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

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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 world's highest plateau. Systematic studies are required to demonstrate this in a more mechanistic way.
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Importance of Functional Ingredients in Yak Milk-
Derived Food on Health of Tibetan Nomads Living
Under High-Altitude Stress: A Review
Xusheng Guo a b , Ruijun Long a b c , Michael Kreuzer d , Luming Ding a b , Zhanhuan Shang a c
, Ying Zhang a c , Yang Yang a c & Guangxin Cui a c
a International Centre for Tibetan Plateau Ecosystem Management; Lanzhou University ,
Lanzhou , 730000 , P.R. China
b State Key Laboratory of Grassland and Agro-Ecosystems, School of Life Sciences, Lanzhou
University , Lanzhou , 730000 , P.R. China
c State Key Laboratory of Grassland and Agro-Ecosystems, School of Pastoral Agriculture
Science and Technology, Lanzhou University , Lanzhou , 730000 , P.R. China
d ETH Zurich, Institute of Agricultural Sciences, Universitaetsstrasse , 2 , 8092 Zurich ,
Switzerland
Accepted author version posted online: 21 Aug 2012.Published online: 04 Nov 2013.
To cite this article: Xusheng Guo , Ruijun Long , Michael Kreuzer , Luming Ding , Zhanhuan Shang , Ying Zhang ,
Yang Yang & Guangxin Cui (2014) Importance of Functional Ingredients in Yak Milk-Derived Food on Health of Tibetan
Nomads Living Under High-Altitude Stress: A Review, Critical Reviews in Food Science and Nutrition, 54:3, 292-302, DOI:
10.1080/10408398.2011.584134
To link to this article: http://dx.doi.org/10.1080/10408398.2011.584134
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DOI: 10.1080/10408398.2011.584134
Importance of Functional Ingredients
in Yak Milk-Derived Food on Health
of Tibetan Nomads Living Under
High-Altitude Stress: A Review
XUSHENG GUO,1,2 RUIJUN LONG,1,2,3 MICHAEL KREUZER,4
LUMING DING,1,2 ZHANHUAN SHANG,1,3 YING ZHANG,1,3 YANG YANG,1,3
and GUANGXIN CUI1,3
1International Centre for Tibetan Plateau Ecosystem Management; Lanzhou University, Lanzhou 730000, P.R. China
2State Key Laboratory of Grassland and Agro-Ecosystems, School of Life Sciences, Lanzhou University,
Lanzhou 730000, P.R. China
3State Key Laboratory of Grassland and Agro-Ecosystems, School of Pastoral Agriculture Science and Technology,
Lanzhou University, Lanzhou 730000, P.R. China
4ETH Zurich, Institute of Agricultural Sciences, Universitaetsstrasse 2, 8092 Zurich, Switzerland
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 world’s highest plateau. Systematic studies are required to
demonstrate this in a more mechanistic way.
Keywords Yak milk, bioactive components, high altitude, oxidative stress, nutritional adaption, hypoxia
INTRODUCTION
Tibetan nomads are renowned for having made a living on
‘the roof of the world’, the Qinghai-Tibetan Plateau, by raising
yaks (Bos grunniens) since ancient times. Archaeological
evidence indicates human occupation of the Tibetan plateau as
early as 25,000 to 50,000 years ago (An, 1982) which is earlier
than any other high-altitude population (Aldenderfer, 1999).
Tibetans could therefore represent the population most adapted
to hypoxic conditions. Yaks, domesticated 8000–12,000 years
ago (Guo, 2006), fulfill an important function in the Tibetans’
Address correspondence to Ruijun Long, Xusheng Guo, Lanzhou
University, Lanzhou 730000, P.R. China. E-mail: longrj@lzu.edu.cn;
guoxusheng 78@163.com
life and in developing the prosperity of the people in the vast
mountainous regions, where no other agricultural activities
exist. Tibetan nomads use yaks for various purposes as they
provide milk, meat, transportation, and fur and hide for clothing
and shelter, as well as dried dung for fuel (Wiener, 2002).
Still the main production purpose is milk (Dong et al., 2003).
Although the global milk production from yak is insignificant
compared with that produced by dairy cattle and other rumi-
nants, it contributes 15% to Chinese milk consumption (Long,
1994) and is preferentially consumed by the Tibetan nomads
(Beall and Goldstein, 1993).
It has been reported that metabolic adaptation to heat,
cold, and high-altitude exposure may, in some instances, be
accompanied by changes in nutrient requirements (Simon-
Schnass, 1992). Energy expenditure, and vitamin and mineral
292
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IMPORTANCE OF YAK MILK-DERIVED FOOD FOR HEALTH OF TIBETAN NOMADS 293
requirements are increased under all three environmental condi-
tions; moreover, dietary antioxidants are considered beneficial
to reduce the increased oxidative stress associated with cold
and high-altitude environments [hypoxia and ultraviolet (UV)
radiation] (Askew, 1995; Owen and Johns, 2002). The body’s
metabolic response to cold and hypoxia can be either augmented
by proper nutrition or impaired by inadequate nutrition (Askew,
1994). The composition of the diet of Tibetan nomads is usually
quite simple. Besides baked Tibetan barley meal (known locally
as Zanba), yak milk and milk products comprise the main
portion of Tibetan pastoralists’ daily food intake (Beall and
Goldstein, 1993), and have been major sources of nutrients
for Tibetan nomads for centuries. It was reported that Tibetan
nomads do not consume vegetables or fruits for almost eight
months of the year, or even throughout the year, yet they show
no obvious signs of vitamin or mineral deficiency (Goldstein
and Beall, 1987). This raises the question of how Tibetans are
able to maintain their health under these extremely stressful
conditions while consuming a diet of such a simple composition.
It is likely that yak dairy products have played a vital role in
maintaining the health of Tibetans in this hypoxic environment.
The aims of this review are, therefore, to describe the unique
characteristics of the chemical and biochemical properties of
yak milk-derived food compared with milk from other ruminant
species and to provide evidence that the daily consumption of
substantial amounts of yak dairy products plays a vital role
in maintaining the health of Tibetan nomads. Furthermore, the
possible mechanisms by which these food items may contribute
to the adaptation of the nomads are discussed.
HEALTH CHALLENGES CAUSED BY THE HARSH
ENVIRONMENT OF THE TIBETAN PLATEAU
It is well know that the unique stress at the high altitude of
Tibetan Plateaus is hypobaric hypoxia caused by the decrease
in barometric pressure with increasing altitude and reduction
in atmospheric oxygen concentration (Beall, 2006). Hypobaric
hypoxia becomes progressively more severe with increased alti-
tude and stresses biological systems due to the impeded supply
of oxygen required for metabolism in the mitochondria. Nor-
mally, living in an environment with hypoxia and, additionally,
strong UV radiation causes changes to the cellular metabolism of
organisms (Aldashev et al., 2005), and the abnormal metabolism
found in histocytes is caused by metabolic disorders due to the
increase in oxygen free radicals in the organisms.
Jefferson et al. (2004) reported that one of the main rea-
sons for the suffering from oxidative stress by high-altitude
residents is that the exposure to high altitude could weaken en-
zymatic and nonenzymatic antioxidant systems. Dosek et al.
