Relationship of fatty acid composition to intramuscular fat content in beef from crossbred Wagyu cattle

The deposition of i.m. fat, or marbling, in cattle is recognized as a desir able carcass trait in North American beef grading schemes. In order to inve stigate the relationship between degree of marbling and fatty acid composit ion of whole bovine muscle, we extracted the total lipid from pars costalis diaphragmatis (PCD) (n = 23) and longissimus (n 36) muscles from Wagyu cro ssbred cattle that were assigned Canadian Grading Agency marbling scores ra nging from 1 to 8 on an inverse 10-point scale (i.e., a score of 1 indicate d "very abundant" marbling and a score of 10 would be assigned to a carcass "devoid" of marbling). Fatty acid methyl esters (FAME) of the total lipid and triacylglycerol fractions were resolved and quantified through GLC. Mar bling scores were negatively associated with total lipid from both PCD (r = -.57, P < .01) and longissimus (r = -.80, P < .001). Differences between P CD and longissimus were found for almost all FAME studied from both lipid f ractions, but no differences (P > .05) were seen when the monounsaturated:s aturated fatty acid (MUFA/SFA) ratios were compared. Heifers had higher (P < .05) oleic acid content and lower (P < .05) palmi tic acid content in lip id extracted from both muscles, resulting in higher (P < .05) MUFA/SFA rati os than those for steers. The relative amount of myristic acid increased as the lipid content (total lipid and triacylglycerol) increased in either lo ngissimus (r values from .48 to .55; n = 36; P < .01) or PCD muscles (r fro m .67 to .76; n = 23; P < .001). The relative amount of linoleic acid (cis- 9, cis-12 isomer) from total lipid was negatively associated with all chemi cal measurements of lipid from the longissimus (r from -.52 to -.64; n = 36 ; P < .001) and PCD muscles (r from -.75 to -.85; n = 23; P < .001). This a ssociation was not significant (P > .1) for either muscle when linoleic aci d from the triacylglycerol fraction was examined, suggesting the negative a ssociation between this fatty acid and lipid content was due to a dilution of membrane phospholipids with increasing triacylglycerol. Indices of fatty acid elongase activity, calculated from FAME data, implicated the balance between this enzyme activity and fatty acid synthase as a source of variati on between animals displaying various degrees of marbling and worthy of fur ther investigation to better understand the process of marbling fat deposit ion in beef cattle.