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Spear grass (Heteropogon contortus)

Datasheet

Description
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Common names 

Spear grass, speargrass, black speargrass, tanglehead grass, tanglehead, bunch speargrass, bunched spear grass, twisted beardgrass, tangle grass, piercing grass, pili grass, stick grass, wild oats [English]; flechinha [Portuguese]; hierba torcida [Spanish]; herbe polisson, hétéropogon contourné, herbe barbue, herbe à moutons [French]; assegaaigras, steekgras [Afrikaans]; pili [Hawaii]; kichoma mguu, kichoma nguo, kishona nguo, kishona [Swahili]; 黄茅, 地筋 [Chinese]; หญ้าหนวดฤๅษี [Thai]

Synonyms 

Andropogon contortus L., Heteropogon hirtus Pers., Heteropogon hispidissimus A. Rich.

Related feed(s) 
Description 

Spear grass (Heteropogon contortus (L.) Beauv. ex Roem. & Schult.) is a tropical perennial grass. It grows to a height of 50 to 150 cm, is tufted and highly variable. Its stems are geniculated at the base, erect at their upper levels, often branched, particularly at flowering (Cook et al., 2005). The leaves are green or bluish green, usually glabrous or with few long hairs at the base. The leaf-blade is folded when young, then flat at maturity, 3-30 cm long, 2-8 mm broad, and somewhat canoe-shaped at the apex (Soromessa, 2011; Cook et al., 2005). The inflorescence is a 3 to 8 cm long raceme borne single or in pairs at the axil of the upper leaves. The spikelets are paired and very dissimilar according to their position on the raceme. Male or sterile spikelets are awnless, sessile and borne at the base of the raceme, or pedicellate and borne at the apex. Bisexual spikelets are only borne at the apex and they are all awned. The long awns (5-10 cm long) and the way they become twisted as the seeds mature are a characteristic trait of spear grass. The seed is a caryopsis, 3.5-4.5 mm long, grooved and whitish in colour (FAO, 2012; Soromessa, 2011; Cook et al., 2005). There were considerable numbers of local species and varieties in the early botanical literature. Only a few commercial varieties are available, for example "Rocker" from Arizona and "Kahoolawe" from Hawaii (Soromessa, 2011).

Spear grass is mainly used as fodder when it is young. It can be grazed or cut for hay or silage. Once flowering occurs, its overall nutritive value declines and the sharp-pointed seeds and tangled awns may injure animals and humans (see Potential constraints on the "Nutritional aspects" tab). It should then not be grazed or cut for fodder after flowering (Soromessa, 2011). Spear grass is used for thatching, matting or making cellulose for paper, and provides environmental services as a cover crop and biodiversity nest (see Environmental impact below) (Soromessa, 2011; Cook et al., 2005).

Distribution 

Spear grass is native to the tropics and subtropics of Africa, Southern Asia, Northern Australia and Oceania and is naturalized in tropical and subtropical areas of America, East Asia and the Pacific Region. Spear grass is a summer-growing grass, highly resistant to grass fires. It is a species of savannahs and open forests (Combretum-Terminalia) (Cook et al., 2005). Heteropogon contortus is seldom cultivated and usually found wherever grasslands are periodically burned. Spear grass mainly grows from 30°N to 30°S and from sea level up to an altitude of 3800 m (Cook et al., 2005; Göhl, 1982). It is found from sub-humid to semi-arid areas in the tropics and subtropics where annual rainfall is comprised between 600 and 1000 mm, but it can grow under rainfall lower than 210 mm (Soromessa, 2011). It is tolerant of frost but does not grow during winter (FAO, 2012). Spear grass does not withstand waterlogging but may bear short periods of flooding. Heteropogon contortus can grow on a wide range of well-drained soils provided they are neither too infertile nor too saline. Optimal pH for spear grass ranges from 5 to 6. It has some tolerance of light shade (Cook et al., 2005).