(2007) described that long-term exposure to high altitude, with
the associated decrease in oxygen pressure, can result in ox-
idative/reductive stress, enhanced generation of reactive oxygen
and nitrogen species, and related oxidative damage to lipids, pro-
teins, and DNA. The severity of this metabolic challenge is re-
lated to the degree of altitude. Oxidative stress is one of the main
causative factors for some common diseases experienced by
high-altitude residents, such as premature senility, high-altitude
brain edema, high-altitude pulmonary edema, and high-altitude
erythrocytosis (Beckman et al., 1990), and is also considered to
be associated with other diseases such as atherosclerosis (Ursini
et al., 1998), carcinogenesis (Gasche et al., 2001), neurodegen-
erative diseases (Beal, 1995), coronary heart disease (CHD),
stroke, and rheumatoid arthritis (Negri et al., 1991; Keli et al.,
1996). Environmental factors such as hypoxia and exposure to
UV light and cold together aggravate the above-mentioned dis-
eases (Askew, 2002). The increased UV radiation experienced
at high altitude is responsible also for other challenges (Simon-
Schnass, 1994, 1996), which can result in eye damage and skin
cancer. Although the Tibetan nomads are usually dressed with
a minimum of skin exposure, their faces and hands are mostly
exposed. As suggested by Fuchs and Packer (1991), UV-B and
UV-A rays have enough energy to penetrate the dermis and even
subcutaneous tissues.
LONG-TERM METABOLIC ADAPTION STRATEGIES
OF INHABITANTS OF THE TIBETAN PLATEAU
Despite the constraints outlined above, the ethnic group of the
Tibetan seems to have survived quite healthily on the world’s
highest plateau for numerous generations. This suggests that
they have developed some unique adaptive mechanisms. The
Tibetans rarely suffer from high-altitude sickness, and their eye-
sight and skin remain mostly uninjured. There is evidence for
genetic adaptation (Simonson et al., 2010) as well as unique
features of heart and pulmonary circulation in healthy Tibetan
nomads compared with people living at sea level (B¨
artsch and
Gibbs, 2007; Penaloza and Stella, 2007). Compared with the lat-
ter, Tibetans have greater arterial oxygen saturation at rest and
during exercise, and show less loss of aerobic performance with
increasing altitude (Wu and Kayser, 2006). The Tibetan people
also have a greater hypoxic and hypercapnic ventilatory respon-
siveness, larger lungs, and a greater lung diffusing capacity;
moreover, their arterial oxygen and blood hemoglobin concen-
tration is lower than in lowland inhabitants and high Andean
populations living at similar altitudes (Ge et al., 1994; Beall
et al., 1998; Beall, 2006, 2007). It was also reported that Ti-
betans develop only minimal hypoxic pulmonary hypertension
and have higher levels of exhaled nitric oxide than lowlanders or
high-altitude Andeans dwellers (Wu and Kayser, 2006). Several
of the above findings are even occurring in Tibetans born at low
altitude when exposed for the first time to high-altitude once
adult (Wu and Kayser, 2006).
A proteomics study suggested that Tibetans at high altitude
are protected from tissue damage induced by reactive oxygen
species and possess a specific metabolic adaptation (Gelfi et al.,
2004). Zhang et al. (2000) found that activities of superox-
ide dismutase in erythrocytes and glutathione peroxidase in
plasma and plasma concentrations of vitamins E and C were
significantly higher in native Tibetans than in migrants of Han
Chinese (Hans) to the Tibetan Plateau. Conversely, hematocrit
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294 X. GUO ET AL.
Tab l e 1 Comparison of concentrations of blood plasma variables in Tibetan
and migrated Hans living at 4300 m altitudea
Variable Tibetans Hans p-valueb
Haematocrit (%) 51.1 58.2 <0.001
Superoxide dismutase activity in red blood
cells (units/g hemoglobin)
12,731 11,571 <0.001
Malondialdehyde (μmol/L) 4.42 5.10 <0.05
Glutathione peroxidase activity (units) 137 126 <0.001
Vitamin C (μg/mL) 21.9 21.0 <0.05
Vitamin E (μg/mL) 8.55 7.77 <0.01
aData taken from Zhang et al. (2000).
bSignificance was declared at p<0.05.
and plasma malondialdehyde were significantly lower in Ti-
betans than in Hans (Table 1). The total serum lipid profile
of Tibetans would suggest a thrombogenic pattern with high
proportions of palmitic acid and stearic acid and a low propor-
tion of linoleic acid (Fujimoto et al., 1989), but findings with
regard to serum phospholipids did not support this hypothe-
sis (Pieroni and Price, 2006). Further, Owen and Johns (2002)
showed that the Tibetans’ serum profiles are characterized by
higher high-density lipoprotein (HDL) and lower serum total
cholesterol, apolipoprotein B, and lipoprotein levels compared
with populations from Japan (Fujimoto et al., 1989), Korea,
China, Belgium, and Nigeria (Kesteloot et al., 1990; Cobbaert
and Kesteloot, 1992). This indicates the presence of a type of
lipid metabolism defense mechanism against the development
of atherosclerosis (Fujimoto et al., 1989), which is supported
by the result from an epidemiological study comparing elderly
Tibetans and Hans living either at the same altitude or in the
lowlands (Yang et al., 2008). Accordingly, the prevalence of
hypertriglyceridemia (5.0%) and low HDL cholesterol (3.1%)
of Tibetans was lower than that found in Hans living in Tibet
(22.5% and 10.7%, respectively) and in Beijing (14.7% and
8.4%, respectively; Yang et al., 2008).
These findings indicate that eating behavior must be criti-
cally important in mitigating high-altitude stress. There must
also be a substantial consumption of dietary antioxidants to
abate the altitude-induced oxidative challenges. Fruits and veg-
etables rich in antioxidant compounds would be very helpful in
this respect (Owen and Johns, 2002; Hung et al., 2004; Naka-
mura et al., 2008), but are not commonly available in the diet of
the Tibetan nomads. Instead, the dietary strategy of these people
relies heavily on consumption of yak milk and milk products,
with the associated high dietary fat intake. Such high intakes of
fat might be considered detrimental to human health; however,
Givens (2010) suggests that humans who consume large quan-
tities of milk and dairy products are actually at a slightly lower
risk of developing cardiovascular disease (CVD) than those who
consume few of these foods.
There are many reports of dietary compounds conferring spe-
cific benefits to human health. For instance, reindeer milk plays
an important role in maintaining the health of the Lapps from
the polar region due to its high nutrient density. Reindeer milk
contains more than 20% fat, three times more protein, double
the mineral content, and more ascorbic acid than cow’s milk
(Haraldson, 1983). The cuisine in many countries around the
Mediterranean contains considerable amounts of fish, seafood,
and olive oil, which are rich in n-3 fatty acids (FA), and fruits
and vegetables high in antioxidants, and is thought to prevent
or reduce the risk of CHD (de Lorgeril et al., 1994; Bach-Faig
et al., 2011). The Greenland Inuits have lower serum triaclycerol
(TAG) concentrations compared with the Danish population de-
spite high intakes of dietary fat, because this fat is especially
rich in n-3 (omega-3) FA (Dyerberg and Bang, 1982; Bjerre-
gaard et al., 1997). Elevated TAG concentrations are associated
with an increased risk of CDH (Assmann et al., 1998; Sarwar
et al., 2007).
An adaptive behavior to cope with high-altitude oxidative
stress has been reported for some native highland tribes in India
who often eat the seeds of Trichopus zeylanicus, which contain
bioactive components with antioxidant capacity derived from
polyphenols and sulfhydyl. Consumption of these seeds has
been shown to scavenge free radicals and reduce the levels of
lipid peroxidation and DNA damage (Tharakan et al., 2005;
Dosek et al., 2007).
