Intramuscular fat deposition in principal muscles from 24 to 30 months of age using identical twins of Japanese Black steers

¹ National Livestock Breeding Center, 1 Odakurahara, Nishigo, Fukushima, 961-8511, Japan
² Nippon Veterinary and Life Science University, Musashino, Tokyo 180-8602, Japan
³ National Livestock Breeding Center Ohu Station, Shichinohe, Aomori 039-2567, Japan

^* To whom correspondence should be addressed. E-mail: t0okumur{at}nlbc.go.jp.

	Abstract

The changes in intramuscular fat deposition in principal muscles (M. semitendinosus, M. semimembranosus, M. psoas major, M. latissimus dorsi, M. longissmus (7 to 8^th and 10 to11^th thoracic vertebrae) and M. supraspinatus) from 24 to 30 mo of age were investigated using identical twins of Japanese Black steers. Four sets of identical twins of Japanese Black steers were used in this study. Animals were fattened from 10 to 24 or 30 mo of age for each pair of identical twins. Body weights of twin steers slaughtered at 24 and at 30 mo of age were similar at 10 mo of age and thereafter up to 24 mo of age. The serum concentration changes of vitamin A, glucose, total cholesterol, albumin and total protein were similar in each pair of twins during the first stage (10 to 24 mo). Fat contents of M. longissimus (7 to 8^th) at 24 and 30 mo of age were 37.0% and 42.4% respectively (P < 0.05). Moreover, in the principal muscles except M. semimembranosus and M. supraspinatus, fat content at 30 mo of age was greater than at 24 mo of age (P < 0.05). The proportional increase in fat content from 24 to 30 mo of age was greatest in M. semitendinosus (+ 58.7%) and lowest in M. supraspinatus (+ 6.1%). These results demonstrate that intramuscular fat continues to increase after 24 mo of age, and the rates of intramuscular fat deposition and the ages when intramuscular fat is deposited are different for every muscle.

Key Words: Beef, chemical composition, intramuscular fat, muscles, steers