Authors evaluated a new beef production system using the rearing by year-round outdoor grazing on improved pastures and fattening by self-sufficient feed of primarily corn silage for Japanese black (JB) steers born in the same bull pedigree. JB steers were grazed outdoors in a year-round on Guineagrass (summer-autumn) and Italian ryegrass (winter-spring) pastures until they reached 539.1±15.3 kg of body weight (BW). The steers were then fed indoors, mainly with corn silage supplemented with commercial formula feed, until they weighed about 714.7±4.1 kg of BW. Total amount of commercial formula feed (wet basis) were 1,115.8±68.2 kg/head (daily: 6.1±0.1 kg/head) during the fattening (F) period, and ratio of corn silage was 31.1±1.5% (dry basis). Daily weight gain (DWG) of the JB steers was 0.95±0.02 kg/day during the F period. In plasma composition during grazing and F periods, alanine aminotransferase, total cholesterol, retinol, β-carotene and α-tocopherol contents decreased (
P<0.05 or 0.01) during the F period from grazing period. After slaughter, the carcasses of the JB steers were graded variably as A-3 (
n=1), A-2 (
n=3) and B-2 (
n=3). Shear-force value of
longissimus thoracis (LT) muscle was 2.2±0.1 kg. Lipid content of the LT muscle was 16.3±1.3%, while type I muscle fiber composition was 30.1±2.7%. Our results indicated that JB steers reared by year-round outdoors on improved pastures showed 0.95 kg/day of DWG fed by corn silage of 30% in dry basis with concentrates during F period. However, there were variations in vital reactions, in particular meat grade, as well as in meat quality, as determined by carcass grading of JB steers produced under the present new feeding system.
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