PROCESSING OF YAK MILK AND THE CONSUMPTION
OF YAK MILK PRODUCTS BY THE TIBETAN NOMADS
According to Dong et al. (2003), the nutritionally dense and
sweet yak milk is greatly liked by Tibetans. Most fresh yak
milk is processed immediately by households into a variety of
indigenous products capable of being stored for a considerable
time under the climatic conditions of the Qinghai-Tibetan
Plateau. Products include milk, butter, cream, yoghurt, and
Qula (Table 2). Nondairy foods include Zanba, made from
the baked highland barley meal, occasionally supplemented by
consuming Tibetan sheep and yak meat. Yak milk and butter are
usually mixed with tea and drunk by the nomads every day. Qula
is a kind of dried curd, made by adding whey to skimmed milk,
followed by sun drying of the curd. Qula is consumed as a snack
by herdsmen when tending their grazing animals, together with
milk and tea or is mixed with butter and barley meal to make
Zanba (Cai, 1992). Among all yak milk products, yoghurt is
the most important and is of considerable economic and dietary
importance to the people of the Qinghai-Tibetan Plateau (Cao
et al., 2004; Zhang et al., 2008). Yoghurt is consumed by the lo-
cals in amounts as high as 1 to 2 kg per day (Zhang et al., 2008).
Due to its limited shelf-life, yoghurt is more readily available
in the warm season (from June to September) when most milk
is being produced. During the cold season (from October to
May), other products serve as staple foods. Yak butter can
be stored for a long time without undergoing oxidation. This
is facilitated by the typically low temperature at the Tibetan
plateau. When yak butter is blended with vegetable oil, it is
possible to further extend its shelf-life (Neupaney et al., 2003a).
The generally long shelf-life is attributed to the rich content of
antioxidants in yak butter and because it is mainly composed of
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IMPORTANCE OF YAK MILK-DERIVED FOOD FOR HEALTH OF TIBETAN NOMADS 295
Tab l e 2 Daily consumption of yak milk and yak milk products by adult
Tibetan nomadsa
Milk Butter Qula Yoghurt
Daily intake 100–200 mL 50–100 g 30–80 g 1000–2000 g
Mode of
consumption
Drunk in tea,
3 to 8 times
daily
Drunk in tea,
3 to 5 times
daily
Drunk in tea
or eaten
with baked
barley meal
Drunk directly
aData from Zhang et al. (2008) and Yang et al. (2008), based on an extensive
household survey in Tibet and the Qinghai Province of China.
TAG (980 g/kg total lipids), few free sterols, and phospholipids
(3.2 and 2.7 g/kg, respectively), and insignificant amounts of
hydrocarbons and sterol esters (Neupaney et al., 2003a). Its
specific FA profile also makes yak butter harder (melting point
of 41Cvs.36
C of butter produced from cattle milk; Neupaney
et al., 2003b). Such properties have also facilitated its use in a
unique art from known as ‘yak butter-flower,’ which provides
a decorative exposition of Tibetan Buddhism and culture.
ROLE OF YAK DAIRY PRODUCTS IN COVERING DAILY
NUTRIENT REQUIREMENTS AND MAINTAINING
HEALTH OF THE NOMADS
There is evidence from the literature that yak milk has unique
properties that make it particularly useful in meeting the nutri-
tional requirements and sustaining the health of the Tibetan
nomads. It could be hypothesized that the particular composi-
tion of yak milk reflects the animals’ ability to survive at such
high altitudes with its nutritional stress during long cold winters.
The animals have responded by developing unique mechanisms
for accumulating metabolites, differing from those of other do-
mestic ruminants. In general, yak milk has a higher nutrient
density than milk from dairy cattle. Total milk solids, fat, and
protein concentrations are almost twofold higher than the levels
found in Holstein cattle, which are globally the most promi-
nent milk-producing genotype (Table 3). Compared with cattle
milk-based yoghurt, yoghurt made from yak milk is also richer
in these nutrients (Table 4). The daily consumption of 1 kg of
yak yoghurt provides 68% of the protein, 62.5% of the fat, 69%
of the potassium, and 38% of the zinc (Zhang et al., 2008) re-
quired to meet the Chinese Dietary Reference Intakes (DRIs)
for adults (Chinese Nutrition Society, 2000). The amount of cal-
cium, phosphorous, and magnesium consumed with this amount
of yak yoghurt would also meet the Chinese DRIs for each of
these elements.
Energy Supply
By consuming large amounts of yak milk and butter, Tibetan
nomads are able to derive sufficient energy to cope with elevated
requirements in high-altitude environment (Askew, 1995). Ti-
betan nomads, who generally consume yak butter, are known
to be very strong mountain climbers with fewer reported health
problems (Neupaney et al., 2003a).
Protein and Amino Acid Supply
Like in dairy cattle, the major protein in yak milk is casein,
accounting for over 60% of total proteins present (Sheng et al.,
2008). A recent study by Mao et al. (2007) suggested that there
were some active casein peptides in yak milk that exhibit an
inhibitory activity against the angiotensin-I-converting enzyme.
This would suggest that yak milk casein provides a natural anti-
hypertensive component, with potential future commercial value
in the field of functional foods. Sheng et al. (2008) reported that,
like in cattle milk protein, glutamic acid is the most abundant
amino acid in yak milk protein (Csap´
o-Kiss et al., 1995). This
amino acid is an important excitatory neurotransmitter and also
plays a vital role in the metabolism of sugars and fats (Garattini,
2000). Additionally, yak milk protein has a higher proportion
of total essential amino acid than cattle milk (464 vs. 432 g/kg
protein, respectively). Yak milk protein is especially richer in
methionine than that of dairy cows (31 vs. 18 g/kg protein,
respectively; Csap´
o-Kiss et al., 1995; Sheng et al., 2008). Me-
thionine breakdown products are known to act as endogenous
antioxidants by scavenging various oxidizing molecules (Levine
et al., 1996). Therefore, the extra methionine may increase the
antioxidant potential of the diet of the Tibetan nomads.
Saturated Fatty Acids
The saturated fatty acids (SFA) consumed with milk and
milk products are a matter of concern for human health. A high
consumption of especially the short- and medium-chain SFA is
considered to increase the risk of developing CVD (Nakamura
et al., 2003). Similar to milk fat of other ruminant species grazing
high alpine pastures (Bianchi et al., 2003; Zeppa et al., 2003;
Leiber et al., 2005), the proportion of these two classes of FA
is clearly lower in milk and milk products originating from yak
compared with products originating from more conventional
feeding systems (Tuo, 2006; Or-Rashid et al., 2008). The total
concentration of the SFA as a whole is also markedly lower in
yak milk fat than in other ruminants’ milk fat (Table 5). Similar
Tab l e 3 Comparison of composition of the milk from yak and Holstein cows (g/kg)
Total solids Fat Protein Lactose Ash Reference
Yak 157–184 55–86 42–64 33–58 4–9 Silk et al. (2006)
Holstein cattle 114–120 25–35 30–35 45–50 7 Bett et al. (2004); Martimez et al. (1991); Khorasani et al. (2001)
Downloaded by [ETH Zurich] at 23:44 04 November 2013
296 X. GUO ET AL.
Tab l e 4 Comparison of the composition of yoghurt prepared from yak and cattle milk (data from various sources)
Total solids Fat Protein Lactose Ash Energy Lactic acid bacteria Yeast (log Coliforms
(g/L) (g/L) (g/L) (g/L) (g/L) (MJ/kg) (log CFU/mL) CFU/mL) (MPN/100 mL)
Yaka143 53.7 54.4 23.4 8.6 4.21 9.18c8.33 20
Cowb123 27 25 63 8 3.01 6–8a3–6c<90d
aZhang et al. (2008).
bCited from Institute of Nutrition and Food Safety, Scientific Academy of China (1991).
cData quoted in Zhang et al. (2008)
dAccording to Guo (2003).
