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Blue Japanese oak (Quercus glauca)


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Common names 

Blue japanese oak, ring-cupped oak, bamboo-leaved oak, glaucous-leaf oak [English]; chêne bleu du Japon [French]; bambusblättrige eiche [German]; quercia a foglie di bamboo [Italian]; السنديان الأغبر [Arabic]; 青剛櫟 [Chinese]; アラカシ [Japanese]; सानो फलाँट [Nepali]


Cyclobalanopsis glauca (Thunb.) Oerst., Quercus myrsinifolia Blume


Blue Japanese oak (Quercus glauca Thunb.) is medium-sized tree native of Asia used as fodder in Nepal and India.


Blue japanese oak is an evergreen tree, 10 to 20 m high in its native Asia and slightly smaller (8-10 m) under Mediterranean conditions. It has a straight cylindrical bole, up to 45 cm in diameter, covered with greyish bark (Hélardot, 2015; Ducatillion, 2010; Orwa et al., 2009). The tree may be multi-stemmed (NC State University, 2015). The crown is oval to rounded. Its branches are widely spread, and young twigs are glabrescent, thick, stiff, dark olive green with pale lenticels. Blue japanese oak is taprooted (Hélardot, 2015; Ducatillion, 2010; Orwa et al., 2009). The leaf blades are evergreen, alternate, simple, oblong to obovate-oblong, acuminate at the apex and broadly cuneate at the base, serrated, 7-13 cm long and 4-5 cm broad. The upper face of the leaf is glabrous and glossy green and the lower face is silky hairy, blue green in colour (Hélardot, 2015; Ducatillion, 2010; Orwa et al., 2009; Forestry Nepal, 2005). New foliage is a rich green or bronze to purplegreen (Forestry Nepal, 2005). Flowers are dioecious catkins. Male flowers are silky hairy, loose drooping catkins: they bear 4 stamens. Female catkins are shorter and bear 2-4 flowers. The fruits are 1.5-2 cm long x 0.9-1.4 cm broad, ovoid acorns, generally borne in clusters (3 fruits/cluster). A third or half of the fruit is enclosed in a ringed, scally silky cup (Hélardot, 2015; Forestry Nepal, 2005).


Blue japanese oak acorns are edible, but their high tannin content makes it necessary to leach them prior to grinding. This can be done by thorough washing of the acorns or by burying the acorns in the ground overwinter. Leaching the flour may be more efficient however (Orwa et al., 2009). The acorns can be dried, ground into powder and used as flour in mixture with cereals to make breads. The powder can also be used as a thickening agent in stews. Roasted seeds can be used as coffee substitute (Orwa et al., 2009). Leaves can be cooked and eaten as vegetable in times of scarcity (Orwa et al., 2009).The branches and twigs are good material for culturing mushrooms (for example, Pleurotus eryngii) (Ducatillion, 2010). Blue Japanese oak is subject to galls that are source of tannin and dye. The wood is a good quality timber, finely textured, hard and durable. and is also valuable fuelwood (Orwa et al., 2009). The tree is planted as an ornamental in gardens, parks and streets since it is nicely shaped and provides desirable shade (Orwa et al., 2009). The leaves and stems are valuable fodder, relished by deers in the USA. The leaves are used to feed oak tasar silkworms in the hilly regions of China and India (Arindam Basu, 2015; Ducatillion, 2010).


Blue japanese oak is found in evergreen broad-leaved forests in north subtropical and warmer temperate zones of Asia. In Nepal, it is typically found in Chilaune (Schima wallichii) - Katush (Castanopsis indica) degraded forests and in association with banj oak (Quercus leucotrichophora) and woolly-leaved oak (Quercus lanata) (Orwa et al., 2009; Forestry Nepal, 2005). Blue japanese oak is native of China, Japan, Nepal, Pakistan and Vietnam and is now found in Europe, the USA and the Mediterranean Basin (Ducatillion, 2010; Orwa et al., 2009). In Nepal, it often develops well on moist, northern faces and sides of ravines (Forestry Nepal, 2005). Blue japanese oak is found from 300 m to 3100 m altitude in places where annual rainfall ranges from 1000 to 2900 mm and where average annual temperature is between 6°C and 19°C. It can grow on many types of soil but does better on light to medium, acid to neutral, well-drained, moist soils. It can withstands dry spells provided it could establish under moist conditions. It is moderately hardy and some trees were killed by -12° C to -16°C in French Mediterranean areas (Ducatillion, 2010). Blue japanese oak does well on slightly acidic or slightly saline loams and neutral limestone soils. Pure stands often occur on moist clays underlain with sandstone and shale (Orwa et al., 2009). The tree prefers moist situations, such as north aspects and the sides of the ravines, and grows well on deep clay loams (Forestry Nepal, 2005). It should not be planted on dry sites (Forestry Nepal, 2005).