Forage management 

Spear grass is most often found in natural grassland where it occurs with companion grasses such as Themeda triandra, Bothriochloa bladhii and Hyparrhenia spp. When it is cultivated, it can be propagated from seeds, or more easily through vegetative propagation. Once established, and if defioliation is not too heavy, spear grass may survive several years. It has been profitably mixed with low fertility legumes such as Stylosanthes guianensis, Stylosanthes hamata, Stylosanthes humilis and Stylosanthes scabra, or with Macroptilium atropurpureum, Lototonis bainesii, Aeschynomene falcata, Chamaecrista pilosa and Chamaecrista rotundifolia. Mixing spear grass with these legumes increased the DM yield and stocking rate of the stand (Cook et al., 2005).

Annual DM yields are very variable and depend on soil fertility and rainfall. They range from about 0.5 to 8.7 t/ha. Spear grass does not withstand heavy grazing and may become dominated by other grasses such as Digitaria didactyla and Aristida spp. (Cook et al., 2005). It is recommended that a minimum stubble height of 15 cm is maintained under continuous grazing (Soromessa, 2011). In order to improve survival it is recommended to defer grazing for 4 to 6 months or to reduce stocking rates after burning the stands in spring. Fire is not recommended when spear grass is growing with stoloniferous species such as Digitaria didactyla or Cynodon dactylon (Cook et al., 2005). Under rotational grazing, a forage height of 10-25 cm should be maintained (Soromessa, 2011).

Environmental impact 

Carbon resevoir and desertification controller

In drylands of Zimbabwe, spear grass (Heteropogon contortus) has been used to re-green desertified areas and to increase carbon sequestration, as shown in the following video (Itzkhan, 2014):

Weed

Heteropogon contortus is declared a weed in some regions of America, East Asia and in New-Caledonia (USDA, 2012; Cook et al., 2005; Gargominy et al., 1996). However, in Hawaii, there are attempts to restore native populations of spear grass, as it has been outcompeted by foreign grassland species such as buffel grass (Cenchrus ciliaris) (Cook et al., 2005). 

Host for diseases

Heteropogon contortus acts as a collateral host for downy mildew on sorghum and maize (Soromessa, 2011).

Erosion control

In the USA, an improved cultivar of spear grass (Rocker) was recommended for the stabilization of critical areas, rangeland revegetation and erosion control along roadways, construction sites and other disturbed areas in the South-West desert (Pater, 1995). In India, spear grass could prevent erosion on up to 20° slopes (FAO, 2012).

Nutritional aspects
Nutritional attributes 

Heteropogon contortus has a low nutritional value: it has a high cell wall content (about 75% NDF in the DM), it is low in protein (3-9% DM) and deficient in minerals (P, Ca, Mg, S, Cu, Zn) (Freire et al., 1980; Morrison et al., 1990; Tefera et al., 2009). Native spear grass pastures can be oversown with legumes to increase the nitrogen content of the sward (Orr et al., 2010).

Potential constraints 

Eye, mouth and skin injury

The seeds of mature plants can induce corneal opacity syndrome in grazing animals (Prasad et al., 1980). Sheep and goats appear more sensitive than cattle and buffaloes to mouth ulceration from hard seeds contained in milled forages, even though grazing animals are able to avoid them by selection (McSweeney et al., 1988). Bristles from spear grass seeds were observed at the upper lateral neck region of lambs, near the larynx. The sharp base of the bristle penetrates the skin against body movement, and the susceptibility in lambs can be explained by the lack of a thick wool coat (Narayanan et al., 2003). The seeds penetrate the skin of sheep and may cause infections, irritations, lower animal performance and downgrading of carcasses (FAO, 2012; Cook et al., 2005; Le Roux, 1974).

Wool quality

The barbed seeds of spear grass may raise concern in sheep as they twist in the wool and hamper its quality (Cook et al., 2005).

Ruminants 

Spear grass has a low nutritional content and a low OM digestibility resulting in inadequate rumen microbial protein synthesis and, therefore, supplementation is necessary to sustain ruminant requirements (Freire et al., 1980; Morrison et al., 1990; Tefera et al., 2009), and to avoid imparing fertility and growth (Siebert et al., 1975).

Palatability

Spear grass has a moderate palatability compared to many other tropical grasses (Hendricksen et al., 2010; O'Reagain et al., 1996; Tetteh, 1974). It is moderately or little grazed (Tetteh, 1974). Its palatability depends on the season and growing conditions. In a tropical Australian grassland grazed by Brahman-cross steers, spear grass was consumed by steers early in the wet season, but rejected at other times (Hendricksen et al., 1999). Cattle selectively grazed spear grass that had been burnt in spring rather than spear grass that had not been burnt (Orr et al., 1997).

