The comparative value of molasses and grain as energy sources for beef production

Abstract

In the first experiment the liveweicht responses of steers managed under feed lot, semi-intensive und continuous grazing systems were evaluated. Three systems (molasses/urea, sorghum or grazing alone) and three diets (sunflower meal/hay, leucaena/grasss or legume/grass) , two cattle breeds (Hereford or Belmont Red) and two levels of zeranol implantation (0 or 3 6 mg) were used as experimental treatments. Steers fed sorghum grain under feed lot condition exhibited the highest liveweight gain (1.54 kg/d). However, steers fed molasses/urea exhibited low liveweight gain (0.72 kg/d) managed under similar condition. Similarly steers given grain supplementation managed under either semi-intensive or continuous grazing system exhibited higher liveweight gains compared with steers supplementation with molasses/urea. Irrespective of the management system steers supplementation with molasses/urea had significantly (P< 0.05 ) lower dry matter intakes compared with steers supplementation with grain. In continous grazing situation, steers with access to leucaena /grass exhibited lower liveweight gain (0.81 kg/d) than steers supplemented with 2.5 kg of sunflower seed meal (0.91 kg/d). In general, the liveweight gain of steers grazing the B.decumbens was superior to steers grazing the P .plicatulum pasture. The liveweight gain of steers implanted with zeranol not significantly different to control animals. The liveweight gain of both breeds of cattle (Hereford and Belmont Red) in this experiment was similar. The effect of inclusion of sorghum grain into molasses diets on dry matter intake, liveweight gain, nitrogen utilization and volatile fatty acid fermentation patterns in rumen fluid of steers was invest.gated in the second experiment. Inclusion of small amounts of grain (33%) into molasses resulted in a significant (P<0.05) increase in dry 0 7 5 matter intake (from 9 6 to 127g/kg 0.75 /d) , liveweight gain (from 543 to 965g/d), apparent nitrogen retained (from 22.3 to 62.4%) and percentage of propionic acid concentration (from 15 to 22.2%) in rumen fluid of steers. Formaldehyde treatment of cereal grain resulted in decreased volatile fatty acid and ammonia production in the rumen fluid in-vitro. In a subsequent experiment the effect of formaldehyde treatment of sorghum and pigeon pea (3g formaldehyde /100 g CP) grain on liveweight gain on lambs was eveluated. Subsequently the efficacy of formaldehyde treatment of grain (wheat and sorghum) on the extent and the sites of digestion of starch and protein in sheep was investigated. Sheep fed formaldehyde treated sorghum grain showed higher liveweight gains (122 g/d) when compared with sheep fed untreated grain (61 g/d). Formaldehyde treated wheat or sorghum fed to sheep fitted with ruminal and abomasal canulae showed a significant increase in microbial nitrogen (78 and 76% for wheat and sorghum) and starch (46 and 55% for wheat and sorghum) flow from the stomach. Although the total organic matter flow from the stomach was not significantly different between the treated and untreated grain, the amount of non-microbial organic matter flow to the intestine of sheep given treated grain was significantly higher than that for sheep given untreated grain.Cattle fed formaldehyde treated sorghum grain (3g formaldehyde/100 g CP) under feed lot conditions had similar liveweight gains (1.16 kg/d) to steers fed untreated grain (1.24 kg/d). Inclusion of sodium bentonite in the feed (at 2 or 4%) had no effect on either dry matter intake or liveweight gain of steers. Grain and molasses/urea fed to cattle, sheep and goats showed that animals fed grain had higher dry matter intake, nitrogen retention and liveweight gain than did those fed molasses/urea diets. However, cattle given the molasses diet exhibited significantly higher molar percentage of butyric acid (41.7%) and lower percentage of propionic acid (15.1%) in the rumen fluid compared with sheep and goats (6.2 and 30.2% butyric and propionic acid respectively) given the similar diet. Bucks fed grain diet exhibited higher liveweight gain (7 0 9 g/kg 0.9 /d) , feed conversion efficiency (6.4) and apparent 0 9 nitrogen retention (55.3%) than did does (5 g/kg 0.9 /d, 9.0, 29.4% liveweight gain, feed conversion efficiency and percentage apparent nitrogen retained respectively) given the similar diet. However, no significant differences in liveweight gain and nitrogen retention was recorded between wethers and ewes.Finally the effect of supplementation with either grain (1.1 kg/head/d) plus sunflower meal, sodium propionate (65 g/head/d) plus sunflower meal or sunflower meal plus intraabomasal infusion of glucose (200 g/head/d) of steers given molasses plus sunflower meal diet was examined. Steers given grain or propionate supplements exhibited significantly (P<0.05) h igher liveweight gains (933 and 898 g /d respectively) compared with steers given molasses plus sunflower meal (703 g/d). Steers given either grain, propionate supplements or glucose infusion exhibited higher percentage of apparent nitrogen retention (37.9, 35.7 and 37.2 respectively), 0 7 5 glucose entry rates (15.6, 13.9 and 16.9 g/kg 0.75 /d respecively) , plasma insulin concentrations ( 64.5, 48.8 and 69.8 mU/L respectively compared with steers given molasses plus sunflower meal ( 18.5 %, 12.1 g/kg0.75/d and 20.5 mU/L for apparent nitrogen retained, glucose entry rate and plasma insulin concentration respectively). The plasma urea nitrogen concentrations of steers given either grain, propionate supplement or intra-abomasally glucose infusion of steers (37.6, 40.3 and 35.9 mg/L respectively) were significantly (P<0.05) lower than did steers given molasses plus sunflower meal (59.8 mg/L).It was concluded from these studies that inclusion of small amounts of grain (1.1 kg/head/day) in molasses diets resulted in increased dry matter intakes and rumen propionic acid concentrations which in turn resulted in increased supply of glucose to the tissues and*thus sparing amino acids resulted in increased nitrogen retention and higher growth rate of steers.