Andropogon gayanus is relished by all classes of ruminant livestock (cattle, sheep and goats). It is mainly grazed in permanent pastures: it is palatable when young and is used for continuous and rotational grazing (Cook et al., 2020). It is also used for cut-and carry systems or made into hay. As gamba grass is poor in minerals (except K), livestock grazing it exclusively will have to be provided with mineral supplementation to prevent deficiencies.
Palatability
In Africa, gamba grass is recognized as being a productive and highly palatable fodder when green at vegetative stage (Ibrahim, 2012). Young leaves are palatable, readily eaten and accepted by cattle throughout the year under moderate grazing pressure (Bewabi et al., 2018). Nutritive value declines rapidly with age and a decreasing leaf/stem ratio (Phengsavanh et al., 2003). With maturity, gamba grass produces numerous hard and unpalatable flowering stems. Burning or mowing them could improve the palatability of gamba grass pastures for grazing animals (Aina et al., 2020).
In Ghana, grazing intensity was assessed among a variety of pasture grasses including Andropogon gayanus, Paspalum scrobiculatum, Panicum maximum, Setaria sphacelata, Digitaria decumbens and Sporobolus pyramidalis, Vetivaria fulvibarbis, Brachiaria lata, Cenchrus ciliaris, Eleusine indica, Axonopus compressus, and Heteropogon contortus. Gamba grass was reported to be the preferred species (Tetteh, 1974).
In Benin, gamba grass belonged to the top 16 grasses cited or reffered to for their fodder value by livestock farmers during pasture walks. It was among the most common species used as fodder with Megathyrsus maximus, Pterocarpus erinaceus and Fluegga virosa (Ouachinou et al., 2018)
Digestibility and degradability
Pasture
Assessement of gamba grass pasture digestibility have been made with in vitro measurements for dry matter (IVDMD) and organic matter (IVOMD). In vitro DM digestibility rose to 63% during the wet season but dropped to 30-40% at the end of the dry season (Cook et al., 2020). In Venezuela, the only factors influencing IVOMD were the frequency of defoliation and rainfall. IVOMD decreased from 54 to 52% with increasing harvest interval from 63 to 84 days, respectively. Digestibility was a function of rainfall. Thus, the highest IVOMD (57%) were found at 63 days of age with high rainfall. These results confirm that gamba grass has moderate nutritional value in terms of digestibility. More frequent harvesting could help to improve gamba grass forage quality even though this might reduce DM yield. N and P fertilizers had no effect on IVOMD (Caraballo et al., 1997).
African basil (Ocimum gratissimum) could be used to reduce quadratically methane emissions arising from the ruminal fermentation of gamba grass by reducing overall digestibility of the forage (Kouazounde et al., 2015).
Hay
Apparent in vivo digestibility at three different stages (56, 84 and 112 days of growth) were assessed, and the highest digestibilities were obtained at the earliest stage (56 days) with values of 62%, 56%, 59% and 63% recorded for dry matter, crude protein, crude fibre, and energy respectively (Cavalcanti et al., 2016). Similar results were obtained with DM degradability assessed with the production gas method: gamba grass hay harvested between 56 and 84 days had higher degradability values than hay harvested at 112 and 140 days (Moreira et al., 2013).
Silage
A study conducted in Brazil showed that gamba grass produced higher quality silage (higher lactate and lower pH and butyrate content) after 112 days of regrowth. As for hay, IVDMD of gamba grass silage was the best at 56 days of age (57%).
Ensiling can be useful to prevent the reduction of quality during the dry season of tropical savannah. Gamba grass silage, harvested at three stages of maturity (56, 84 and 112 days) from an established pasture was used to evaluate the in situ rumen degradability with cannulated cattle (Ribeiro et al., 2014a). Gamba grass ensiled at 56 days of regrowth had higher nutritional value. Gamba grass ensiled at 84 d of regrowth had highest slowly degradable DM fraction and lowest DM effective degradability. The DM effective degradability decreased with grass maturity because of the increasing stem/leaf ratio and reduction of stem nutritional quality (Ribeiro et al., 2014a)
Cattle
Gamba grass was reported as one of the most common species used as fodder for grazing cattle in Benin. Supplementation of gamba grass with legumes helped to increase the ruminant production from 90-120 to 150 kg live weight gain/head/yr (Ouachinou et al., 2018).
