While there are concerns regarding the effects of red meat consumption on non-communicable diseases and climate change, this view does not consider the impact of different production practices. Grass-finished beef (GFB) generally aligns with the demands of consumers who are concerned about nutrition and the environment. GFB usually contains higher levels of omega-3 polyunsaturated fatty acids (n-3 PUFAs), conjugated linoleic acid (CLA), vitamin E, and phytochemicals desired by health-conscious consumers. However, a recent survey of commercially available GFB found large variations in the nutritional profile of beef coming from different producers. In some cases, GFB had a higher omega-6:omega-3 (n-6:n-3) ratio than grain-finished beef. This dissertation aims to explain nutritional variations in GFB and investigate the influence of breed and feeding practices on its composition including fatty acids (FAs), micronutrients, and phytochemicals. In the first study, Red Angus (RA) and Red Angus x Akaushi (AK) steers (n = 104) were randomly allocated to either a pasture or a grain diet. Feed samples were collected to determine variations in the FA and antioxidant profiles of the biodiverse pasture, and different plant species were correlated with specific weather data and bioactive compounds (chapter 2). Beef samples were profiled for FAs and micronutrients (chapter 3). In the second study (n = 117), three groups of steers were kept on pasture and supplemented with either hay, baleage, or soybean hulls (SH). A fourth group was fed baleage and SH in feedlot. Beef FAs, micronutrients, and lipid peroxidation values were analyzed (chapter 4). Chapter 5 involved 54 RA steers fed either a grass diet, a total mixed ration, or a total mixed ration supplemented with grapeseed extracts (GSE). Beef FAs, micronutrients, and phytochemicals were analyzed. FAs were analyzed by gas chromatography-mass spectrometry (GC-MS), and phytochemicals were analyzed by ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). In chapter 2, the diverse pasture yielded higher levels of beneficial compounds (phenols, chlorophyll, carotenoids, n-3 PUFAs) compared to the total mixed ration, and early and late grazing season displayed the most beneficial nutritional profiles. In chapter 3, GFB exhibited higher levels of n-3 PUFAs, CLA, iron, and vitamin E compared to grain-finished beef, indicating a strong diet effect. Breed effects were only observed for a few specific FAs and micronutrients, and the interaction between diet and breed was not significant. In chapter 4, SH increased the n-6:n-3 ratio of beef, while supplementing GFB with hay resulted in the most favorable nutritional profile, with higher levels of long-chain n-3 PUFAs and a lower n-6:n-3 ratio compared to the other groups. However, the ratio remained under 2:1 for all treatments tested. In chapter 5, GFB exhibited a richer phytochemical profile compared to grain-finished beef and beef supplemented with GSE. Specific phytochemicals were also identified to discriminate between finishing diets. Altogether, GFB offers potential health benefits due to its beneficial FA profile and increased levels of phytochemicals compared to grain-finished beef. It was established that the diet had the strongest potential to modify the nutritional profile of beef. The supplemental feeds tested in this dissertation could not explain the large nutritional variations observed previously. Not all beef is equal in nutrient density, and distinctions should be made when considering the nutrient profile of beef. Future research should focus on the standardization of labeling practices for GFB and the effects of beef consumption from varying productions systems on human health.
Read
