Soybean Meal Can Be Replaced by Faba Beans, Pumpkin Seed Cake, Spirulina or Be Completely Omitted in a Forage-Based Diet for Fattening Bulls to Achieve Comparable Performance, Carcass and Meat Quality

SIMPLE SUMMARY: The sustainability of intensive beef production systems can be greatly improved using domestic protein sources as alternatives to imported soybean meal. Potential alternatives include indigenous grain legumes such as faba beans, food industry by-products including locally available oil cakes, or novel protein sources such as microalgae. Moreover, diets based on grassland-derived feeds increase dietary protein supply and have the potential to enhance food system sustainability. This study aimed to assess the effects on fattening performance, carcass and meat quality, and the meat fatty acid profile of beef cattle when replacing, or omitting, soybean meal in the diet. Bulls fed a grass/maize-silage based diet supplemented with concentrate containing either soybean meal, faba beans, pumpkin seed cake, or spirulina had similar growth performances and carcass and meat quality. No differences were observed in the meat fatty acid profiles. Most notably, omitting soybean meal without additional protein-concentrate replacements resulted in comparable carcass and meat quality without affecting the meat fatty acid profile while maintaining a high-performance level. Consequently, the grass silage-based diet supplemented with a grain-based concentrate without additional protein source was the most sustainable diet for growing bulls tested in this study. ABSTRACT: The aim of the study was to investigate the complete substitution of imported soybean meal in beef cattle diets and the consequences on performance, meat, and adipose tissue quality. Thirty growing crossbred Limousin bulls, with an initial bodyweight of 164 ± 13 kg and 4.3 ± 0.3 months of age, were fed a grass/maize-silage based diet with little additional concentrate (0.5:0.3:0.2). Concentrates contained either soybean meal (positive control), faba beans, pumpkin seed cake, or spirulina (Arthrospira platensis), resulting in about 226 g crude protein (CP)/kg concentrate dry matter (DM) and 158 g CP/kg total diet DM. A grain-based concentrate providing just 135 g CP/kg concentrate DM and 139 g CP/total diet DM served as a negative control. Bulls of all groups had comparable average daily gains (1.43 ± 0.1 kg) and feed intakes (6.92 ± 0.37 kg). Carcass and meat quality did not differ among groups. The fatty acid profile of meat lipids was hardly affected. These results indicate that soybean meal can be replaced by any of the tested protein sources without impairing performance or meat quality. Importantly, bulls fed the negative control achieved a fattening and slaughter performance comparable to that of the protein-supplemented groups without affecting meat and adipose tissue quality. Thus, the present findings suggest that feeding crossbred bulls a grass/maize-silage based diet does not require additional protein supplementation.