Zhanhuan Shang

Importance of Functional Ingredients in Yak Milk-Derived Food on Health of Tibetan Nomads Living Under High-Altitude Stress: A Review

Tibetan nomads have lived since ancient times in the unique and harsh environment of the Qinghai-Tibetan Plateau with average altitudes over 4000 m. These people have been able to live and multiply healthily over numerous generations under the extreme stress of high-altitude environment, including cold, hypoxia, and strong ultraviolet radiation, and with a simple diet devoid of vegetables and fruits for most of the year. Their survival depends heavily on yak milk, and its products comprise the main portion of their daily diet. In this review, yak milk and its derived products are examined in detail and compared with milk from other ruminant species. Yak milk products seem to be particularly rich in functional and bioactive components, which may play a role in maintaining the health status of Tibetan nomads. This includes particular profiles of amino acids and fatty acids, and high levels of antioxidant vitamins, specific enzymes, and bacteria with probiotic activity (yoghurt is the main food). Based on that, it is proposed that the Tibetan nomads have developed a nutritional mechanism adapted to cope with the specific challenges posed by the environment of the worlds highest plateau. Systematic studies are required to demonstrate this in a more mechanistic way.

Comparison of nitrogen utilization and urea kinetics between yaks ( Bos grunniens ) and indigenous cattle ( Bos taurus ) 1

Under traditional management on the Qinghai-Tibetan Plateau, yaks () graze only on natural pasture without supplements and are forced to cope with sparse forage of low N content, especially in winter. In contrast, indigenous Tibetan yellow cattle () require supplements during the cold season. We hypothesized that, in response to harsh conditions, yaks cope with low N intakes better than cattle. To test this hypothesis, a study of whole-body N retention and urea kinetics was conducted in 2 concurrent 4 × 4 Latin squares, with 1 square using yaks and 1 square using cattle. Four isocaloric forage-concentrate diets differing in N concentrations (10.3, 19.5, 28.5, and 37.6 g N/kg DM) were formulated, and by design, DMI were similar between species and across diets. Urea kinetics were determined with continuous intravenous infusion of NN urea for 104 h, and total urine and feces were concomitantly collected. Urea production, urea recycling to the gut, and ruminal microbial protein synthesis all linearly increased ( < 0.001) with increasing dietary N in both yaks and cattle. Urinary N excretion was less ( = 0.04) and N retention was greater ( = 0.01) in yaks than in cattle. Urea production was greater in yaks than in cattle at the 3 lowest N diets but greater in cattle than in yaks at the highest N diet (species × diet, < 0.02). Urea N recycled to the gut ( < 0.001), recycled urea N captured by ruminal bacteria ( < 0.001), and ruminal microbial protein production ( = 0.05) were greater in yaks than in cattle. No more than 12% of urea recycling was through saliva, with no difference between species ( = 0.61). Glomerular filtration rate was lower ( = 0.05) in yaks than in cattle. The higher urea recycling and greater capture of recycled urea by ruminal microbes in yaks than in cattle suggest that yaks use mechanisms to utilize dietary N more efficiently than cattle, which may partially explain the better survival of yaks than cattle when fed low-N diets.

Trolox equivalent antioxidant capacities and fatty acids profile of 18 alpine plants available as forage for yaks on the Qinghai-Tibetan Plateau

Traditionally, yaks (Poephagus grunniens) raised on the Qinghai-Tibetan plateau graze only natural pasture and much of their diet consists of sedges, in particular Kobresia spp. These ruminants are subjected to an extremely harsh environment of strong UV radiation, hypoxia and severe cold, which can lead to high oxidative stress. Consequently, it was predicted that sedges would contain high concentrations of functional antioxidants when compared with other alpine plants, and that this would help them survive the harsh conditions. To test the prediction, 18 alpine plants on the Qinghai-Tibetan plateau, which are available to yaks as forage, were examined. These plants, including four sedges, five grasses, five forbs and four shrubs, were analysed for gross constituents, Trolox equivalent antioxidant capacity, phenol content, and fatty acids composition. Based on their Trolox equivalent antioxidant capacity, the 18 plants were divided into three groups: low, medium and high. Three of the four sedges were ranked in the medium group and one in the low group, whereas three of four shrubs were ranked in the high group. The total phenol content of the plants ranged between 1.1 and 12.4 g gallic acid equivalents per 100 g DM, with the shrubs containing the highest concentrations. The prediction that sedges would contain higher antioxidant capacity than other alpine plants was not supported. It was concluded that other factors such as anti-nutritional contents and biomass availability are also important in determining dietary selection in yaks.

