Pasture-finishing of cattle in Western U.S. rangelands improves markers of animal metabolic health and nutritional compounds in beef

As environmental and health concerns of beef production and consumption mount, there is growing interest in agroecological production methods, including finishing beef cattle on pastures with phytochemically diverse grasses, forbs, and/or shrubs. The goal of this metabolomics, lipidomics, and fatty acid methyl ester profiling study was to compare meat (pectoralis profundus) of Black Angus cattle from two commercial US beef finishing systems (pasture-finished on Western U.S. rangeland; n = 18 and grain-finished in a Midwest U.S. feedlot; n = 18). A total of 907 out of 1575 compounds differed in abundance between pasture-finished and grain-finished beef samples (all, false discovery rate adjusted P < 0.05). Pasture-finished beef contained higher levels of phenolic antioxidants (2.6-fold), alpha-tocopherol (3.1-fold), nicotinate/vitamin B₃ (9.4-fold), choline (1.2-fold), myo-inositol (1.8-fold), and omega-3 fatty acids (4.1-fold). Grain-finished beef contained higher levels of gamma-tocopherol (14.6-fold), nicotinamide/vitamin B₃ (1.5-fold), pantothenate/vitamin B₅ (1.3-fold), and pyridoxine/vitamin B₆ (1.3-fold); indicating that feeding some grain (by-products) could be beneficial to increase levels of certain B-vitamins. Pasture-finished beef samples also displayed lower levels of oxidative stress (homocysteine, 0.6-fold; and 4-hydroxy-nonenal-glutathione, 0.4-fold) and improved mitochondrial function (1.3-fold) compared to grain-finished animals. Two potential metabolites of fluoroquinolone antibiotics, 2,8-quinolinediol and 2,8-quinolinediol sulfate, were only observed in grain-finished beef, though the source remains unknown. While pasture-finished cattle displayed improved markers of metabolic health and concentrated additional, potentially health-promoting compounds in their meat, our findings should not be interpreted as that grain-finished beef is unhealthy to consume. Randomized controlled trials in humans are required to further assess whether observed differences between pasture-finished and feedlot-finished beef have an appreciable effect on human health.