CFU =colony-forming units, MPN =most probable number.
results were also found in yak cheese and butter (Table 6).
However, because the Tibetans’ diet primarily consists of dairy
products and meat (Beall and Goldstein, 1993), these people
still are exposed to a higher thrombogenic risk than people
consuming less fat and including vegetable oils in their diet. As
the incidence of CVD is no greater than in other populations,
this risk factor seems to be reduced by other properties of yak
milk and milk products.
n-3 Fatty Acids
In general, the proportions of total polyunsaturated fatty acids
(PUFA), total unsaturated fatty acid (UFA), and the n-3/n-6 FA
ratio are higher in yak milk fat and its products than in milk fat
from cattle, sheep, and goats (Tables 5 and 6). Recent studies
have shown that yak milk and its products are particularly rich
in some biologically active FA. This list includes the n-3 FA,
especially 20:5 n-3 [EPA (eicosapentaenoic acid)] and 22:6 n-
3 [DHA (docosahexaenoic acid)], but also 18:3 n-3 (Table 6).
According to Du (2009), EPA and DHA account for 0.41%
versus 0.19% and 0.25 versus 0.03 g/kg total FA in yak and
cattle milk fat, respectively. Two authors report that 20:5 n-3
and 22:6 n-3 may even be absent in cattle milk (Yu et al., 2006;
Du, 2009). Compared with Canadian cheddar cheese, cheese
produced from yak’s milk in Nepal has an n-3/n-6 FA ratio that
is more than four times higher (0.87 vs. 0.20; Table 6). The ratio
is also much higher than that found in goat cheese, but similar
to sheep cheese. The content of n-3 PUFA in yak cheese lipids
is much higher than in that of cheddar cheese (3.2 times), sheep
cheese, and goat cheese (Table 6).
Reasons for these differences, apart from genotype effects,
may include high-altitude grazing as a factor, because cattle
Tab l e 5 Comparison of proportions of various groups of fatty acids in milk
fat of different ruminants (g/kg of total fat)
Livestock species SFA MUFA PUFA CLA Reference
Yak on pasture 675 281 44.3 21.7 Du (2009)
Cattle 744 232 24.2 10.8 Jahreis et al. (1999)
Ewe 731 230 38.5 10.8 Jahreis et al. (1999)
Goat on pasture 705 269 25.8 6.5 Jahreis et al. (1999)
Goat indoor 741 218 40.5 6.4 Jahreis et al. (1999)
SFA =saturated fatty acids, MUFA =monounsaturated fatty acids, PUFA =
polyunsaturated fatty acids, CLA =conjugated linoleic acids.
grazing in the Alps at about 2000 m altitude is reported to have
increased proportions of n-3 FA and n-3/n-6 FA ratio in their
milk (Bianchi et al., 2003; Kraft et al., 2003; Hauswirth et al.,
2004; Leiber et al., 2005). However, as this was mainly a result
of elevated 18:3 n-3 and not of 20:5 n-3 and 22:6 n-3 (Leiber
et al., 2005), a genetic influence specific for the yaks would
seem a more probable explanation.
High blood cholesterol level, particularly the low-density
lipoprotein (LDL) cholesterol, is a well-established risk factor
for CHD; HDL cholesterol concentrations are inversely asso-
ciated with this risk (Lunn and Theobald, 2006). High TAG
concentrations are also reported being closely related with an
increased risk of CHD (Austin, 1989; Assmann et al., 1998).
Several meta-analyses have demonstrated that monounsatu-
rated fatty acids (MUFA) and PUFA may reduce both total
serum cholesterol and LDL cholesterol, and increase serum
HDL cholesterol (Mensink and Katan 1992; Clarke et al. 1997;
Howell et al. 1997), thus reducing the risk of CHD (Lunn and
Theobald, 2006). Still n-3 FA and, especially, 20:5 n-3 and
22:6 n-3, are the most effective in that respect. Regular con-
sumption of sufficient amounts of 20:5 n-3 and 22:6 n-3 may
reduce the incidence of sudden death, myocardial infarction,
stroke, atherosclerosis, CHD, inflammatory diseases, and per-
haps even behavioral disorders (Connor, 2000; Harris et al.,
2008; Simopoulos, 2008; Riediger et al., 2009; Gogus and
Smith, 2010). The n-3 FA are essential for human health, and a
deficiency-related disease may occur when they are consumed
in quantities that are insufficient in relation to the n-6 FA. For
adults, the n-3/n-6 FA ratio should be at least 0.25 in fatty foods
(Simopoulos, 2002).
The particularly high ratio of n-3/n-6 of >0.8 reported in
milk from yaks and cows kept in the Alps may help to explain
the so-called ‘Alpine paradox,’ meaning the presence of a robust
cardiovascular health of alpine human populations despite a
high fat intake (Hauswirth et al., 2004). Accordingly, the high
ratio of n-3/n-6 FA and concentration of n-3 FA or other PUFA
habitually consumed with yak milk and its products by the
nomadic Tibetan people appear to play a vital role in maintaining
their health. As outlined above, Tibetans have a thrombogenic
serum lipid profile (Fujimoto et al., 1989), but other variables do
not support this risk factor (Pieroni and Price, 2006). It remains
to be explored whether the low CHD risk profile of Tibetans,
as compared with the Hans described earlier (Yang et al., 2008)
is the result of the consumption of the n-3 FA with yak milk
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IMPORTANCE OF YAK MILK-DERIVED FOOD FOR HEALTH OF TIBETAN NOMADS 297
Tab l e 6 Proportions of fatty acids and groups of fatty acids in cheese and butter from different ruminant species (g/kg of total fatty acids)
Yak Cattle (Bos taurus) Sheep Goat
Fatty acid CheeseaButterbCheeseaButtercCheesedButtereCheesef
n-3 PUFA 21 14 6.6 9.6 16 14 6.5
EPA 0.68 0.63 0.41 0.27
DHA 0.23 0.24 0.06 0.0
α-linolenic acid 17 8.3 4.9 8.6 16 6 6.5
Vaccenic acid 62 60 14 15 22 26 12
CLA 23 25 5.7 7.0 13.0 7.0 4.6
Linoleic acid 21 10 28 35 18 45 22
Arachidonic acid 1.2 1.3 1.5 3.6 2
SFA 595 627 651 682 684 662 728
MUFA 324 270 301 254 270 249 223
PUFA 45413765466940
n-3:n-6 PUFA 0.87 0.51 0.20 0.17 0.89 0.25 0.30
“–” indicates not detected.
aOr-Rashid et al. (2008).
bYu et al. (2006).
cBaer et al. (2001).
dAddis et al. (2005).
eZlatanos et al. (2002).
fLucas et al. (2008).
EPA =eicosapentaenoic acid, DHA =docosahexaenoic acid, CLA =conjugated linoleic acids, SFA =saturated fatty acids, MUFA =monounsaturated fatty
acids, PUFA =polyunsaturated fatty acids.
and its products, or a genetic adaptation or both where yak milk
might facilitate the expression of this favorable profile.
