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).
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).
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).
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).
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).
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).