The relative value of concentrates and roughage for fattening cattle

SUMMARY In three similar experiments, 2 or 3 kg of a commercial concentrate mixture, forming part of a high concentrate ration, were replaced by an equal weight of dry matter of one of four roughages: hay, straw, silage and green soilage. The metabolizable energy content of the concentrate was 2-4 Mcal/kg. Expected daily gain was calculated according to the following energy systems: Scandinavian feed units (SFU), starch equivalent (SE), total digestible nutrients (TDN), the U.K. Agricultural Research Council system (ARC), and the U.S. National Research Council net energy system (NRC). The replacement of 2 kg of concentrate significantly reduced daily gain only in the straw treatment. Reduction of the fat content of the carcasses was significant for all roughage treatments. The differences between the observed daily gain and the expected, as calculated by the SFU, SE and NRC systems, were highly significant, while those between the observed and those cal culated by the TDN and ARC systems were not significant. The TDN system overestimated the nutritional value of the roughages, while the SFU and SE systems underestimated it.