Conjugated Linoleic Acids
Extensive studies have demonstrated that conjugated linoleic
acids (CLA), especially the cis-9, trans-11-18:2 isomer (ru-
menic acid), can have anticarcinogenic and antidiabetic (Type
II) functions, and can improve bone mineralization, reduce body
fat accretion, retard the development of atherosclerosis, and
modulate the immune system (Belury, 2002; Barcel´
o-Coblijn
and Murphy, 2009; Benjamin and Spener, 2009). Oral admin-
istration of CLA to hypoxic rat was shown to significantly in-
crease serum nitric oxide synthase (Wei and Wei, 2004). This
enzyme catalyzes L-arginine to produce nitrous oxide, which is
an endogenous relaxation factor of blood vessels and can alle-
viate the damage to cells, improve microcirculation, and inhibit
lipid peroxidation, thereby preventing atherosclerotic lesions
(Christodoulides et al., 1995; Tan et al., 2000). Like the n-3
FA, CLA may reduce the risk of development of CVD as it re-
duces plasma TAG, total plasma cholesterol, LDL cholesterol,
and LDL/HDL-cholesterol ratio in animals (Lee et al., 1994; Ni-
colosi et al., 1997; Kritchevsky et al., 2000, 2002, 2004; Wilson
et al., 2000) and in humans (Noone et al., 2002; Tricon et al.,
2004).
Dairy products and foods derived from ruminants are the ma-
jor dietary source of CLA, especially rumenic acid, for humans
(Bauman and Lock, 2006). Rumenic acid is mainly formed in
the mammary gland of ruminants from trans-11-18:1 (vaccenic
acid), a ruminal biohydrogenation intermediate (Griinari et al.,
2000). However, also the conversion of vaccenic acid to ru-
menic acid in the human body could substantially increase the
metabolic supply of CLA. Therefore, ruminant-source food
that is rich in vaccenic acid is favorable as well. Accord-
ingly, biomedical studies with animal models have shown that
vaccenic acid has anticarcinogenic and antiatherogenic proper-
ties because it is converted to rumenic acid (Bauman and Lock,
2006).
Proportions of total CLA, rumenic acid, and vaccenic acid in
the fat of milk, butter, and cheese from yaks are at least twice as
high as those observed in cattle (Tables 5 and 6; Neupaney et al.,
2003a; Du, 2009). When comparing yak and Canadian cheddar
cheeses, it was shown that this ratio was 4.2:1 and 2.8:1 for total
CLA and total 18:1 trans-FA (Or-Rashid et al., 2008). Rumenic
acid makes up proportionately 0.9 of total CLA in yak butter
(Neupaney et al., 2003a; Or-Rashid et al., 2008). Thus, the daily
ingestion of yak milk-derived foods may also contribute to the
high-altitude tolerance of the Tibetan nomads as they are rich
sources of CLA and vaccenic acid.
Different from the n-3 FA, the CLA content in milk appears
to be promoted by feeding fresh and conserved grass as opposed
to maize silage and concentrates (Leiber et al., 2005). Again,
there may be a genotype effect, but also an effect caused by
specific plant species expressing activity inhibiting certain steps
of the ruminal biohydrogenation cascade. This was suspected
as the cause of the very unusually high levels of rumenic acid
found in two sheep species grazing mountainous pastures in
Bulgaria (Leiber et al., 2010).
Antioxidant Vitamins
Vitamins A, E, and C are known to be major antioxidants,
and assist in the elimination of free radicals. Vitamin A also
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298 X. GUO ET AL.
Tab l e 7 Comparison of average concentrations of vitamins with antioxidant
properties in milk products of yak and dairy cattlea
Vitamin A Vitamin E Vitamin C Reference
Milk Yak 408 μg 1009 μg 150 mg Chang (2007)
Cattle 302 μg 903 μg 7 mg Zhang et al. (2008)
Butter Yak 4.0 mg 28.3 mg Neupaney et al. (2003b)
Cattle 6.9 mg 23.4 mg Wang et al. (1999)
Yogurt Yak 51.6 mg 17.4 mg Zhang et al. (2008)
Cattle 24.2 mg 4.4 mg 10 mg
“–” indicates no data available in the literature.
aData are presented as per 1 kg of either milk or milk products from yaks and
cattle.
plays an important role in the maintenance of good eyesight.
Extensive research indicates that an increased intake of antiox-
idant vitamins, especially of vitamin E, is beneficial in alleviat-
ing altitude-induced oxidative damage (Simon-Schnass, 1992;
Askew, 1995; 2002; Schmidt et al., 2002; Dosek et al., 2007) and
diseases induced by reactive oxygen species (Negri et al., 1991;
Steinmetz and Potter, 1991; Keli et al., 1996). Oral supplemen-
tation of vitamin E (40 mg/day) in rats was found to reduce the
increase in lipid peroxidation induced by exposure to a hypoxic
environment equivalent to 7500 m of altitude (Ilavazhagan et al.,
2001).
The vitamins with antioxidant properties are present in
yak dairy products in higher concentrations than in the corre-
sponding dairy products from cattle (Table 7) (Neupaney et al.,
2003a; Chang, 2007). The DRIs of vitamins A, E, and C for
adults (Chinese Nutrition Society, 2000) are 2500 IU, 14 mg,
and 60 mg, respectively. From the data shown in Tables 2 and
7, it can be estimated that Tibetan adults can obtain sufficient
vitamin A and at least 50% of DRIs for vitamins E and C only
by the daily consumption of yak dairy products. Therefore,
despite the almost complete absence of vitamin intake from
vegetables during most of the year (Goldstein and Beall, 1987),
yak dairy products provide a valuable alternative source of
antioxidant vitamins, which explains why these people show
no obvious signs of vitamin deficiency.
Enzymes
A comparative study showed that the activity of some hy-
drolases and oxidoreductases, such as acid phosphatase, alka-
line phosphatase, lipase, catalase, and superoxide dismutase,
are much higher in yak milk than in milk from Holstein cows
(Tang, 2007). These enzymes could facilitate essential phys-
iological functions by eliminating excessive reactive oxygen
species (free radicals), which then do not exceed the levels tol-
erated in the bodies of high-altitude-dwelling Tibetans.
Probiotics and Undesired Germs
Consumption of yogurt is known to provide several health
benefits, mainly due to its cultures acting as probiotics. The
potential health effects of probiotic bacteria include blocking
gastroenteric pathogens, neutralizing food mutagens produced
in the colon, enhancing the immune response, lowering serum
cholesterol, preventing colon cancer and hepatic encephalopa-
thy, curing intestinal dysfunction and constipation, treating pep-
tic ulcers, and normalizing stool transit (Lee et al., 2009; Dicks
and Botes, 2010; Higashikawa et al., 2010).
The average count of lactic acid bacteria in yak yoghurt is
higher than that in yoghurt made from cattle milk (Table 4).
Therefore, it can be concluded that Tibetan nomadic people ac-
tually ingest large numbers of viable lactic acid bacteria with
their high daily portion of yoghurt, especially in summer. Lactic
acid bacteria, especially Lactobacillus spp. and Bifidobacterium
spp., are important intestinal tract residents and are used as pro-
biotic strains to improve health (Lee et al., 2009). Lactobacillus
fermentum (31%) and Lactobacillus casei (28%) are the pre-
dominant lactic acid bacteria species in traditionally fermented
yak yoghurt (Airidengcaicike et al., 2010).
As another group of potential probiotics, some yeast strains
can inhibit the growth of spoilage and pathogenic microorgan-
isms, and the combination of low pH produced by the bacterial
starter with the alcohol and CO2produced by the yeasts is also
inhibitory to many undesirable microorganisms (Ferreira and
Viljoen, 2003; Narvhus and Gadaga, 2003). Like lactic acid
bacteria, yeast numbers in yak yoghurt are higher than those in
cattle yoghurt (Zhang et al., 2008; Chen et al., 2009; Table 4).
Coliforms, microorganisms derived from fecal contamina-
tion or enteric pathogens, seem to be much lower in yak yoghurt
compared with cattle yoghurt (Table 4) and the maximum num-
ber recommended by the National Standard of People’s Repub-
lic of China for yoghurt (GB 2746-1999; Guo, 2003). This low
number of coliforms in yak yoghurt suggests that this food is
quite safe. Thus, the production of yak yoghurt presents a very
favorable and easy method of preservation.
