Gamba grass (Andropogon gayanus) is relished by all classes of livestock (cattle, sheep and goats). Gamba grass is mainly grazed in permanent pastures: it is palatable when young and is used for continuous and rotational grazing (Cook et al., 2020). It can also be used for cut-and carry systems or made into hay.
Composition
As a drought resistant forage grass, it is known to have medium nutritional value (Miles, 1980). Gamba grass nutritional value is moderate in young growth. When the plant reaches maturity, it coarsens and nutritional value declines after flowering (Cook et al., 2020). Gamba grass is extremely deficient in Ca, P, Mg, and Na concentrations for grazing ruminants (Morillo et al., 1997). Only average K content was considered adequate. There is thus a need for mineral supplementation to prevent deficiencies in ruminants fed on gamba grass forage as a sole source of feed.
Palatability
In Africa, gamba grass is recognized as being a productive and highly palatable when green at vegetative stage (Ibrahim, 2012). Young leaf of gamba grass is palatable, readily eaten and accepted by cattle throughout the year under moderate grazing pressures (Bewabi et al., 2018). However nutritive value declines rapidly with age and 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 like gamba grass (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 also among the most common species used as fodder with Megathyrsus maximus, Pterocarpus erinaceus and Fluegga virosa (Ouachinou et al., 2018)
Degradability, digestibility
Pasture
IVDMD could be up to 63% during the wet season but drops to 30‒40% at the end of the dry season (Cook et al., 2020).
In Venezuela, an experiment assessed in vitro organic matter digestibility (IVOMD) of gamba grass and reported that the only factors influencing IVOMD were the frequency of defoliation and rainfall (Caraballo et al., 1997). The average IVOMD decreased from 54.2 to 51.7% with increasing harvest interval from 63 to 84 days, respectively. Digestibility was a function of rainfall. Thus, the highest IVOMD (56.5%) 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.
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 digestibility of dry matter (DM), crude protein (CP), fibre fractions (CF), energy (E) of gamba grass hay at three different stages (56, 84 and 112 days of growth) were assessed (Cavalcanti et al., 2016). The highest digestibilities were obtained at the earliest stage (56 days) with 61.87%, 55.69%, 59.17% and 62.5% respectively for DM, CP, CF and E (Cavalcanti et al., 2016). Similar results were obtained with gamba grass hay harvested between 56 and 84 days and had higher in vitro dry matter degradability and nutritional value (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, in vitro dry matter digestibility (IVDMD) of gamba grass silage was the best at 56 days of age (57.28% of DM).
Ensiling can be useful to preserve gamba grass from the reduction of quality during the dry season of tropical savannahs. 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 (Ouachinou et al., 2018).
Supplementation of gamba grass with legumes help to increase the ruminant production from 90-120 to 150 kg live weight gain/head/yr.
Pasture
Cattle grazing on a low fertiliser-input and well managed gamba grass dominated pasture (70–75%) with 727 g/kg NDF and 87 g/kg CP during the rainy season and 737 g/kg and 89 g/kg CP over the dry season, was studied (Ramirez-Restrepo et al., 2019). 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 gained up to 24% more weight than did cull cows when grazing the gamba grass dominated pasture, but cull cows emitted significantly less CH 4 than did old steers (129 vs 141 g/day) on this gamba grass pasture. Live weight gain could be improved when cattle grazed gamba grass in combination with legumes (Ramirez-Restrepo et al., 2019).
Hay
Gamba grass hay was offered to White Fulani heifers at three levels of feeding during the wet season and the dry season (regrowth) (Zemmelink et al., 1972). The hay DM intake varied from 47.7 to 68.3 g/kg LW0.75. This study suggests that the effect of level of feeding on hay intake was largely independent of the selection for CP and shows that the animals prefer 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. It was shown that the 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
Daily idleness of sheep on different pastures was assessed and showed the highest values were on gamba grass pasture (12.06 hours) which suggested that sheep had lower acceptability and grazing activity on gamba grass pasture (de 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 Panicum maximum (111.6 g LW/d) (Gracindo et al., 2014). This suggested that gamba grass is less adequate for sheep than Brachiaria spp. and Panicum maximum pastures (Gracindo et al., 2014).
Hay
Five tropical forage hays including gamba grass (Andropogon gayanus) were fed to Djallonke sheep so as to measure dry matter (DM) voluntary intake and oragnic matter (OM) digestibility (Kaboré-Zoungrana et al., 1999). DM voluntary intake of gamba grass hay ranged from 68 to 26 g/kg BW 0.75 , OM digestibility ranged from 31% to 56% both parameters depending on the phenological stage. Both parameters had lower values than those obtained for Panicum anabaptistum, Pennisetum pedicellatum, Brachiaria lata and Andropogon pseudapricus hays (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). Moreover, 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, nutrients digestibility, nitrogen utilization and enhanced growth rates of rams (Mbahi et al., 2016).
Silage
Gamba grass silages made at different ages of regrowth (56, 84 and 112 d) were used to evaluate intake, digestibility and methane emission from sheep (Ribeiro et al., 2015a). Gamba grass silage daily DM intake ranged from 51.8 to 57.0 g/ kg metabolic weight and was not influenced by silage age of regrowth, but apparent DM digestibility linearly decreased from 52.6% to 38.0% 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
Grazing goats were observed in three cropping systems consisting in a monoculture of gamba grass (Andropogon gayanus) and two intercropping systems of gamba grass + legumes (de Moura et al., 2020). Gamba grass monoculture had the lowest crude protein (CP) and digestibility, the highest neutral detergent fibre (NDF) content and the longest goats grazing time. The grazing goats daily intake in the monoculture of A. gayanus is 2.7% live weight in DM with an average daily weight gain of 85 g/d. The intake is lower than the value the goats in the mixtures, while the average daily gain did not differ between the cropping systems (de Moura et al., 2020).
Hay
Gamba grass (Andropogon gayanus) 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 (Ibeawuchi et al., 1991). Alkali treatment increased the significantly the goats daily DM intake and improved DM, CP and CF digestibilities. The daily DM intake of goats on gamba grass was 19.43 g/kg metabolic weight (Ibeawuchi et al., 1991).
