The deposition of i.m. fat, or marbling, in cattle is recognized as a desirable carcass trait in North American beef grading schemes. In order to investigate the relationship between degree of marbling and fatty acid composition of whole bovine muscle, we extracted the total lipid from pars costalis diaphragmatis (PCD) (n = 23) and longissimus (n = 36) muscles from Wagyu crossbred cattle that were assigned Canadian Grading Agency marbling scores ranging from 1 to 8 on an inverse 10-point scale (i.e., a score of 1 indicated "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. Marbling scores were negatively associated with total lipid from both PCD (r = -.57, P < .01) and longissimus (r = -.80, P < .001). Differences between PCD and longissimus were found for almost all FAME studied from both lipid fractions, but no differences (P > .05) were seen when the monounsaturated:saturated fatty acid (MUFA/SFA) ratios were compared. Heifers had higher (P < .05) oleic acid content and lower (P < .05) palmitic acid content in lipid extracted from both muscles, resulting in higher (P < .05) MUFA/SFA ratios than those for steers. The relative amount of myristic acid increased as the lipid content (total lipid and triacylglycerol) increased in either longissimus (r values from .48 to .55; n = 36; P < .01) or PCD muscles (r from .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 chemical 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 association was not significant (P > .1) for either muscle when linoleic acid from the triacylglycerol fraction was examined, suggesting the negative association 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 variation between animals displaying various degrees of marbling and worthy of further investigation to better understand the process of marbling fat deposition in beef cattle.

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Relationship of plasma leptin concentration to intramuscular fat content in beef from crossbred Wagyu cattle. Can. J. Anim. Sci. 81: 451-457. Plasma leptin concentrations and beef cattle carcass characteristics in eight Continental Crossbred steers [0% Wagyu Cattle (WC)] were compared to crossbred cattle with 50 and 75% WC (eight steers each) genetic makeup to determine if a relationship exists between plasma leptin concentrations and intramuscular fat content (marbling) in beef cattle. Plasma leptin concentrations were measured at two stages of cattle growth, 16 and 4 wk prior to slaughter (WPS). Beef cattle characteristics including marbling score, ribeye area, i.m. total lipid content, and backfat depth were determined, and correlation coefficients obtained between these traits and leptin concentration at both sampling dates. Plasma leptin concentrations increased relative to the lipid content in the 24 steers based on the significant positive correlation observed between plasma leptin and total lipids (% wet weight) from both pars costalis diaphragmatis (p.c. Key words: Wagyu crossbred cattle, meat quality, intramuscular fat, marbling, leptin Wegner, J., Huff, P., Xie, C. P., Schneider, F., Teuscher, F., Mir, P. S., Mir, Z., Kazala, E. C., Weselake, R. et Ender, K. 2001. La relation du niveau de leptin de plasma à la teneur en graisse intramusculaire en bovins croisés de Wagyu. Can. J. Anim. Sci. 81: 451-457. Des niveaux de leptin de plasma et les caractéristiques de carcasse de bovins dans le métis continental (0% Wagyu (WC), 8 bouvillons) ont été comparés aux bovins croisés avec 50 ou 75% Wagyu (8 bouvillons chacun) pour déterminer si un rapport existe entre les concentrations de leptin de plasma et la teneur en graisse intramusculaire (marbrer) dans la viande bovins. Des niveaux de leptin de plasma ont été mesurés à deux étapes de croissance de bétail 16 et 4 semaines avant l'abattage (WPS). Des caractéristiques de bovins comprenant l'indice de marbrure, la zone de ribeye, le contenu total de lipide, et la profondeur de gras du dos ont été déterminées et des calculs de corrélation ont été exécutés. Les concentrations de leptin de plasma ont augmenté relativement au contenu de lipide car il y avait des corrélations positives significatives observées entre les lipides totaux (% de poids humide) et le leptin de plasma pour les pars costalis diaphragmatis (16 WPS: r = 0.69, P = 0.0004; 4 WPS: r = 0.35, P = 0.104) et les muscles longissimus (16 WPS: r = 0.59, P = 0.002; 4 WPS: r = 0.51, P = 0.011). On observe une tendance variable à 4 WPS quand les différentes croix sont comparées. Le leptin de plasma est franchement corrélé pour le 0% Wagyu (longissimus: r = 0.62, P = 0.103; p.c.d.: r = 0.40, P = 0.410), est presque zéro pour les bovins de 50% Wagyu (longissimus: r = 0.11, P = 0.797; p.c.d.: r = 0.005, P = 0.990), et démontre une corrélation négative pour les 75% WC (longissimus: r = -0.60, P = 0.120; p.c.d.: r = -0.65, P = 0.164). Les résultats suggèrent que cela la génétique croissante de Wagyu viole n'impo...

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Production of dairy products with increased amounts of nutraceutic FA such as conjugated linoleic acid (CLA) represents a recent approach for dairy producers and processors to increase the value of their products. The effect of CLA and other FA on the expression of diacylglycerol acyltransferase-1 (DGAT-1) and DGAT-2, and DGAT activity were investigated in bovine mammary gland epithelial (MAC-T) cells. DGAT gene expression analyses were also conducted using bovine mammary gland tissue from dairy cows. In the studies with MAC-T cells, there were no significant effects of CLA isomers or other FA on DGAT1 expression, whereas all FA tested showed enhanced DGAT2 expression (P < 0.05 to P < 0.001), with alpha-linolenic acid (alpha-18:3) having the greatest effect. Additionally, DGAT2 expression was co-ordinated with expression of lysophosphatidic acid acyltransferase (LPAAT), an observation that was also apparent in mammary gland from lactating dairy cows. In contrast, treatment of MAC-T cells with trans-10, cis-12 18:2 or alpha-18:3 resulted in a significant (P < 0.05) decrease in overall DGAT enzyme activity, although the mechanisms resulting in these effects are unclear. Competition assays using microsomes from bovine mammary gland tissue and 1-[(14)C]oleoyl-CoA suggested that DGAT activity was more selective for oleoyl (cis-9 18:1)-CoA than cis-9, trans-11 18:2-, trans-10, cis-12 18:2- or cis-9, cis-12 18:2-CoA. Collectively, the results suggest the relationship between trans-10, cis-12 18:2 and reduced TAG production in bovine milk is not linked to the production of DGAT1 or DGAT2 transcripts, but probably involves effects of this CLA isomer at events beyond transcription, such as post-translational and/or enzyme activity effects.