Dried distillers grains with solubles (DDGS) are widely used in North American feedlot rations. Feedlot operators can quickly and easily calculate the impact of DDGS on animal performance and carcass grade, but determining how DDGS might affect retail beef quality is much more diffi cult and expensive. Feeding DDGS may increase polyunsaturated fatty acid (PUFA) levels in beef. This could have human health benefits. For example, omega-3s are a type of PUFA. Health Canada could allow a nutrient content claim for beef that contains at least 300-mg omega-3s per 75-g serving. However, PUFAs are less oxidatively stable than saturated fats. This makes PUFAs more prone to chemical reactions that lead to off-flavours, unpleasant smells, discolouration and shortened shelf life. Two recent National Check-Off funded research projects investigated how feeding DDGS affects PUFA levels (including omega-3s) and retail acceptability of beef.
What they did
In Trial 1, Drs. He, Yang, McAllister and Beauchemin of Agriculture and Agri-Food Canada s Lethbridge Research Centre worked with Dr. John McKinnon at the University of Saskatchewan. These researchers used DDGS to replace barley silage in the finishing diet. A total of 200 crossbred steers were fed four diets (20 pens, 10 head per pen, five pens per diet). The control diet contained 85 per cent barley-based concentrate and 15 per cent barley silage. One experimental diet replaced some of the barley grain with wheat DDGS (65 per cent concentrate, 10 per cent silage, 25 per cent wheat DDGS). The other two experimental diets replaced silage with wheat DDGS. These two diets both contained 65 per cent concentrate, and either five per cent silage (30 per cent DDGS) or zero silage (35 per cent DDGS). The percentage of intramuscular (marbling) fat was determined in skirt steaks, as well as the percentage of PUFA and omega-3s.
In Trial 2, Dr. John McKinnon partially replaced barley grain with DDGS in a finishing trial at the University of Saskatchewan. A total of 288 crossbred steers were finished on four diets containing 93 per cent barley-based concentrate and seven per cent barley silage (24 pens, 12 head per pen, six pens per diet). The control diet contained no DDGS. The three experimental diets replaced some of the barley grain with 40 per cent corn DDGS, 40 per cent wheat DDGS, or 40 per cent DDGS from a corn/ wheat blend. At the end of the trial, Dr. Phyllis Shand and graduate student Lane Stoll collected rib-eye steaks from 20 head per diet, aged them for 14 days and did intramuscular fat analyses, shelf life and taste panel tests.
What they learned
Trial 1: Replacing silage with DDGS in the finishing diet did not affect intramuscular fat (marbling) levels in the skirt steak. The PUFA levels rose as the DDGS content of the diet increased, but still accounted for less than seven per cent of the total intramuscular fat. Omega-3 levels also rose along with the DDGS content of the diet, but were still below 40 mg per serving. These levels would have to be eight to 11 times higher to meet Health Canada labelling standards.
Trial 2: Replacing 40 per cent of the barley grain with DDGS in the finishing diet didn t affect intramuscular fat (marbling) levels in the rib-eye. PUFA levels were higher in the 40 per cent DDGS diets (11.3 to 12.2 per cent of total intramuscular fat) than in the barley grain control diet (seven per cent). Diet also affected omega-3 levels, but were well below 15-mg per serving, and would have to be 25 to 33 times higher to meet Health Canada labelling standards.
Compared to steaks from cattle in the control group, steaks from cattle fed the DDGS diets were less red, lost redness faster, showed more discolouration and were less desirable to consumers as time in the display case increased. Recall that these steaks had been aged for two weeks prior to entering the retail case, so this may not be a serious concern in all retail situations.
Diet did not significantly affect the fat content, drip loss, cooking loss, cooking time or sheer force (a mechanical measure of toughness) of rib-eye steaks.
Taste panel evaluation
The trained taste panel did not detect any significant differences in tenderness, juiciness, flavour, or texture of the rib-eye steaks from cattle fed the four different diets.
What it Means: Feeding DDGS increased the omega-3 and overall PUFA levels in beef. Although omega-3 levels are still far from meeting Canadian regulatory standards, PUFA levels may be elevated enough to increase the risk of oxidation and negatively affect the appearance of beef that has been aged before entering the retail meat case. Once the beef is cooked, however, there do not appear to be any differences in eating quality in the beef from cattle fed diets containing DDGS compared to those fed traditional feedlot finishing diets.
ReynoldBergenisthesciencedirectorfortheBeefCattle ResearchCouncil.Onaverage,15percentofCanada s NationalCheckoffisdirectedtowardstheBCRCtofund researchanddevelopmentactivitiesthatwillimprovethecompetitiveness andsustainabilityofCanada sbeefindustry.For moreinformation,visit www.cattle.ca orcall403-275-8558.