Stephen B. Smith Department of Animal Science Texas A&M University The Main Points of This Presentation Certain production systems promote the development of marbling in beef cattle. A limited number of breed types seem to marble well even when fed limited amounts of concentrate. The Importance of Oleic Acid Beef palatability is positively correlated with the amount of oleic acid in beef. Asian markets prefer beef that contains elevated oleic acid (softer fat). Oleic acid has positive health benefits. The concentration of oleic acid is positively correlated with marbling scores. Monounsaturated:Saturated Fatty Acid (MUFA:SFA) Ratios in Ground Beef Grass-fed beef MUFA:SFA ratios are approx. 0.70. The cheapest ground beef has MUFA:SFA ratio around 0.9. Angus-branded products have MUFA:SFA ratios over 1.2. Wagyu ground beef has a ratio of 1.4. Overview of marbling development USDA Choice Japanese B5 Marbling is composed of fat cells that lie between muscle fibers. Marbling adipocytes Muscle fibers Moody and Cassens, 1968 Differentiation of preadipocytes is accompanied by an increase in stearoyl-CoA desaturase (SCD) gene expression. Chung et al., 2007 CLA t10,c12 strongly inhibited SCD gene expression, but CLA c9,t11 was without effect. Marbling Adipocyte Differentiation SCD gene expression increases. Proliferation Fibroblasts Preadipocytes Mature adipocytes Adipose tissue growth and fatty acids 8 mo old – High in saturated fat 16 mo old High in oleic acid 12 mo old More oleic acid, less saturated fat What production factors influence oleic acid and trans-fatty acid concentrations? Feeding grain-based diets elevates oleic acid and depresses trans-fatty acid concentrations. Increasing time on feed elevates oleic acid and decreases trans-fatty acid concentrations. Feeding corn increases oleic acid and decreases trans-fatty acids. Smith et al. 1998 Archibeque et al. 2005 Chung et al. 2006 12 Corn feeding stimulates stearoylCoA desaturase (SCD) gene expression. Corn feeding depresses the production of transfatty acids in the rumen. Vaccenic acid (18:1trans-11) 10 8 6 4 2 0 20 25 30 35 40 45 Oleic acid (18:1n-9) 50 55 60 Increasing Oleic Acid in Beef Strategies: Genetics and Production We use either good quality Angus or American Wagyu. Low-oleic Pasture-fed Mid-oleic Corn-fed to market weight High-oleic Corn-fed, long-fed Comparisons of Angus and American Wagyu steers. Angus steers consistently produce highquality beef. Wagyu steers are known for their ability to marble. Japanese Black cattle are derived from the Korean Hanwoo. J. Black Korean Black Hanwoo Both breed types are highly marbled and their beef is high in oleic acid. Korean Hanwoo Most of what I know about J. Black cattle I learned from Dr. Meiji Zembayshi. Feeding high concentrate at the end of production increases marbling in J. Black cattle. Dr. Zembayashi described differences between J. Black and other breed types raised in Japan. Cattle containing J. Black genetics contain more marbling than other breed types. There seems to be no limit to the amount of marbling in J. Black cattle. Percentage intramuscular lipid 30 20 B BHo BBHo RBHo CBHo NBHo 10 0 400 600 800 Slaughter age , d 1000 1200 Japanese Black cattle have the highest percentage oleic acid in their fat. 75 “Marbling and fat composition are 60% genetics and 40% production.” Shogo Takeda, Takeda Farm Co., Ltd, Hokkaido, Japan Percentage 70 65 ---Fed for 550 days--- 60 55 Fed for 150 days 50 45 J. Black Wagyu Angus Cattle type Angus X Hereford Higher marbling scores are associated with more monounsaturated fatty acids. Short-fed cattle are low in marbling (%IML) and MUFA. Long-fed cattle are high in marbling and MUFA. This is caused by corn in the diet. Finishing diets: Corn-based diet 89.1% dry matter 11.2% crude protein NEm = 1.81 Mcal/kg NEg = 1.19 Mcal/kg Target = 1.36 kg/d ADG. Hay-based diet Steers had free access to hay and pasture. Corn diet was added to provide 0.9 kg/d ADG. Angus and Wagyu steers were fed cornor hay-based diets. Cattle were sampled at 500 or 600 kg BW. Hay-fed steers were fed an additional 4 mo to match the body weights of the corn-fed steers. Body weights for corn- and hay-fed Angus steers were identical. Corn-fed Wagyu steers grew more slowly than predicted. At 600 kg, hayfed and cornfed steers were at the same body weights. Therefore, all comparisons can be made at equal body weights. Corn- and Hay-fed Angus and Wagyu Steers Marbling increased with body weight. Wagyu steers had higher marbling scores than Angus steers. Corn-fed steers had higher marbling scores than hay-fed steers. SCD gene expression in s.c. adipose tissue was depressed in the hay-fed Angus steers, but increased over time in the Wagyu steers. MUFA:SFA Ratio and Body Weight The MUFA:SFA ratio increased with body weight. Wagyu steers had higher MUFA:SFA ratios than Angus steers. Corn-fed steers had higher MUFA:SFA ratios than hay-fed steers. Factors Influencing Lipid Melting Points Melting points of beef lipids decrease with time on feed. Corn feeding reduces melting points. Less stearic and trans- vaccenic acid is absorbed from the rumen. There is greater desaturase activity in adipose tissues, so there is more oleic acid. Calf-feeding and yearling-feeding When corn is inexpensive or there is not good pasture, producers feed corn to calves as soon as they are weaned. When corn is expensive or there is good pasture, producers background their calves on pasture until they are yearlings (12 mo of age). Carcass and fatty acid composition of calf-fed and yearling-fed Angus steers Calf-fed steers were fed a corn-based diet at weaning at 8 mo Yearling-fed steers grazed on pasture until 12 mo of age. At 12 mo of age, yearling-fed steers were fed the corn-based diet. Steers were sampled at the same time on feed and same body weights. Fat thickness and marbling scores Fat over the loin was higher in calf-fed steers at 12 mo of age. Marbling scores also were higher in calf-fed steers at 12 mo of age. SCD mRNA and MUFA in s.c. fat SCD mRNA in s.c. fat was higher in calf-fed steers at 12 mo of age. The s.c. fat MUFA:SFA ratio also was higher in CF steers at 12 mo of age. SCD mRNA and MUFA in marbling fat SCD mRNA in marbling was higher in calf-fed steers at 12 mo of age. The marbling MUFA:SFA ratio was depressed in yearling-fed steers. Conclusions: Increasing the amount of marbling in beef is related to fatty acid composition of beef. Only a limited number of breed types will marble well on high-roughage, lowconcentrate diets.