs without extra financial input at anytime of the year. Therefore, from an economic point of view, it is feasible to develop shrubs as protein feeds in yak farming system.
Although shrubs are ideal protein supplements for the grazing yak as far as nutritive values and economic benefits are concerned, some potentially dangerous compounds (anti-nutritional factors) have been found in some of these fodder shrubs. Tannins are the most important ones in alpine shrubs (Long 1999). It is, therefore, necessary to carry out more research to determine appropriate methods of alleviating these deleterious effects in order to upgrade the quality of protein of these feeds. For optimum utilisation of shrubs, it is essential that details of agronomic characteristics, palatability and nutritive values of the important species are determined through both chemical analysis and in sacco and in vitro methods.
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