Recruitment of seedlings versus ramets as affected by pasture degradation in alpine meadows and the implications for ecological restoration

Background: The degradation of alpine meadows on the Qinghai-Tibetan Plateau (QTP) has an impact on vegetation recruitment from seedlings and ramets. Aims: Understanding the relative contribution of recruitment by seedling and ramet in alpine meadows is for the ecological restoration of degraded grasslands on the QTP. Methods: An experiment was conducted to investigate seedling and ramet densities, species composition and their relationships with standing vegetation in plots representative of non-degraded (ND), lightly (LD), moderately (MD) and severely degraded (SD) alpine meadows. Results: With increasing degradation and the reduction in vegetation cover, the number of seedlings and ramets declined. The proportion of young plants arising from seedlings was low, with the majority of species reproducing clonally. The establishment of seedlings of forbs in SD meadows led to species-rich, forb-dominant vegetation in these areas. Conclusions: LD and MD meadows appear to be able to be managed by reduced grazing for the restoration of grass- and sedge-dominated pastures. In contrast, restoration of SD meadows will require additional intervention, such as of seeding and weed eradication.

Inhibitory action of allelochemicals from Artemisia nanschanica to control Pedicularis kansuensis, an annual weed of alpine grasslands

The inhibitory action of allelochemicals can be used effectively for biological weed management and can minimise environmental impacts related to herbicides. The aim of the present study was to identify allelochemicals of Artemisia nanschanica Krasch, a typical weed with strong allelopathic effects, that could potentially control Pedicularis kansuensis Maxim, the key pioneer weed that causes rapid degradation of alpine pastures. Gas chromatography and mass spectrometry were used to identify the compounds of six extracts from A. nanschanica. Two ethyl acetate extracts were the most effective in reducing the seed germination rate and in inhibiting seedling shoot and root growth of P. kansuensis. Three chemical compounds from the ethyl acetate extracts were identified for their allelopathic inhibitory effects, a sesquiterpene and two aromadendrene oxides, with the sesquiterpene being the most effective. The three compounds showed the best inhibitory effect through synergistic action. We concluded that the three allelochemicals of A. nanschanica, either alone or in combination, can be used to biologically control P. kansuensis in alpine pastures on the Tibetan plateau.

Trolox-equivalent antioxidant capacity and composition of five alpine plant species growing at different elevations on the Qinghai–Tibetan Plateau

Background: Alpine plants on the Qinghai–Tibetan Plateau are exposed to an extremely harsh environment, namely severe cold, strong ultraviolet radiation, hypoxia and low CO2 partial pressure. These conditions are sources of oxidative stress, which increase in severity with increasing elevation. Aims: To examine whether antioxidant capacity and chemical composition of alpine plants change with increasing elevation. Methods: We measured the Trolox-equivalent antioxidant capacity (TEAC) and chemical composition of five alpine plant species at 3016, 3814 and 4621 m a.s.l. Results: With increasing elevation: (1) the TEAC increased and total phenols and tannins tended to increase in two forb and two shrub species but not in a sedge species; (2) concentrations of protein and fat increased in all five plant species; (3) polyunsaturated fatty acids (PUFA) increased and (4) mineral concentrations tended to decrease, but trends were inconsistent. Conclusions: We conclude that with increasing elevation, TEAC and total phenols and tannins increased which we interpreted as an adaptation to higher oxidative stress; and protein and fat contents increased to support high metabolic activity. The increase in PUFA and the trend for minerals to decrease with increasing elevation require further investigation.