Pasture
In Colombia, a study assessed the performance of cattle grazing on a low fertiliser-input and well managed gamba grass dominated pasture (70–75%) with 73% NDF and 8.7% CP during the rainy season and 74 % and 8.9 % CP over the dry season. DM intake of the grazing cattle was 2.33±0.13 % of total LW. The performance of cattle of different ages grazing gamba grass dominated pasture was close to that obtained on pasture of Stylosanthes capitata. Steers grazing the gamba grass pasture gained up to 24% more weight than did cull cows, but the latter emitted significantly less CH4 than the steers (129 vs 141 g/day). Live weight gain could be improved when cattle grazed gamba grass in combination with legumes (Ramirez-Restrepo et al., 2019).
Hay
In Nigeria, gamba grass hay was offered to White Fulani heifers at three levels of feeding during the wet season and the dry season (regrowth). The hay DM intake varied from 47.7 to 68.3 g/kg LW0.75. The effect of level of feeding on hay intake was largely independent of the selection for CP and shows that the animals preferred leaves against stems (Zemmelink et al., 1972). Male zebu calves (Wadara) (99.2 kg BW) fed on a gamba grass hay basal diet and concentrate had a daily feed intake of 3.1 kg and daily weight gain of 152.9 g. Supplementation of the gamba grass basal diet with a protein source like pods of Acacia sieberiana had a slight positive effect on feed intake and daily weight gain. Adding A. sieberiana to gamba grass hay reduced feeding costs significantly (Ibeawuchi et al., 1998).
Sheep
Pasture
In Brazil, the assessment of daily idleness of sheep on different pastures showed that the highest values were obtained on gamba grass pasture (12.06 h) which suggested that this pasture led to lower acceptability and grazing activity (Sousa et al., 2016). The average daily gain (ADG) of sheep on gamba grass pasture (55g LWG/d) was much lower than on Brachiaria spp. (116 g LW/d) and Megathyrsus maximus (111.6 g LW/d). This suggested that gamba grass is less adequate for sheep than Brachiaria spp. and Megathyrsus maximus pastures (Gracindo et al., 2014).
Hay
In Burkina Faso, five tropical forage hays including Andropogon gayanus were fed to Djallonke sheep to measure DM voluntary intake and OM digestibility. DM intake of gamba grass hay ranged from 68 to 26 g/kg BW 0.75, and OM digestibility ranged from 31% to 56%, with both parameters depending on the phenological stage. DM and OM digestibility for gamba grass hay were lower than those obtained for hays of Panicum anabaptistum, Pennisetum pedicellatum, Brachiaria lata and Andropogon pseudapricus (Kaboré-Zoungrana et al., 1999).
In Northern Nigeria, Gamba grass hay remains available when other feeds are scarce and it could be fed to Yakasa rams (18 kg BW). Gamba grass hay could be profitably supplemented with groundnut haulms, a crop residue also available in times of scarcity. Together, gamba grass hay and groundnut haulms could improve the dry matter intake, nutrient digestibility, nitrogen utilization and enhanced growth rates of rams (Mbahi et al., 2016).
Silage
In Brazil, gamba grass silage made at different ages of regrowth (56, 84 and 112 d) was used to evaluate intake, digestibility and methane emission from sheep. Silage DM intake ranged from 51.8 to 57.0 g/kg metabolic weight and was not influenced by age of regrowth, but apparent DM digestibility linearly decreased from 53% to 38% with increasing age of regrowth. These results suggest that gamba grass should be ensiled at early age of regrowth (56 d) for better digestive efficiency and silage quality. The age of regrowth did not influence methane emissions. The moderate nutritional value of these silages suggests that protein supplementation would be required to improve animal productivity (Ribeiro et al., 2015a).
Goats
Pasture
In Brazil, grazing goats were observed in three cropping systems consisting in a monoculture of Andropogon gayanus and two intercropping systems of gamba grass + legumes. Gamba grass monoculture had the lowest protein content and digestibility, the highest NDF content and the longest grazing time. Daily DM intake in the gamba grass monoculture was 2.7% LW with an average daily weight gain of 85 g/d. DM intake was lower for gamba grass than for the intercropping mixtures, while the average daily gain did not differ between the systems (Moura et al., 2020).
Hay
In Nigeria, gamba grass hay was used to evaluate the effects of four treatments (hay + water, hay + NaOH solution, hay + two native alkali salts from Nigeria) on digestibility with goats. Alkali treatment increased significantly DM intake and improved digestibilities of dry matter, protein, and crude fibre. Daily DM intake on gamba grass was 19.43 g/kg metabolic weight (Ibeawuchi et al., 1991).