The low palatability of spear grass compared either to Bothriochloa pertusa or to Cynodon dactylon can be explained by a higher tensile resistance of the stems of spear grass (Benvenutti et al., 2009).

Pasture

Cattle

Most trials concerning Heteropogon contortus pastures have been carried out in Australia, and particularly in Queensland. Annual live-weight gains per head in a native pasture of spear grass were highly variable between years, ranging from a low of 43 kg/steer at 2 ha/steer to a high of 182 kg/steer at 8 ha/steer. They were consistently higher at light stocking and decreased with increasing stocking rate. Cattle productivity was sustainable when stocking rates were maintained at 4 ha/steer or lighter, because at higher levels (up to 2 ha/steer) there was a negative impact of stocking rates on pasture productivity, which resulted in undesirable changes in species composition (Burrows et al., 2010; Orr et al., 2010).

On dry season native pastures (predominantly spear grass), with a mixture of molasses, urea, minerals and cottonseed meal, Brahman steers grew faster than unsupplemented steers (Lindsay et al., 1998). Several trials showed the advantage of improving native spear grass pasture by oversowing with legumes such as alfalfa, Macroptilium atropurpureum, Stylosanthes guianensis, Stylosanthes humilis, Chamaecrista rotundifolia or with buffel grass (Cenchrus ciliaris) even if there were risks in establishment (Clark, 1980; MacLeod et al., 2004; Partridge et al., 1992). Supplementation of the diet with cottonseed meal or copra meal can also be valuable (Gulbransen et al., 1990). All these practices resulted in significant increases in live-weight gain. The live-weight gains of steers during the wet season were only slightly greater on burnt than on unburnt pasture. Due to the uncertainty of precipitation and subsequent regrowth, it was considered more practical to graze unburnt pastures and supplement the diet (McLennan et al., 1986).

There are few studies on spear grass fed to dairy cows. In India, Murrah buffaloes produced more milk when they were fed a complete feed block diet consisting of a 60:40 mixture of roughage (dried chaff of Sehima nervosum and spear grass) and a concentrate, than with wheat straw and 4 kg concentrate (Samanta et al., 2007).

Small ruminants

In India (Tamil Nadu), lambs grazing native pastures (mainly of spear grass) supplemented with 100 g/d of concentrate gained 34 to 107 g/d (Prasad et al., 1973). In the Himalayas, DM intake/head/month was relatively higher for goats than for cattle in a pasture dominated by Arundinella nepalensis and Heteropogon contortus (Agrawal et al., 1989).

Hay

Cattle

Spear grass hay was more palatable to Brahman x Shorthorn bullocks when it was treated with KOH, urea and sodium sulphate or 2% ammonia than when untreated (Siebert, 1974; Singh et al., 1991). The treatment increased the digestibility of organic matter and cell wall contents, and organic matter intake, so that the calculated intake of metabolizable energy increased by 51%. Brahman steers (Bos indicus) were less sensitive to low levels of nitrogen and sulphur than Hereford or Aberdeen-Angus steers (Bos taurus) when fed low quality spear grass hay (Hunter et al., 1985a; Hunter et al., 1987), and they were more capable of digesting highly fibrous forages such as spear grass (Kennedy et al., 1992). However, supplementation with rumen-degradable nitrogen and sulphur only significantly increased DM intake in Hereford steers (Hunter et al., 1985b). This effect can be explained by an improved microbial growth in the rumen when nitrogen and sulfur deficiencies are corrected, resulting in a faster rate of digestion and an increased feed intake (Hunter et al., 1980).

Spear grass hay supplemented with 1 kg/d of concentrate (fortified molasses or lupins) was found to sustain the nutritional requirements of steers (Krebs et al., 2004).

