A series of experiments was undertaken to study a Trichoderma longibrachiatum derived exogenous enzyme product, Roxazyme® G2 Liquid (RG2 - DSM Nutritional Products Pty Ltd, Basel, Switzerland) and evaluate its effects on utilisation of grain based diets by ruminant animals. Assays indicated that RG2 contains significant concentrations of endo-1,4-β-xylanase, endo-1,4- β-glucanase, endo-1,3:1,4- β-D-glucanase and β-glycosidase as well as lower concentrations of a-amylase, protease and pectinase. When applied to natural substrates in vitro, RG2 solubilised to the greatest extent barley grain, then pangola grass, sorghum grain and lucerne hay but the rate of solubilisation was the same for all substrates.
High quality lucerne hay chaff was substituted with increasing levels of barley grain in diets fed hourly to crossbred lambs and results showed that increasing grain inclusion raised total tract OM digestibility, but depressed voluntary feed intake. Despite rumen fluid pH levels declining below 6.0 and reductions in the amount and efficiency of microbial N production, increasing grain content did not lower total tract fibre digestibility, likely due to the intrinsic ferment ability of the diets. In sacco incubations in RG2 unsupplemented lambs revealed that 4 and 8 ml RG2 /kg DM application rates increased the extent but not the rate of DM disappearance of barley grain compared to untreated grain, implying some pre-feeding action for the enzyme.
RG2 applied to the concentrate portion of diets containing either circa 60% barley or sorghum grain with pangola chaffed to growing steers increased voluntary feed intake of the sorghum diet by 11% but had no effect on intake of the barley diets, which exhibited high total tract nutrient digestibility. RG2 increased L W gains after 4 weeks of supplementation irrespective of grain type. When applied to the sorghum diet, RG2 caused lower total tract starch digestibility when measured 6 weeks after supplementation commenced and increased urinary N excretion. Comparable but less defined intake responses to RG2 were observed in growing lambs on similar sorghum diets with effects dependant on application rate. Relative to the steers, lambs had higher DM intakes, higher total tract starch digestibility (1 7% units) of the sorghum diet but lower cellulose digestibility on both diets. RG2 treatment did not significantly affect total tract fibre digestibility in either trial, but changes in NH3-N and butyrate concentrations in rumen fluid signified effects at the rumen level.
Fractional passage rates of liquid, grain and fibre associated markers and in sacco incubations of sorghum grain and pangola chaff were used to investigate rumen level RG2 effects in steers fed high (60%) and low (35%) sorghum grain diets. The previously observed intake increases with RG2 were not detected, possibly as the 24- day experimental periods excluded longer-term adaptive responses. RG2 treatment depressed the insoluble potentially degradable fraction of pangola chaff and lowered flow rates of sorghum associated marker on the high sorghum diet while increasing rates on the low grain diet. These rumen level changes were not associated with lower total tract fibre digestibility, which was depressed by higher dietary grain levels, as were passage and digestion rates and fungal colonisation of fibre.
Ninety six steers were commercially fed 72% sorghum grain diets treated with four rates of applied RG2 and measurements of feed intake, utilisation, growth rates and carcase attributes revealed that at high levels of performance there was no effect of RG2 supplementation. A final experiment investigated three rates of RG2 application to barley and sorghum grain supplements fed to grazing, early lactation cows in a sub-tropical dairying system. Cows were increasing in L W and body condition with high daily milk yields (28. 6 L) and RG2 had no significant effect on these measurements or feed intake despite some grain specific rumen fermentation (NH3-N and VFA ) changes. Low dietary fibre levels were associated with low milk fat yields and RG2 application at 4 ml/kg DM concentrate tended to exacerbate this effect.
In conclusion, RG2 supplementation of grain-based diets can produce increased feed intake, without changes in total tract fibre digestibility, but responses depend on the means by and extent to which nutrient availability and use is limited, as well as the amount of RG2 supplied. RG2 supplementation did not produce consistently positive production responses and therefore cannot be recommended for sheep, beef cattle or dairy cattle fed barley or sorghum grain-based diets.