Lactose Intolerance
Because of the high consumption of yak milk products, even
by the adults, the question arises whether lactose intolerance,
associated with diarrhea, is a problem in the Tibetan nomads.
Lactose from intensive milk consumption has also been pro-
posed as a possible risk factor for ischemic heart disease (Segall,
1994). This might be concluded from indirect metabolic evi-
dence, considering that calcium can increase fecal excretion of
lipids, and hence elicit a hypolipidemic effect, while this process
is counteracted by lactose, which facilitates calcium absorption
(Pieroni and Price, 2006). However, as unprocessed milk con-
stitutes only a relatively small proportion of total consumption,
it is not likely that this issue is of concern to Tibetans. Yoghurt
contains much less lactose, because it is fermented by lactic
acid bacteria (Pieroni and Price, 2006), and these bacteria can
further help to ferment the remaining lactose in the digestive
tract. Butter and cheese contain little or no lactose anyway, and
these foods show no correlation with CVD (Segall, 1994).
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IMPORTANCE OF YAK MILK-DERIVED FOOD FOR HEALTH OF TIBETAN NOMADS 299
Non-nutritional Functions
Yak milk and its products also have certain functions in the
life of the Tibetan nomads, other than nourishment. Yak butter
is believed to exhibit some unique physicochemical properties
different from milk fat of other mammals. Therefore, it is also
used as a natural medicine to heal wounds and provide relief
from body pains. In addition, the nomadic people use yak but-
ter to protect their skin from insect bites and the adhesion of
pathogenic bacteria. To investigate the possible medical benefits
of yak butter, a study was conducted to examine the tyrosinase
inhibition activity of this product (Neupaney et al., 2003b). The
results indicated that yak butter with its lactic acid, NaCl, citric
acid, and ascorbic acid showed pronounced tyrosinase inhibition
activity. Tibetan nomadic people live in a strong UV radiation
environment and local people state that they often use the yak
butter to protect their face and skin from sunburn or cold. The
benefits can probably be attributed to the biochemical pathway
by which the amino acid L-tyrosine in the yak butter is converted
to melanin by tyrosinase; melanin is a vital component of skin
and hair that facilitates pigment formation and protects the skin
from damage by UV rays (Neupaney et al., 2003b). However,
so far, relatively little is understood of the pharmaceutical role
that yak butter plays in the daily life of the local people.
CONCLUSIONS
The relative richness of nutritional and biologically active
ingredients in yak milk and its products, under the inhospitable
high-altitude environment, is an excellent example of how an in-
digenous diet may have enabled these nomads to adapt and live
healthily for thousands of years in the extreme environment of
the Qinghai-Tibetan Plateau. Although some research has been
conducted to investigate the multifunctionality of yak milk and
its products, systematic studies are still needed to demonstrate
the potential role of the functional ingredients in the foods de-
rived from yak milk on human health in a more mechanistic
way. The Tibetan nomads as managers of the plateau ecosystem
not only rely heavily on other biological components such as
microbial sources, vegetation, and animals, but have coexisted
and been interdependent on these foods for a very long time.
However, global warming and overgrazing in recent decades is
leading to a destabilization of the Tibetan ecosystem, which is a
potential risk to the simplicity of the Tibetan herders’ food chain
because of a reduction in both quantity and quality of yak milk.
That such changes may have an adverse impact on Tibetan no-
mads’ health, and possibly even the long-term survival of their
present system of pastoral agriculture, should also be the cause
for serious concern.
ACKNOWLEDGMENTS
This work was supported by grants from the National Nat-
ural Science Foundation of China (project number 31170378)
and the Program for New Century Excellent Talents in Univer-
sity (program number NCET-11-0209). The authors would like
to express their great appreciation to Mr Malcolm Gibb (for-
merly of the Institute of Grassland and Environment Research,
Aberystwyth, United Kingdom) for revision of the manuscript.
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... Yaks primarily inhabit the Qinghai-Tibet Plateau of China [1][2][3]. They are well-adapted to harsh environmental conditions such as low oxygen, low pressure, and extreme cold. ...
... In addition, yak milk is a natural product unique to the plateau, with high quality and high nutritional values. It is rich in functional and bioactive ingredients that are critical for antioxidation, regulation of the intestinal microflora, immune regulation, and anti-inflammation [1,[6][7][8][9]. Therefore, it highly caters to the expectations of consumers for high-quality dairy products. ...
... The MECs cultured in vitro demonstrated that MEC could secrete LEP and promote self-renewal upon LEP stimulation. A combination of prolactin (PRL) hormone and MEC improved the secretion of cow casein and promoted the proliferation of MECs [1,17]. ...
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... Residents of this area rely heavily on animal husbandry to financially support themselves. However, this area is characterized by strong ultraviolet radiation, low atmospheric O 2 partial pressure, and low temperatures throughout the year (Zha et al., 2016;Sun et al., 2021), which pose several challenges to animals in the region (Cheviron and Brumfield, 2012;Guo et al., 2014). Qiao et al. (2013a) reported that the production efficiency of dairy cows is lower in high-altitude areas than in low-altitude areas. ...
... Dairy products such as yogurt, dregs, and butter are a part of the daily diet of Tibetans and an indispensable part of their culture (Beall et al., 1996;Guo et al., 2014). Therefore, milk self-sufficiency in Tibet is highly desired and of importance to locals. ...
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The production efficiency of dairy cows is affected by altitude, with lower efficiency reported at higher altitudes. However, only a few studies have investigated the digestion performance, serum antioxidative characteristics, rumen fermentation performance, and rumen bacteria of Sanhe heifers at different altitudes. Therefore, in this study, we explored the effects of altitude on these aspects of Sanhe heifers. We evaluated the effects of altitude on the apparent digestibility of nutrients, serum antioxidative characteristics, rumen fermentation parameters, and rumen bacteria in Sanhe heifers. Twenty Sanhe heifers from the same herd and managed with the same practice were used. However, the heifers were from two regions in China: 10 were fed in Hulunbuir City, Inner Mongolia Autonomous Region (119°57′E, 47°17′N; approximately 700 m altitude, named LA) and 10 were fed in Lhasa City, Tibet Autonomous Region (91°06′E, 29°36′N; approximately 3,750 m altitude, named HA). The dry matter intake (DMI), average daily gain (ADG), and DMI/ADG ratio were higher (p < 0.05) in LA than in HA heifers, whereas the apparent total tract digestibility of dry matter, ether extract, and crude proteins were higher (p < 0.05) in the HA group. Compared with LA heifers, the HA heifers showed decreased (p < 0.05) serum concentrations of superoxide dismutase and glutathione peroxidase and increased serum concentration of hydrogen peroxide (p < 0.05). Altitude did not significantly affect the volatile fatty acid concentration in the rumen, but HA presented a lower acetate-to-propionate ratio than LA. The 16S rRNA gene sequencing data showed that altitude significantly affected the rumen microbial composition. At the phylum level, the HA heifers presented a lower relative abundance of Actinobacteria (p < 0.05) and higher relative abundance of Spirochaetae (p < 0.05) than the LA heifers. The correlation analysis revealed that the operational taxonomic units belonging to the genus Prevotella_1 were correlated (p < 0.05) with altitude and DMI. The results indicate that altitude can influence the apparent digestibility of nutrients, serum antioxidant capacity, rumen fermentation, and rumen bacteria composition of Sanhe heifers. The study provides insights into the adaptation mechanism of Sanhe heifers to high-altitude areas.
