A Nutritional Survey of Commercially Available Grass-Finished Beef

Abstract

Consumer interest in the source of their food, its environmental footprint, and the impact of diet on health has supported the growth of the grass-finished beef (GFB) industry. Studies have concluded that GFB has distinct nutritional differences from conventionally-finished beef. As the GFB industry continues to expand, it is vital to continue to explore the nutritional complexities and variation in the product. To achieve this, a survey of grass-finishing production systems throughout the USA was conducted, and beef finished on the participating farms was analyzed for its nutritional composition, including fatty acid (FA), mineral and fat-soluble vitamin contents. Samples were analyzed from 12 producers and annual production capacity of farms ranged from 25 to 5,000 cattle, with a mean age of cattle at harvest of 26.8 ± 2.30 mo. An array of finishing diets included grazing exclusively in perennial pasture, incorporating annual forage crops, and feeding a variety of harvested forages with supplementation of non-starch feed byproducts. Beef muscle tissue FA content was analyzed by gas chromatography-mass spectrometry (GC–MS). The mean ratio of omega-6 (n-6) to omega-3 (n-3) FA in samples varied significantly by producer, ranging from 1.80 to 28.3 (P < 0.0001), with an overall sample set median of 4.10. A selection of minerals including iron, magnesium, and potassium were analyzed by ICP emission spectroscopy and mineral content significantly differed by producer for all minerals (P < 0.001). Mean α-tocopherol and β-carotene content was 610.6 µg/100 g beef and 32.2 µg/100 g, respectively. The amount of these antioxidants also varied between producers (P < 0.0001), but tended to be greater in beef finished solely on fresh forages. This survey indicates that commercially available GFB can vary in nutritional composition due to the diverse practices used to grass-finish cattle.

Seasonal differences exist in the polyunsaturated fatty acid, mineral and antioxidant content of U.S. grass-finished beef

“…Producer comparisons of beef cattle by region, finishing diets and age at harvest are summarized in Table 1. Producers are related to a previous study by Bronkema et al and the producer numbers match those in that study [7]. The cattle age at harvest for all four producers ranged between 23 and 28 months.…”

“…Previous research from our group demonstrated that GFB nutritional content varies significantly by producer/production system [7]. Variations in mean total n-6 and n-3 FAs contributed to a 20-fold range in observed n-6 to n-3 ratios (1.80 to 28.3) with some reported ratios much higher than previously suggested for GFB.…”

“…The potential healthfulness of GFB is one of the primary drivers of consumer interest in the product [29]. Research on GFB has mainly focused on its low ratio of n-6 to n-3 FAs [4,7,13,22]. A 2:1 n-6 to n-3 dietary ratio is considered ideal [30], however, typical 'western diets' are estimated to be 20:1 and grain-finished beef have reported ratios up to 13.6:1 [31,32].…”

“…The samples analyzed in this study were cut from the anterior portion of the strip loin (IMPS/ NAMP 180 Beef Loin, Strip Loin). Twelve producers submitted samples for nutrient analysis, as previously described [7]. Samples harvested in the fall were collected between September 2016 -February 2017 and spring harvested samples were collected between June 2017-August 2017.…”

“…All solvents were analytical grade and purchased from Sigma-Aldrich (St. Louis, Missouri, USA). Beef amples were analyzed for mineral, antioxidant and fatty acid content as detailed previously [7]. Briefly, a microwave assisted extraction method was used to extract FAs from 400 mg of beef samples by heating samples at 55˚C for 15 mins in 8 mL of a 4:1 (v/v) solution of ethyl acetate: methanol containing 0.1% (w/v) butylated hydroxytoluene.…”