Effects of Breeds and Nutritional Planes on Intramuscular lipid Deposition of Fattening Steers

Abstract

Intramuscular lipid content in eight muscles from every Japanese Black steers of 2 strains, which differed mainly in growth potential, 31 and 35 heads respectively, and Holstein steers of 16 heads, and also in 7 muscles from every 37 Japanese Shorthorn steers, were analized by extracting method using diethyl-ether. Intramuscular lipid content in the muscles of Japanese Black were greater than the other two breeds, but the differences of that content between Japanese Shorthorn and Holstein, and between 2 strains of Japanese Black were not significant. Lipid contents in almost all muscles of Japanes Black fattened on medium-high nutritional plane were higher than those fattened on high plane. But, in the case of Japanese Shorthorn, the difference between the two nutritional planes was not significant in all muscles. As the relative growth coefficients of intramuscular lipid weight to total dissected carcass fat weight were not greater than 1.0 in almost all muscles of all breeds, the growth of intramuscular lipid is seemed to mature earlier than that of carcass dissectable fat. The lipid deposition in muscles are positively related to the degree of fat deposition in carcass, but as the variation of intra-muscular lipid content among cattle were large, especially in case of Japanese Black and Holstein, it is dificult to estimate the degree of intramuscular lipid deposition by the fatness of cattle. To estimate intramuscular lipid content in M. longissimus thoracis, maturity ratio, slaughter age and total dissected fat percentage of steer were used as independent variables for stepwise regression procedure. The variables which entered into the model at the 0.15 significance level differed mainly according to the nutritional plane and/or carcass fat deposition levels. In the case of fast grown steers fattened on high plane, slaughter age was the main variable and in the case of rather long term fattened steers on medium-high plane and/or steers which had rather low carcass fat percentages as Holstein fattened even on high plane, total dissected carcass fat percentage was the main variable in every breed, respectively.