Nutritional composition of beef: a comparison of commercial North American grass- and grain-finishing systems

Beef's fatty acid and mineral profile is influenced by finishing diets, yet the nutritional variability within both grass- and grain-fed beef samples from commercial operations remains underexplored. Understanding potential differences is important for producers and consumers. This study profiled grass- and grain-fed beef from commercial North American producers and retailers, and evaluated relationships among grazing practices, forage quality, soil characteristics, and beef fatty acid and mineral composition. Beef samples (grass-fed, n = 253; grain-fed, n = 84), along with forage and soil samples where possible, were collected from 108 commercial producers and retailers. Fatty acids were analyzed using gas chromatography-flame ionization detection (GC-FID), and minerals were quantified using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Statistical models evaluated differences and correlations between and within finishing practices using Welch's t-test and Pearson's correlation analysis. Grass-fed beef had a lower omega-6:3 ratio (2.14 vs. 8.28, P < 0.001) and higher concentrations of the fatty acids alpha-linolenic acid (ALA; 0.99 vs. 0.27%), eicosapentaenoic acid (EPA; 0.28 vs. 0.07%), docosapentaenoic acid (DPA; 0.41 vs. 0.17%), conjugated linoleic acid (CLA; 0.49 vs. 0.31%), and the minerals calcium (9.26 vs. 3.08 mg/100 g), copper (0.253 vs. 0.129 mg/100 g), iron (2.29 vs. 1.92 mg/100 g), and selenium (0.012 vs. 0.002 mg/100 g) compared with grain-fed beef (all P < 0.05). However, considerable nutritional variation exists, particularly within grass-finished beef, with omega-6:3 ratios ranging from 0.62 to 11.45. Animals finished on biodiverse pastures exhibited fatty acid profiles characterized by higher omega-3 to total polyunsaturated FA content, resulting in a higher omega balance (r = 0.30, P = 0.02). However, some grass-fed samples, particularly several retail-purchased samples, displayed fatty acid compositions with relatively low omega-3 content, resulting in an omega balance similar to grain-fed beef. These findings highlight the need for clearer guidance on "grass-fed" management definitions and more transparent labeling that reflects measurable nutritional attributes, such as omega-3 content, omega-6:3 ratio, and/or omega balance.