Effects of composition rate of rumen degradable protein (RDP), barley [Hordeum vulgare] and corn [Zea mays] on the fattening performance and the meat quality of crossbred steers after the middle period

We examined the combined effects of composition rate of rumen degradable protein (RDP). Barley and corn in feed during the middle period (14.6-19.2 months of age) and the latter period (-25.1 months of age) on fattening performance and meat quality, using eighteen cross-bred steers. The comparative study was carried out by grouping the subject steers into four groups; four combinations of two proportions of RDP (61.6 - 66.7% as higher level and 55.8-59.7% as lower level) in crude protein (CP) and two different rates of barley and corn content (mainly-barley and mainly-corn), keeping constant the amount of total digestible nutrition (TDN) and CP. Feed intake increased significantly in the lower level RDP fed groups both in the middle and the latter periods. The daily gain tended to increase in the lower level RDP fed groups in the middle period and body weight also increased in the latter period, significantly. Concerning meat quality, interaction effects were observable, and with regard to the Beef Color Standard (BCS No.), the combination of high level RDP and mainly-corn fed group registered the highest number among the four groups. Furthermore, interaction effects were observed also on the rate of oleate content in total fatty acids of longissimus thoracis muscle lipid. The rate of oleate content was higher in the mainly-barley fed group under the condition of lower level of RDP, while there was no difference between the mainly-barley fed group and the mainly-corn fed group under the condition, higher level of RDP having been fed. These results suggest that an increase in weight of the dressed carcass can be expected by feeding 56-60% of RDP in CP and that the color of meat and the rate of oleate in fatty acids of longissimus thoracis muscle lipid can be controlled by the proportion of RDP, barley and corn.