Small ruminants

Due to its low nitrogen content, chaffed spear grass hay is better utilized by goats than by sheep (Malsur et al., 1998). Pelleting was found to be a better processing method than chopping or grinding for nutrient utilization in male goats and rams fed spear grass hay supplemented with 250 g concentrate/head/d (Reddy et al., 1994). Leucaena leucocephala is a good candidate to supplement spear grass: it increased DM intake in goats and non ammonia nitrogen flows from the abomasum (Bamualim, 1985). Providing a small amount of concentrate (100-200 g) sustained the nutritive requirements of wethers (Krebs et al., 2004).

Pigs 

In India, 4-4.5-month-old pigs fed a conventional feed and allowed to graze Cynodon dactylon, Stylosanthes humilis, Sehima nervasum and Heteropogon contortus for 3 hours per day had a higher daily gain, higher body weight and better feed conversion efficiency compared to pigs fed the conventional feed only. Higher body weight was observed when the grass was pen-fed rather than grazed (Singh et al., 1998).

Rabbits 

No information found (2012).

Nutritional tables

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  
Dry matter % as fed 39.1 10.7 17.1 57.5 13  
Crude protein % DM 5.0 1.7 2.8 9.3 61  
Crude fibre % DM 37.0 2.4 31.2 40.0 24 *
NDF % DM 74.5 1.2 71.1 76.1 35  
ADF % DM 42.0 2.4 38.2 47.8 36  
Lignin % DM 5.2 1.0 3.7 7.5 25  
Ether extract % DM 1.4 0.2 1.1 1.8 18  
Ash % DM 8.8 1.5 6.6 12.9 61  
Gross energy MJ/kg DM 17.9         *
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 2.1 0.8 1.1 3.9 23  
Phosphorus g/kg DM 1.0 0.4 0.3 1.6 49  
Potassium g/kg DM 7.3 1.9 4.3 11.3 22  
Sodium g/kg DM 0.2 0.1 0.0 0.4 18  
Magnesium g/kg DM 1.5 0.3 0.9 2.2 49  
Manganese mg/kg DM 74 48 4 176 19  
Zinc mg/kg DM 47 26 15 104 40  
Copper mg/kg DM 12 9 3 40 43  
Iron mg/kg DM 600       1  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, Ruminant % 58.9 6.3 33.7 58.9 9 *
Energy digestibility, ruminants % 56.3         *
DE ruminants MJ/kg DM 10.1         *
ME ruminants MJ/kg DM 8.2         *
Nitrogen digestibility, ruminants % 41.4       1  

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

References

CGIAR, 2009; CIRAD, 1991; Holm, 1971; Kennedy et al., 1992; Sen et al., 1965; Sultan et al., 2008; Tefera et al., 2009; Walker, 1975

Last updated on 15/04/2013 13:50:48

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 92.6       1  
Crude protein % DM 3.2 0.8 2.3 4.2 13  
Crude fibre % DM 38.7 4.6 29.8 40.1 4 *
NDF % DM 79.7 3.3 71.4 81.3 30  
ADF % DM 46.3   44.9 46.3 2 *
Lignin % DM 8.1 2.1 6.0 9.9 4  
Ether extract % DM 1.3 0.3 1.0 1.7 4  
Ash % DM 7.3 0.4 7.0 9.1 32  
Gross energy MJ/kg DM 18.2         *
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 7.0   7.0 7.0 2  
Phosphorus g/kg DM 1.0   1.0 1.0 2  
               
Ruminant nutritive values Unit Avg SD Min Max Nb  
OM digestibility, Ruminant % 53.7 7.5 31.5 55.8 11 *
Energy digestibility, ruminants % 50.4         *
DE ruminants MJ/kg DM 9.1         *
ME ruminants MJ/kg DM 7.5         *
Nitrogen digestibility, ruminants % 32.2 25.5 -14.3 59.0 6  

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

References

Hunter et al., 1980; Hunter et al., 1985; Hunter et al., 1987; Lander et al., 1928; Playne, 1972; Reddy et al., 1994; Romero et al., 1976; Sen, 1938

Last updated on 15/04/2013 14:08:54

References
References 
Datasheet citation 

Heuzé V., Tran G., Giger-Reverdin S., Lebas F., 2017. Spear grass (Heteropogon contortus). Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. http://www.feedipedia.org/node/433 Last updated on January 16, 2017, 15:41

English correction by Tim Smith (Animal Science consultant) and Hélène Thiollet (AFZ)