The utilization of the dietary energy of pangola and setaria by young growing beef cattle

Abstract

The net energy values for growth and fattening of two artificially dried tropical grasses-, pangola {Digitaria decumbens) and setaria (S. sphacelata var. sericea cv. Nandi), of similar estimated metabolizable energy content (8-07 and 7-96 MJ/kg D.M.) were determined with cattle using a slaughter technique. Growing cattle with a mean initial weight of 175 kg were given equal quantities of dry matter of the two grasses at each of three planes of nutrition above maintenance for a period of 152 days.The initial energy, fat and protein content of the total body of the 24 test animals was estimated from regressions relating fasted live weight to thes"e components, derived from 12 similar cattle slaughtered at the beginning of the feeding period. The final energy, fat and protein content of the test animals was determined directly by chemical analysis. The metabolizable energy (ME) content of the grasses was estimated from the level of digestible energy (DE) determined with eight cattle, assuming that ME = 0-815 DE.The cattle fed pangola gained more live weight, empty-body weight, fat, protein and energy than animals fed similar quantities of setaria. The net energy value for growth and fattening (NE f ) was determined using regressions relating energy retention to the quantity of dry matter eaten. NE, in MJ/kg dry matter was 2-27 for pangola and 1-31 for setaria.Efficiency of utilization of ME for growth and fattening (k f ) was .27-7% for pangola and 16-9% for setaria. These values for tropical grasses are lower than any values reported for temperate pasture species. Thus the lower efficiency of utilization of ME may cause the lower production of cattle which graze tropical grasses.It was concluded that as the k, values of different tropical grasses are not constant, k, values should be measured on a wider range of tropical grasses so that this factor can be taken into account when evaluating grasses in animal production systems.

Digestible cell wall and undigested cellular contents of two grasses of low net energy value for growing cattle

“…Arguments advanced by Moir (19726) to explain the constancy of the digested cell wall of grass centred on the time that digesta is retained in the rumen; a forage of high cell-wall content, or one with cell walls highly resistant to degradation in the rumen, would be retained for a longer time than one with readily degradable cell walls. A long retention time was one of several causes suggested by Tudor & Minson (1982) for the low net energy values of their two grasses. With a long retention time, food protein is exposed to deamination that, even in normal circumstances, McDonald (1952) found to be an inefficient process.…”

“…sericea cv. Nandi), details of which have been given by Tudor & Minson (1982). Net energy values determined using a slaughter technique were, respectively 2-27 and 1-31 MJ/kg D.M.…”

Evaluation of pasture for beef cattle from measurements of cell wall in separated leaf and stem fractions

“…Their in vitro digested cell-wall values, in the same run as green leaf of pangola and setaria with in vitro values of around 40%, were, respectively, 34 and 31% of forage OM. Both of these grasses had low efficiencies of utilization of their dietary energy (Tudor & Minson, 1982).…”

Nutrient Requirements of Domesticated Ruminants

“…There is little information on the NE value of tropical forages, but it is known (Norton 1982) that they characteristically contain lesser concentrations of soluble non-structural carbohydrates than temperate forages, and greater concentrations of structural, cell-wall carbohydrates, with the result that there are higher proportions of acetate in the ruminal SCFA. However, attempts to measure k g have given very variable results, partly because of the low rates of gain achieved on the experimental diets (Rees et al 1980;Tudor and Minson 1982).…”