... The yak (Bos grunniens) is a mammal that lives at high altitudes. It is an important plateau animal that provides many human necessities [1,2]. However, yaks have a low reproduction rate [3,4]. ...
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... Наряду с коровьим молоком набирает обороты спрос на нетрадиционное молоко и получаемую из него продукцию [1][2][3]. По данным Национального статистического комитета Кыргызской Республики, на 2020 г. поголовье коров составляло 855,5 тыс., объемы производства сырого молока -1668 тыс. т. ...
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... Plateau (3,4). Therefore, yak has an irreplaceable economic status, which has an important impact on the development of the yak industry and the promotion of economic development in China (5). ...
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Yaks usually live in an extremely harsh natural environment resulting in low reproductive performance, so the production of yak cannot meet local demand in China. In order to solve this problem, the experiment aims to explore the effect of different feeding modes on the semen quality of male yaks, so as to provide a theoretical basis for improving the yield of yaks in Tibet. We used the combined analysis of metabolomics and microbial sequencing to explore the underlying mechanisms that affect the differences in semen quality between the house feeding (HF) system and the free range (FR). The results showed that the sperm motility ( P < 0.001) and sperm concentration ( P < 0.05) in the HF group were significantly higher than the FR group, and the abnormal sperm rate ( P < 0.01) in HF was significantly lower compared to FR. House feeding modes increased some beneficial materials in blood and testis especially some antioxidants, unsaturated fatty acids, and amino acids. House feeding group increased some gut microbiota at genus level namely Rikenellaceae, Bacteroides, Prevotellaceae_UCG-004, Bacteroidales_RF16 , and Alloprevotella, DgA-11 . It was interesting that blood metabolites, testicular metabolites, and fecal microbiota were well-correlated with sperm parameters. Meanwhile, the blood metabolites and testicular metabolites were well-correlated with microbes. The result indicated that the HF model was beneficial for yak semen quality by improving the gut microbiota and blood metabolism to increase yak fertility.
... The findings of this study provide a basis for Introduction Yak is the traditional livestock in the highlands of China. It provides local herders with the most basic means of living and livelihood materials such as meat, milk, shelter, and fuel (dung) (1,2). However, yaks exhibit low reproductive efficiency, which is attributable to their seasonal reproductive characteristics (breeding period: July-November; when lush pastures provide sufficient nutrition for yaks) has severely constrained the development of yak farming (3). ...
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Full-text available
Yak is the main livestock in the highlands of China. The low reproductive rate of yaks is a serious constraint on their production and utility. N-carbamylglutamate (NCG) can increase arginine synthesis in mammals and has been shown to improve reproductive performance. Twelve multiparous and simutaneous anoestrous female yaks were randomly divided into two groups, one of which was fed the basal diet (Control, n = 6), and the other was fed the basal diet supplemented with NCG at 6 g/day/yak (NCG, n = 6). All yaks were slaughtered on the 32nd day (the time predicted for the selection of the last wave of dominant follicles), and their ovarian tissues were collected and follicles were classified. NCG supplementation increased the number of large ovarian follicles (diameter > 10 mm), as well as caused significant changes in the transcriptional and metabolic levels in yak ovaries which due to the differential expression of 889 genes and 94 metabolites. Integrated analysis of the transcriptomics and metabolomics data revealed that the differentially expressed genes and differential metabolites were primarily involved in the process of energy metabolism, amino acid metabolic pathways, carbohydrate metabolic pathways, and lipid metabolic pathways. The highlighted changes were associated with amino acid synthesis and metabolism, ovarian steroid hormone synthesis, the pentose phosphate pathway, and the tricarboxylic acid cycle, suggesting that NCG supplementation may promote estrogen synthesis and help regulate follicular development by altering the pathways associated with glucose catabolism. The results present important clues for understanding the mechanisms by which NCG supplementation promotes follicular development in yaks. The findings of this study provide a basis for the development and application of NCG in optimizing animal reproduction, including yak reproductive performance, which may help optimize livestock management and uplift the pastoral economy.
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Yak milk is highly nutritious in terms of abundant protein and fat, whereas little is known regarding the influence and mechanism of heat treatments on its gastric emptying and hydrolysis kinetics during digestion in the human gastrointestinal tract. In this study, a bionic human stomach-intestine system was employed to examine in vitro dynamic gastrointestinal digestion of fresh raw and heated yak milks. During gastric digestion, the formation of protein clots or aggregates was observed for all the milk samples. However, significantly more clots were found from autoclaved milk and raw milk, with a dry weight of 14.1 and 10.9 g from 200 g initial milk sample after 30 min digestion, respectively, compared to pasteurized (6.9 g) and microwaved (9.2 g) milks. For both raw and heated milks, the large-sized coalesced fat globules formed in the stomach were rapidly dissociated to small and uneven droplets upon digestion in the small intestinal conditions due to the highly efficient hydrolysis of milk fat globule membrane (MFGM) proteins and fat globules by pancreatic trypsin and lipase. Due to the formation of more dense-structured clots, a longer gastric emptying half-time was shown for the autoclaved (41.1 min) and raw (38.4 min) milks in comparison to that for the yak milks treated with microwave (34.2 min) and pasteurization (36.2 min). Consistently, the pasteurized milk (92.5 %) exhibited the highest protein digestibility at the end of digestion, followed by microwaved milk (87.8 %) ≈ autoclaved milk (86.1 %) > raw milk (80.8 %). The amount of free fatty acids (FFAs) released during digestion in general followed a similar order with that for proteolysis among the milk samples. This study highlights the crucial role of the formation of structured clots in the gastric emptying and hydrolysis of proteins and fat globules. This information will provide a mechanistic understanding of digestion kinetics of yak milk as impacted by heat treatments.
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Grazing (G) yaks (Bos grunniens) are generally of low fertility, which severely limits the income of local pastoralists. However, we recently found that yaks had a 52% higher estrus rate in house feeding (HF) than in G. Gas chromatography-mass spectrometry (GC-MS) and 16S rRNA gene sequencing were used to analyze serum metabolites and fecal microbiota of 20 rutting yaks in the G and HF systems, respectively, to explain this phenomenon. The results showed that 73 total metabolites differed significantly (p < 0.05 and VIP > 1) between the G and HF systems. In the HF system, 53 were upregulated and 20 were downregulated compared with the G system. Organic oxygen compounds, organic acids and their derivatives, and lipids and lipid-like molecules were the most common differential metabolites. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway mapper revealed that 25 metabolic signaling pathways differed significantly between the two systems. The top three enriched pathways included central carbon metabolism in cancer, aminoacyl–tRNA biosynthesis, and ABC transporters. The 16S rRNA gene sequencing data showed no significant differences in Chao 1 index between the two systems. According to principal component analysis (PCA), the HF and G systems were distinctly and separately clustered in terms of fecal microbiota distribution. The G system showed significantly higher abundances of Firmicutes. The HF system showed significantly higher abundances of Alistipes, Treponema, and Rikenellaceae_ RC9_ gut_ group. Pearson's correlation analysis and core network analysis revealed that Rikenellaceae_RC9_ gut_ group, Alistipes, and Treponema were positively correlated with myo-inositol and formed the core bacteria. In summary, the HF system promoted the estrus rate and changed the composition of yak fecal microbiota and serum metabolites. Increased estrus rate might be obtained due to enhanced myo-inositol content in yak serum via the HF system. Correlation analysis suggested that myo-inositol content might also be partly increased via yak-specific fecal microbiota, contributing to the estrus rate. These findings could lead to a novel therapeutic strategy for G yaks due to their low estrus rate.
