Signal grass (Brachiara decumbens) is widely used as a forage in tropical regions.
Palatability
Signal grass is palatable during the vegetative growth stage, but coarse and stemmy growth is not well accepted by livestock (Loch, 1977).
Nutritive value
Reported values for in vivo and in vitro DM and OM digestibility show large variations. For instance in vivo DM digestibility ranges from 54 to 82% of DM (the latter for a 14-day old forage) depending on the stage of maturity and other factors (Loch, 1977). Used in pasture in Guyana in a 3 year trial, DM yield, DM digestibility, OM digestibility and N content of Brachiaria decumbens were higher than those of Digitaria swazilandensis (Xandé et al., 1977). In India, Murah buffalo heifers, fed ad libitum with chopped Brachiaria decumbens, had a higher digestibility of nutrients for Brachiaria decumbens (pre-flowering) compared to Megathyrsus maximus (Sanjiv et al., 1998).
Dairy cows
In Brazil, increasing the daily pasture allowance for dairy cows grazing signal grass from 4 or 8% DM of their live weight did not affect milk production and forage intake (Gomide et al., 2001). In Colombia, Holstein and crossbred dairy cows grazing a Brachiaria decumbens pasture, with controlled access for 1 or 2 hours after each milking to 2 forage legumes (Centrosema macrocarpum or Centrosema acutifolium), had similar milk yields, milk fat, solids-non-fats and protein levels. However, there was a tendency to higher milk production for the crossbred cows in the first month of lactation, which did not persist (Mosquera et al., 1992).
Beef cattle
Most studies on signal grass have been conducted with grazing beef cattle in South America, particularly in Brazil and Colombia.
Pasture
Brazilian studies
In grazing conditions, Brachiaria species are an important grass for cattle production in Brazil. Although satisfying performance has been reported for Brachiaria decumbens, different strategies have been studied to improve output by increased availability of forage and supplementation, including the use of legumes.
Supplementation of signal grass pasture is usually favourable. However, in Holstein-Friesian/zebu heifers grazing signal grass pastures, preliminary supplementation with cottonseed meal had no effect on initial live weight, final live weight, average daily gain and pregnancy rate. DM intake was influenced by previous supplementation, but the effect decreased during the grazing period (Cavalcanti Filho et al., 2004). In finishing Nellore steers grazing signal grass pastures, supplementation with cottonseed meal mixed with soybean hulls gave better performance (carcass weight and yield) than cottonseed meal mixed with maize grain or citrus pulp (Andrade et al., 2015). In growing steers, supplementation at 0.8% of LW with a mixture of maize grain, whole soybeans, soybean hulls and cottonseed meal reduced forage intake and grazing time while increasing daily weight gain (Garcia et al., 2014). In crossbred steers grazing pastures of Brachiaria decumbens in the wet season, supplements such as ground maize grains, maize ears and cobs or ground sorghum, all increased performance, though maize ears and cobs were the most effective (Paulino et al., 2005). In young Limousin-Nelore bulls, supplementation with a mineral mix, urea and combinations of cracked maize, soybean meal and wheat bran increased DM intake, DM digestibility and average daily gains compared to animals supplemented with the sole mineral mix (Santos et al., 2004a). Growing steers supplemented with a mixture of cottonseed meal with either maize and cob with husks, cassava meal or soybean hulls did not show differences in performance, but cassava meal resulted in the best economic efficiency (Garcia et al., 2004). Some studies of supplementation have been less positive. Santa Gertrudis calves grazing on Brachiaria decumbens supplemented with a mixture based on soybean meal showed a significantly higher average daily gain in the dry season, but not during the wet season (Coutinho Filho et al., 2005).
Supplements may help to compensate specific deficiencies that occur when grazing Brachiaria decumbens. When crossbred dairy calves reared on a sulphur-deficient pasture of Brachiaria decumbens were fed a basal-supplement containing minerals, urea and maize, with or without added sulphur, the sulphur-supplemented calves had a higher weight gain and a better body condition score than unsupplemented calves, who exhibited a loss of weight and body condition, retarded growth, and slight apathy (Ortolani, 2001).
Holstein-Zebu dairy heifers grazing on deferred pastures of signal grass gained weight when the deferral period lasted 95 days and lost weight when the deferral lasted 140 days (Teixeira et al., 2014).
Colombian studies
In growing Zebu and Zebu x San Martinero bulls, supplementation with sugarcane and the forage legume Cratylia argentea gave better weight gains where animals were grazing fertilized signal grass than when they were supplemented in a corral. Grazing animals also gave better results with supplementation than without (Rincon, 2005). In Romo and Zebu x Romo steers, pastures of mulato grass (Brachiaria ruziziensis x Brachiaria brizantha) gave higher DM yields and supported higher meat yield and weight gains than pastures of Brachiaria decumbens (Cuadrado et al., 2005).
Hay
In steers, a diet of signal grass hay mixed with soybean meal was compared with signal grass hay treated with either NH3 or urea. It was concluded that NH3 and urea treatments of the hay were not economically viable (Fernandes et al., 2002).
Beef cows
In Brazil, Nelore cows grazing Brachiaria decumbens pastures, on a soil improved with limestone and fertilizer, and with free access to a mineral mixture, maintained good reproductive indices (pregnancy, calving and weaning rates) and productivity (weight of calves per ha) over four years (Vieira et al., 2005).
Sheep
In Brazil, giving whole cottonseeds (up to 49% of the diet) to sheep fed a basic diet of Brachiaria decumbens hay did not affect NDF digestibility (Teixeira et al., 2005).