　交雑種去勢肥育牛(黒毛和種♂×ホルスタイン種♀)21頭を用いて，イタリアンライグラスホールクロップサイレージ(以下，IRWS)の給与期間が肉質に及ぼす影響を検討した。試験は，全期間稲ワラを給与した区を対照区とし，IRWSの給与期間により，生後7～14カ月齢にIRWSを給与した前期区，生後7～19カ月齢にIRWSを給与した前中区および生後7～23カ月齢にIRWSを給与した全期区の3区を設定し，生後23カ月齢に出荷と畜して枝肉検査および牛肉の理化学的性状検査等を実施した。枝肉成績において，前期区，前中区および全期区の肉色と肉締まりは対照区よりも優れる傾向にあった。IRWSを給与した3試験区は，脂肪交雑粒子の形状係数が高く，牛肉中コラーゲンの熱分解性が低い傾向にあった。胸最長筋のリン脂質中脂肪酸組成は，IRWSを給与した3試験区とも対照区に比べてリノール酸割合が低く，リノレン酸は高かった。これらの結果から，IRWSの給与は牛肉中コラーゲン性状や脂肪酸組成に影響し，生後7～14カ月齢にIRWSを給与した時の影響が出荷時まで残ることが明らかとなった。

　Effect of the Period of Feeding Italian Ryegrass Silage on the Meat Quality of Crossbred Steers (Japanese Black×Holstein). KOGA Tetsuya, Sunao INADA and Yoshihiro ISOZAKI (Fukuoka Agric. Res. Cent. Chikushino, Fukuoka 818-8549, Japan) Bull. Fukuoka Agric .Res. Cent.,23: 83- 87 (2004)

　To study the effect of the feeding period of Italian ryegrass silage (IRWS)on the meat quality of crossbred steers(F1), 21 crossbred steers of 7 months old were examined. Based on the feeding period of IRWS, F1 was arranged into four groups. The feed period of IRWS for Group A was from 7-14 months old; Group B,7-19 months old; and Group C,7-23 months old. A control group was fed rice straw without being fed IRWS from 7 to 23 months old. The steers of each group were slaughtered and their meat inspected. When the meat quality of each examination groups (A, B and C) was compared with that of the control group, the color and firmness of the meat of the examination groups were judged superior. The form scores of the marbling particle in ribeye area of the examination groups fed IRWS was more complicated than that of the control. Moreover, the pyrolysis nature of the collagen of meat from former groups was lower. Compared to the control group there was less linoleic acid in the phospholipid of the musculus longissimus thoracis of the examination groups fed IRWS. In fact, there was few linolenic acid.