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Background: Although dietary patterns of highlander have been widely investigated, no study has explored the relationship between dietary patterns and physical examination indicators in high-altitude migrants. This cross-sectional study aimed to investigate the relationship between dietary and physiological indexes and explore the suitable dietary patterns of Tibetan migrants. Methods: 116 participants who had migrated to Tibet for > 2 years were recruited. Dietary patterns and physical examination indicators were assessed using a self-adjusted food frequency questionnaire and blood gas analysis, and six principal dietary patterns were obtained using principal component analysis. Results: The following results were obtained: adherence to a coarse grain dietary pattern was positively associated with mean corpuscular hemoglobin concentration (odds ratio (OR) = 1.077, p = 0.054) and negatively associated with urea level (OR = 0.601, p = 0.013). High meat dietary pattern is positively associated with creatinine level (OR = 1.050, p = 0.023) but negatively associated with glomerular filtration rate (OR = 0.960, p = 0.020). Adherence to the beverage dietary pattern was positively associated with uric acid levels (OR = 1.005, p = 0.044). High fruit intake is positively correlated with aspartate transaminase/alanine transaminase level (OR = 5.271, p = 0.005) and red blood cell count (OR = 4.805, p = 0.033). An unhealthy dietary pattern was positively correlated with lymphocyte counts (OR = 2.904, p = 0.011). Conclusions: In summary, a coarse grain-rich diet is suitable for Tibetan migrants. However, meat and fruit should not be consumed in excessive amounts, and sweetened drinks and alcohol should be avoided.
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Pamir yak milk is considered to be ideal food for local people, but its nutritional profile has not yet been reported. This study investigated the chemical and nutritional composition of Pamir yak milk, and compared the results with reference composition of goat and cow milk. We found that the Pamir yak milk had higher contents of protein (4.30%), fat (4.63), lactose (5.21%) and total solid (14.84%) than that of goat and cow milk. The predominant amino acids were glutamate (20%), proline (10%), lysine (10%) and leucine (10%), of which the essential amino acids accounted for 48% of the total amino acids. Meanwhile, Pamir yak milk was rich in minerals such as Ca, Fe, Zn and Mg and thiamine (B1), niacin (B3), Pyridoxine (B6) and cobalamin (B12) were higher than those of cow and goat milk. Also, medium‐chain fatty acids (C12−C16) exhibited the highest level. However, The α ‐linolenic acid (C18:3), eicosapentaenoic acid and docosahexaenoic acid were found in yak milk. All of the above‐mentioned differences were demonstrated by the fact that the yak milk quality may be affecting by pasture production, animal species and nutritive value of the herbage. Therefore, Pamir yak milk is a promising alternative food that may contribute to human health.
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Alpine breeding systems are an example of sustainable integration between land management and productive processes; forage exploitation has characterized and modified landscape and environment (Brunschwing et al.,1998; Coulon et al., 1997). On the Alps, intensive lowlandstypical breeding methods are generally inapplicable; moreover, the presence of autochthonous breeds characterized by high resistance and adaptation to local environment and fodders has determined the production of typical dairy products, often different from valley to valley. In spite of deep changes that have characterised the social and economic structure of Alpine regions – particularly the breeding activities – mountain farming is still important for keeping a steady equilibrium of breeding systems because it allows the presence of animals during the summer season on alpine pastures....
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Within two groups of lactating Karakachan sheep, grazing mountain pastures in the Bulgarian Rhodope region, respectively one ewe produced milk containing extraordinarily high amounts of c9f11-C18:2 and f10-C18:1. The deviations from the group averages ranged up to about 20 standard deviations for the fl 0-C18:1 isomer in both cases. For one of the two sheep also f11-C18:1 proportion in total fatty acids was increased. Proportions of C18:0 and c9-C18:1 were very low. As the deviating sheep did not receive any treatment differing from that of the other seven and nine animals of the respective groups, it is hypothesized that these changes are due to an inhibition of the terminal step of biohydrogenation in the rumen, possibly by ingestion of an unknown, effective plant species.
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The results of 51 overnight measurements of basal metabolic rate (BMR) in a sample of pastoral nomads resident permanently in Phala, Tibet Autonomous Region, China, are reported. Past studies demonstrated a culturally driven seasonality of diet, with very low summer and very high winter caloric intake. The study was designed to test the hypothesis that the ability of Phala nomads to subsist on low caloric intake for several summer months without signs of malnutrition is explained by lower summer BMR. However, BMR measurements of 40 nomads 13-69 years of age during the summer and remeasurement of 11 nomads during the winter of 1993 provide no evidence for low summer BMR to compensate for the low summer caloric intake. BMR in both seasons is within the normal range predicted by international equations. The BMR of males does not differ from that of females, and the BMR of females averages 7% higher than predicted. Anthropometric evidence reveals that the Phala nomads accumulate body fat during the winter. It is inferred that this may buffer the summer period of low intake. The pattern of subcutaneous fat accumulation in winter, moreover, may afford slight improvement in physiological cold insulation during the severe winters as a consequence of depositing winter fat on the trunk rather than on the periphery. Thus, the dietary seasonality in Phala is a stress that elicits fluctuation in fat energy stores but not BMR. © 1996 Wiley-Liss, Inc.
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Background: Epidemiological studies suggested that consumption of fruit and vegetables may protect against stroke. The hypothesis that dietary antioxidant vitamins and flavonoids account for this observation is investigated in a prospective study. Methods: A cohort of 552 men aged 50 to 69 years was examined in 1970 and followed up for 15 years. Mean nutrient and food intake was calculated from crosscheck dietary histories taken in 1960, 1965, and 1970. The association between antioxidants, selected foods, and stroke incidence was assessed by Cox proportional hazards regression analysis. Adjustment was made for confounding by age, systolic blood pressure, serum cholesterol, cigarette smoking, energy intake, and consumption of fish and alcohol. Results: Forty-two cases of first fatal or nonfatal stroke were documented Dietary flavonoids (mainly quercetin) were inversely associated with stroke incidence after adjustment for potential confounders, including antioxidant vitamins. The relative risk (RR) of the highest vs the lowest quartile of flavonoid intake (greater than or equal to 28.6 mg/d vs <18.3 mg/d) was 0.27 (95% confidence interval [CI], 0.11 to 0.70). A lower stroke risk was also observed for the highest quartile of beta-carotene intake (RR, 0.54; 95% CI, 0.22 to 1.33). The intake of vitamin C and vitamin E was not associated with stroke risk. Black tea contributed about 70% to flavonoid intake. The RR for a daily consumption of 4.7 cups or more of tea vs less than 2.6 cups of tea was 0.31 (95% CI, 0.12 to 0.84). Conclusions: The habitual intake of flavonoids and their major source (tea) may protect against stroke.
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This paper reviews the state of our knowledge regarding the effects of the Pleistocene/Holocene transition on the kinds and range of human adaptations in what is now Peru. Following a discussion of geological, paleoclimatic, and archaeological data, the paper focuses upon four aspects of environmental change with specific regard to how these would have affected human adaptations: environmental changes on the Pacific littoral, the extinction of Pleistocene faunal and floral species and their replacement with modern faunas, the adaptive radiation of these modern flora and fauna, especially into the Andean highlands, and characteristics of newly available high elevation environments that would have affected the process by which foraging peoples moved into them. Although Pleistocene fauna have been discovered in Peru, none of these finds have been made in the context of indisputable human activity, and therefore, the effect of their extinction on early foraging peoples is unknown. The earliest acceptable archaeological sites in Peru date around 11–12,000 years ago, and are found on the coastal lowlands. The highlands were not occupied until after 11,000 years ago. While high elevation environments were attractive after 11,000 years ago, they were only slowly occupied by humans due to the constraints of the combined effects of hypoxia and cold.