Influence of feeding multi-species pasture-based diets to cattle on the nutritional composition and quality characteristics of beef

Beef from pasture-based production systems is preferred by health conscious consumers, due to the improved nutritional profile of the meat when compared to beef from grain-fed ruminants. However, as consumers become increasingly aware of the environmental impact associated with animal-production systems, purchasing decisions have shifted towards a demand for nutritious, high-quality meat produced using more sustainable farming practices. Grazing ruminants on botanically-diverse pasture (BDP) could help improve the overall sustainability of the feeding system, while also maintaining the nutritional composition and quality associated with pasture-fed beef. Therefore, the aim of this research was to investigate the influence of feeding BDP based diets: (i) a perennial ryegrass (PRG) pasture, (ii) a perennial ryegrass + white clover (PRG+WC) pasture, (iii) a multi-species (MS) pasture, followed by a finishing period on silage with supplementary concentrates, on the nutritional composition and quality of beef from steers. Firstly, it was important to establish whether the fatty acid (FA) and antioxidant contents of the pastures grazed by the steers differed, as these differences could be reflected in muscle tissue of steers. Therefore, a study was undertaken to investigate the seasonal variation in the FA, tocopherol and carotenoid content of BDPs over a grazing season. Season had a greater influence than pasture-type on FA, tocopherol and carotenoid concentrations. Late-season pastures had higher concentrations of FAs, tocopherols and carotenoids compared to early and mid-season pastures. Higher concentrations of α-linolenic acid (C18:3n-3c) were observed in PRG pasture, whereas MS pasture had higher concentrations of C18:2n-6c, γ-tocopherol and lutein. A study was conducted to investigate the effect of feeding steers BDP based diets on the FA profile, tocopherol content and oxidative stability of beef. Feeding steers a MS pasture-based diet led to increased proportions of polyunsaturated fatty acids (PUFAs), higher polyunsaturated fatty acid:saturated fatty acid (PUFA:SFA) and n-6:n-3 ratios, and a lower α-tocopherol content in beef compared to feeding a PRG pasture-based diet. In addition, beef from steers on PRG+WC or MS pasture-based diets was more susceptible to oxidation once cooked, compared to beef from steers on PRG pasture-based diets. Headspace-trap gas chromatography-mass spectrometry (HS-trap GC-MS) was used to investigate the effect of feeding steers BDP based diets on volatile compounds and their relationship with FAs in beef. A HS-trap extraction technique did not identify as many volatiles (31 compounds) as a thermal desorption extraction technique (77 compounds). Muscle from steers on the MS pasture-based diet had higher abundances of lipid oxidation-derived volatiles, which were positively correlated with C18:2n-6c and C18:3n-3c muscle concentrations and negatively correlated with C18:1n-9c concentrations. A clear relationship was observed between high PUFA concentrations and greater abundance of lipid oxidation-derived compounds in muscle. The impact of feeding steers BDP based diets on the sensory quality of beef was investigated. No significant effect of diet was observed on the proximate composition, tenderness or sensory characteristics of the beef.