Forage management 

Blue japanese oak can be directly sown or in nursery beds. Since it quickly develops a deep taproot, it is advisable to sow it in its definitive place. If the seedlings are sown in nursery beds they should not be left more than 2 growing seasons so that the taproot does not develop too much. Bare-root planting gives very poor results (PFAF, 2014; Orwa et al., 2009). The seedlings are sensitive to frost and must be protected during winter, but older trees are more frost-resistant (Orwa et al., 2009). Blue japanese oak is a slow-growing species: 2-year seedlings reach 50 cm (Forestry Nepal, 2005). The tree coppices freely (Orwa et al., 2009). Well-managed plantations reach 8 m in height and 7.5 cm diameter after 14 years (Orwa et al., 2009). In Nepal, blue japanese oak is used as a fodder but its use varies greatly from one place to another. Average annual fodder yield is 80-100 kg of fresh matter per tree (Forestry Nepal, 2005).

Nutritional aspects
Nutritional attributes 

The nutritional value of the leaves is rather poor, with a low protein content (about 10% DM) and large amounts of fibre and tannins.

Potential constraints 

Oak poisoning

Like other oak species, blue japanese oak may have detrimental effects on animal health. In oak poisoning, clinical signs occur 3-7 days after consumption of large quantities of young oak leaves in the spring or green acorns in the fall. Outbreaks have occured when hungry animals accessed to fallen trees associated with a recent storm. Mortality as high as 70% has been seen. In dams, the consumption of acorns during second trimester of pregnancy resulted in malformed calves and abortions. The toxicity could be due to pyrogallol, gallotannins, polyhydroxyphenolic compounds, or their metabolites produced by microbial hydrolysis in the rumen, which bind and precipitate proteins, and result in general and renal dysfunction (Blakley, 2013).

Blue japanese oak seeds contain high levels of tannins that may be toxic to animals and humans. It is recommended to wash them thoroughly before using them (Orwa et al., 2009). When fed at high levels, oak leaves produce toxic effects (Lohan et al., 1983; Makkar et al., 1991). Their tannin content increases with maturity but the protein precipitation capacity of theses tannins is among the lowest in the genus Quercus (Makkar et al., 1991).  Incorporation of Quercus incana leaves into mixed rations above 14% (on dry weight basis) has been shown to have adverse effects (Lohan et al., 1983). Feeding at higher levels or as sole feed results in oak poisoning (Makkar et al., 1991). Although growing conditions are known to influence tannin levels, it was inferred that the mature leaves of blue japanese oak (Quercus glauca) would produce adverse effects even at lower levels of feeding, as the tannin levels in leaves of this species are higher than those of Quercus incana (Lohan et al., 1983). Feeding mature leaves of blue japanese oak might be more deleterious than feeding younger leaves (Makkar et al., 1991). Mixed beef cattle experimentally fed on blue japanese oak leaves showed clear clinical and histological signs of poisoning, resulting in the death of 2 animals out of 4 (Hwang et al., 1991a; Hwang et al., 1991b).


Though blue japanese oak leaves are of limited nutritional value and toxic to livestock (See Potential constraints), they are harvested in Nepal for direct feeding or for storage and subsequent use as fodder in times of scarcity (Lohan et al., 1983; Bajracharya et al., 1985 cited by Paterson, 1993). In Manipur (Northeastern India), cattle and goats consume the acorns and the leaves are lopped by farmers to feed cattle at the end of the lean season, from January to May (Koireng et al., 2015). In a survey of smallholder farmers in the Garhwal Himalaya (Northern Himalaya), Quercus glauca was mentioned as a fodder species in oak-dominated zones, but with much lower marks than Quercus floribunda for nutritive value and milk production capacity (Dhani Arya et al., 2011).


Blue japanese oak acorns have been described as potentially useful as poultry feed due to their nutrient content (Marwat et al., 1978). However, their high tannin content would require thorough processing before they can be used as feed.


Unlike other oak species, no information seems available in the international literature on the utilization of Quercus glauca leaves or acorns in rabbit feeding (January 2016).

Nutritional tables
Tables of chemical composition and nutritional value 

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used

Main analysis Unit Avg SD Min Max Nb  
Crude protein % DM 10.7 1.0 9.6 11.6 3  
Crude fibre % DM 29.0       1  
NDF % DM 69.4       1  
ADF % DM 70.5       1  
Ether extract % DM 5.7   4.1 7.2 2  
Ash % DM 8.5   7.6 9.4 2  
Gross energy MJ/kg DM 18.8         *
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 18.7       1  
Phosphorus g/kg DM 2.3       1  
Manganese mg/kg DM 146       1  
Zinc mg/kg DM 37       1  
Copper mg/kg DM 6       1  
Iron mg/kg DM 174       1  
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants % 42.5       1  
Energy digestibility, ruminants % 40.0         *
DE ruminants MJ/kg DM 7.5         *
ME ruminants MJ/kg DM 6.1         *
Nitrogen digestibility, ruminants % 48.0       1  

The asterisk * indicates that the average value was obtained by an equation.


IVRI, 2011; Makkar et al., 1998; Sen, 1938

Last updated on 16/09/2016 10:55:05

Datasheet citation 

Heuzé V., Tran G., Lebas F., 2016. Blue Japanese oak (Quercus glauca). Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. http://www.feedipedia.org/node/109 Last updated on September 16, 2016, 11:32

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